Dean  Frank  H.    Probert 


THE 


GENESIS  OF  ORE-DEPOSITS 


BY 


PROFESSOR  FRANZ  POSEPNY, 


REPRINTED,    TOGETHER    WITH    THE    DISCUSSION    THEREOF,   FROM 

VOLUMES   XXIII.  AND  XXIV.  OF  THE  TRANSACTIONS  OF 

THE  AMERICAN  INSTITUTE  OF  MINING  ENGINEERS. 


SECOND     EDITION. 


CONTAINING  ALSO  A  BIOGRAPHICAL  NOTICE  OF  PROFESSOR  POSEPNY,  AND  NlJ- 
MEROUS  ADDITIONAL  PAPERS  AND  DISCUSSIONS  BY  AMERICAN  AND  EURO- 
PEAN AUTHORS,  KEPRINTED  FROM  VOLUMES  xxx.  AND  xxxi. 
OF  THE  SAME  TRANSACTIONS. 


NEW  YOKK  CITY : 

PUBLISHED  BY   THE   INSTITUTE 

AT  THE  OFFICE  OF  THE  SECRETARY. 
1902. 


GIFT  OP 

FaANK  H  PROBERT 


DEFT. 


>vv 

DE?I. 


GENERAL  TABLE  OF  CONTENTS. 


PAGE 

Preface  to  the  Second  Edition, v 

Preface  to  the  First  Edition,          .........  vii 

Biographical  Notice  of  Franz  Posepny.     By  K.  W.  RAYMOND,    .         .         .  ix 

The  Genesis  of  Ore-Deposits.     By  PROFESSOR  FRANZ  POSEPNY,  ...  1 
Discussion  at  the  Chicago  Meeting,  August,  1893,  including  Communications 
Subsequently  Keceived  : 

W.  P.  BLAKE, 188 

ARTHUR  WINSLOW, ' 188 

T.  A.  RICKARD, 190 

HORACE  V.  WINCHELL, 192 

JOHN  A.  CHURCH, 195 

S.  F.  EMMONS, 199 

G.  F.  BECKER, 204 

F.  M.  F.  CAZIN, 206 

Discussion  at  the  Virginia  Beach  Meeting,  February,  1894,  including  Com- 
munications Subsequently  Received  : 

T.  A.  RICKARD, 211 

R.  W.  RAYMOND, .        .        .        .226 

H.  V.  WINCHELL,          . 227 

SECRETARY'S  NOTE, 232 

PROF.  POSEPNY, 232 

K.  W.  RAYMOND, 252 

F.  M.  F.  CAZIN, 269 

JOSEPH  LE  CONTE, 270 

Some  Principles  Controlling  the  Deposition  of  Ores.     By  C.  R.  VAN  HISE,  282 

The  Secondary  Enrichment  of  Ore-Deposits.     By  S.  F.  EMMONS,        .         .  433 

The  Enrichment  of  Gold  and  Silver  Veins.     By  WALTER  HARVEY  WEED,  473 

Metasomatic  Processes  in  Fissure- Veins.     By  WALDEMAR  LINDGREN,          .  498 
Discussion  : 

R.  BECK  (Papers  of  Van  Hise,  Emmons,  Weed  and  Lindgren),         .         .  613 

L.  DE  LAUNAY  ( Papers  of  Emmons  and  Weed), 616 

ARTHUR  L.  COLLINS  (Papers  of  Emmons  and  Weed),       ....  616 

H.  FOSTER  BAIN  (Papers  of  Van  Hise,  Emmons  and  Weed),    .         .         .  622 

CHARLES  R.  KEYES  ( Papers  of  Van  Hise  and  Lindgren),         .         .         .  628 

FRANK  D.  ADAMS  (Paper  of  Lindgren), 634 

Problems  in  the  Geology  of  Ore-Deposits.     By  Prof.  J.  H.  L.  VOGT,  .         .  636 

The  Role  of  the  Igneous  Rocks  in  the  Formation  of  Veins.     By  J.  F.  KEMP,  681 
The  Caliche  of  Southern  Arizona  :  An  Example  of  Deposition  by  Vadose 

Circulation.     By  WILLIAM  P.  BLAKE, 710 

M127002  (m) 


IV  GENERAL    TABLE    OF    CONTENTS. 

PAGE 

The  Character  and  Genesis  of  Certain  Contact-Deposits.     By  WALDEMAK 
LIXDGKEN, 716 

The  Formation  of  Bonanzas  in  the  Upper  Portions  of  Gold-Veins.     By  T. 
A.  KICKAKD 734 

Discussion  : 

S.  F.  EMMONS  (Papers  of  Collins,  Vogt,  De Launay,  etc.),        .         .        .756 

Some  Principles  Controlling  the  Deposition  of  Ores  (Concluding  Contribu- 
tion).    By  C.  K.  VAN  HISE,      .        ,        .        .        .        .        .         .         .763 

Appendix,     ............         .     782 


PREFACE  TO  THE  SECOND  EDITION. 


THE  first  edition  of  this  volume,  issued  in  1895,  and  con- 
taining only  the  famous  treatise  of  Posepny  and  the  discus- 
sions directly  based  upon  it,  was  exhausted  by  an  unexpectedly 
large  demand  from  students,  teachers  and  mining  engineers  in 
practice.  The  Council  of  the  Institute  authorized  the  publi- 
cation of  a  new  edition,  which  was  at  first  designed  to  be  a 
simple  reproduction  of  the  former  one,  with  the  addition  of 
the  Biographical  Notice  of  the  distinguished  author.  But  the 
presentation  of  certain  notable  papers  on  this  subject  at  the 
Washington  meeting  in  February,  1900,  led  to  the  decision 
that  these  papers,  with  the  discussions  thereof,  should  be  in- 
cluded in  the  new  edition. 

In  the  execution  of  this  plan,  it  was  found  impossible  to  in- 
clude papers  of  recognized  importance,  published  prior  to  1900, 
or  papers  on  cognate  subjects,  such  as  classifications  of  ore-de- 
posits, descriptions  of  special  deposits,  etc.,  published  since. 
The  Secretary's  Note,  constituting  the  Appendix  to  this  volume, 
gives  ample  proof  that  the  valuable  material  of  these  classes  con- 
tained in  the  Transactions  of  the  Institute  far  exceeds  the  capacity 
of  a  single  book.  Indeed,  the  publication  of  the  present  collec- 
tion is  not  intended  to  render  unnecessary  the  consultation  of 
many  papers  not  contained  in  it,  by  any  one  who  would  gain  a 
comprehensive  notion  of  the  science  to  which  it  relates.  Among 
such  papers,  it  would  be  easy  to  point  out  not  a  few,  equal  in 
value  to  those  which  are  here  reproduced.  With  regard  to  all 
these,  the  Secretary  can  only  express  his  regret  that  they  could 
not  be  included,  and  his  pride,  nevertheless,  that  the  material 
thus  necessarily  omitted  is  so  abundant  and  so  important. 

R.  W.  KAYMOND. 

DECEMBER,  1901. 


(v) 


PREFACE  TO  THE  FIRST  EDITION. 


THE  name  of  Franz  Posepny  appears  in  the  first  volume  of 
the  Transactions  of  the  Institute  as  one  of  its  foreign  members. 
At  the  Boston  Meeting  of  February,  1888,  he  was  elected  an 
honorary  member,  in  recognition  of  his  numerous  and  valuable 
contributions  to  the  literature  of  economic  geology,  and  par- 
ticularly to  the  science  of  ore-deposits,  which  has  borne  in 
Germany,  at  least,  since  the  days  of  the  brilliant  Gotta,  the  name 
of  Erzlagerstdttenlehre.  The  views  of  Cotta  and  his  associates, 
sometimes  called,  for  convenience,  "  the  Freiberg  school/'  dom- 
inated for  a  generation  the  current  theories  and  classifications 
of  mining  engineers.  This  is  particularly  true  of  the  United 
States,  where  the  excellent  translation  of  Cotta's  text-book  by 
Prof.  Frederick  Prime,  one  of  his  pupils,  and  one  of  the  orig- 
inal members  of  the  Institute,  was  for  many  years  the  control- 
ling, and,  indeed,  the  only  easily  available  authority  on  this 
subject  in  the  English  language. 

As  a  personal  friend,  diligent  student  and  hearty  admirer  of 
Bernhard  Cotta,  and  no  less  as  professional  critic  of  his  views, 
I  feel  myself  bound  to  say  that  his  theories,  as  stated  more  than 
thirty  years  ago,  are  still,  to  a  surprising  degree,  valid  and  com- 
prehensive. There  is  scarcely  a  single  modern  modification  of 
them  for  which  he  did  not,with  intuitive  prescience,  leave  a  place. 
On  the  other  hand,  it  is  a  fair  criticism  of  the  whole  "  Freiberg 
school,"  that  it  gave  too  much  prominence  and  attributed  too 
much  typical  importance  to  fissure-veins  of  the  class  represented 
in  the  Erzyebirge.  Such  writers  as  Groddeck  and  Grimm  have 
undoubtedly  aided  to  modify  this  disproportionate  emphasis. 
But  it  has  not  ceased  to  influence  the  conceptions  entertained 
by  miners,  and  even  by  legislators,  as  the  United  States  mining 
law  (evidently  based  on  the  "  true  fissure-vein  "  as  a  general 
type)  abundantly  demonstrates. 

Posepny  had  contributed  to  the  subject  numerous  mono- 
graphs, throwing  much-needed  light  upon  it  from  the  detailed 
study  of  special  mining  districts.  He  had  been  for  many  years 
devoted  to  this  particular  branch  of  geology,  and  had  occupied 

(vii) 


X          BIOGRAPHICAL  NOTICE  OF  FRANZ  POSEPNY. 

sonal  regret  for  his  accident  was  considerably  mitigated  by  the 
indirect  gain  thus  occasioned  to  his  translator. 

I  trust  that  I  do  not  transgress  propriety  by  saying  in  this 
place  a  few  words  concerning  Madame  Clotilde  Posepna,  who 
accompanied  her  distinguished  husband  in  his  visit  to  the 
United  States  in  1876  (as  on  so  many  of  his  other  journeys  and 
expeditions),  and  with  whom  so  many  members  of  the  Institute 
had  the  pleasure  of  becoming  acquainted  at  that  time.  With 
the  exception,  perhaps,  of  Sir  Charles  and  Lady  Lyell,  I  can 
recall  to  mind  no  other  husband  and  wife  so  highly  accom- 
plished, so  thoroughly  united  and  so  mutually  complementary 
in  scientific  work.  In  the  matter  of  languages,  for  instance,  I 
remember  hearing  one  of  them  say  that,  drawing  a  meridian 
through  eastern  Europe,  they  had  divided  the  map  between 
them ;  he  assuming  for  his  province  the  tongues  east  of  that 
line,  while  she  took  care  of  those  to  the  west,  including  all  the 
European  languages  and  literatures  that  we  commonly  regard 
as  required  for  linguistic  accomplishment.  German,  of  course, 
was  common  ground  to  both.  The  inestimable  value  of  such 
a  colleague  to  Prof.  Posepny  is  indicated  abundantly  in  his 
treatise,  already  mentioned,  which  exhibits,  on  the  one  hand, 
the  results  of  much  original  investigation  in  Eastern  Europe, 
and,  on  the  other  hand,  a  wide  acquaintance  with  the  tech- 
nical literature  of  western  nations.  That  treatise  aroused  so 
much  interest  among  mining  engineers  in  this  country,  and 
gave  rise  to  so  much  suggestive  discussion,  that  a  separate  vol- 
ume, containing  the  original  paper,  the  criticisms  which  it 
elicited,  and  Prof.  Posepny's  reply  thereto,  carefully  indexed 
for  convenient  consultation,  has  been  issued  by  the  Institute, 
to  accommodate  instructors  and  students.  It  was  just  as  this 
edition  was  leaving  the  press  that  I  received  the  news  of  Prof. 
Posepny's  death ;  and  in  view  of  the  part  which  his  wife  had 
taken  in  his  service  to  the  Institute  and  to  science,  I  inserted 
at  the  beginning  of  the  book  these  words,*  which  I  here  repeat, 
not  doubting  that  they  will  be  heartily  adopted  by  every  one 
who  shall  read  them  : 


*  This  dedication,  and  the  frontispiece-portrait  of  Posepny,  have  been  omitted 
from  the  present  volume. 


BIOGRAPHICAL  NOTICE  OF  FRANZ  POSEPNY.          XI 
TO 

MADAME  CLOTILDE 

WIFE,    COMRADE    AND    COLLEAGUE 
OF    THE    DISTINGUISHED    AND    LAMENTED 

AUTHOR    OF    THIS    TREATISE, 

THE    PRESENT    VOLUME    IS    INSCRIBED 

IN    WITNESS    OF    GRATITUDE    FOR    HER    CO-OPERATION, 

AND    SYMPATHY    WITH    HER    BEREAVEMENT. 

In  attempting  to  sketch  the  career  of  Franz  Posepny,  I  shall 
make  free  use  of  the  appreciative  obituary  notice  written  by 
his  friend  and  colleague,  Oberbergrath  Eitter  C.  von  Ernst,  one 
of  the  editors  of  the  Oest.  Zeitsch.  fiir  Berg-  und  Hiittenwesen,  and 
published  in  that  journal  April  27,  1895. 

Born  March  30, 1836,  at  Starkenbach,  in  Bohemia,  Posepny, 
after  preliminary  courses  in  various  Bohemian  schools,  entered, 
in  1852,  the  Polytechnic  School  at  Prague,  with  the  special  pur- 
pose of  pursuing  the  natural  sciences,  for  which  he  had  a  native 
inclination.  In  addition  to  the  prescribed  curriculum,  he  zeal- 
ously frequented  the  lectures  and  practical  exercises  in  botany, 
mineralogy,  geology,  palaeontology,  chemistry,  technology,  met- 
allurgy, etc.  In  order  to  utilize  in  the  department  of  mining 
his  knowledge  of  geology,  he  went,  in  1857,  to  the  mining 
school  at  Przibram,  where  he  was  specially  interested  in  the 
lectures  of  Director  Grimm  on  the  science  of  ore-deposits.  It 
was  from  Grimm  (says  his  German  biographer,  on  the  author- 
ity of  Posepny's  own  notes)  that  he  heard  for  the  first  time  the 
view  that  ore-deposits  are  characteristically  confined  to  decom- 
posed rocks — a  doctrine  which  guided  and  influenced  him  for 
many  years  after.  After  finishing  his  mining  course,  he  en- 
tered (1859)  the  State  service,  and  was  first  assigned,  without 
pay,  to  the  government  bureau  at  Nagybanya,  and  thence 
(1860),  at  a  salary  of  less  than  50  cents  a  day,  to  Ohlalapos- 
banya,  in  Transylvania.  This  region,  with  its  complicated 
mine-workings  and  vein-phenomena,  was  peculiarly  interesting 
and  stimulating  to  an  ardent  young  mining  engineer  and  in- 
vestigator ;  but  he  was  condemned  to  the  prosaic  drudgery  of 
auditing  the  old  accounts  of  mines  which  had  been  destroyed 


Xll  BIOGRAPHICAL    NOTICE    OF    FRANZ    POSEPNY. 

in  the  rebellion  of  1848,  and  his  superior  official  discouraged 
his  studies  underground,  telling  him  that  he  had  "  much  more 
important  things  to  attend  to  than  going  down  into  old  mines, 
which    could   show   him    only   rubbish   and   dirt."     He   was 
obliged,  therefore,  to  pursue  his  favorite  studies  in  secret  until 
a  more  favorable  position  was  assigned  to  him  as  the  director 
(at  about  60  cents  per  day !)  of  certain  explorations  for  lignite 
in  the  district  of  Kovar.     Here  he  distinguished  himself  by  the 
execution  of  a  topographical  and  geological  map  of  the  district, 
determining,  on  palaeontological  evidence,  the  age  of  the  coal- 
deposits.     This  led  to  a  recognition  of  his  peculiar  qualifica- 
tions for  the  study  of  problems  in  economic  geology;   and  in 
1862  he  was  designated  (at  the  increased  salary  of  75  cents  per 
day !)  to  make  an  investigation  of  the  ore-deposits  and  almost 
abandoned  mines  of  Rodna,  in  Transylvania.     This  work,  in 
which  he  at  first  received  assistance  from  the  Geologische  Reichs- 
anstalt  at  Vienna,  was  subsequently  somewhat  peremptorily 
and  prematurely  terminated,  and,  late  in   1865,  Posepny  was 
ordered  to  make  a  similar  study  of  the  gold-mines  of  Veres- 
patak.     This  occupied  him  until  1869,  when  he  was  recalled  to 
Vienna,  and  directed  to  examine  and  report  upon  the  mines  of 
Raibl,  in  Carinthia.     This  work  consumed  a  good  deal  of  time, 
and  the  authorities  were,  perhaps,  inconsiderate  in  their  re- 
peated demands  for  a  hasty  completion  of  it.     Posepny  was 
still,  after  11  years  of  service,  only  an  "expectant,"  without 
title  and  with  scanty  pay;  and  in  justifiable  dissatisfaction  with 
this  treatment,  he  accepted,  in  1870,  the  offer  of  an  independ- 
ent position — specially  created  for  him — as  economic  geologist 
for  Hungary,  with  a  salary  and  allowances  amounting  to  some- 
thing like  $1000  per  annum.     This  he  occupied  for  two  years, 
executing  during  that  period  many  investigations  of  value  to 
the    Hungarian    mining   industry.     In    1872    he    returned    to 
Raibl;   finished   and  presented,  in  1873,  his  official  report  on 
that  district,  and  then  went  back  to  Hungary,  to  continue  his 
study  of  the  Schemnitz  region.     But  by  this  time  his  services 
were  required  in  a  wider  field ;  and  he  resigned  his  position  in 
Hungary  to  accept  that  of  Vice-Secretary  in  the  Royal-Imperial 
Ministry   of  Agriculture   (including  mining)   of  Austria.     In 
this  capacity,  from  1873  to  1879,  he  carried  out  in  Tyrol  and 
Salzburg  a  series  of  investigations  (published  in  the  first  vol- 


BIOGRAPHICAL    NOTICE    OF    FRANZ    POSEPNY.  Xlll 

ume  of  his  Archiv  fiir  Praktische  Geologic),  and  also  made 
journeys  to  various  countries,  including  an  extended  tour  in 
the  United  States. 

But  he  was  not  satisfied  with  this  achievement  of  official 
position  and  its  sphere  of  usefulness.  His  conviction  of  the 
importance  to  the  mining  industry  of  the  scientific  study  of 
mineral  deposits  had  been  expressed  incessantly  in  publica- 
tions, urging  the  introduction  of  special  lectures  on  this  subject 
in  mining  schools  ;  and  in  1879,  the  ministry  with  which  he 
was  connected  succeeding  in  obtaining  from  the  Emperor 
authority  to  establish,  at  the  academies  of  Leoben  and  Przi- 
bram,  separate  chairs  devoted  to  that  department,  the  pro- 
fessorship at  Przibram,  together  with  the  title  of  Bergrath,  was 
given  to  Posepny,  and  occupied  by  him  until,  in  1888,  he  re- 
tired from  public  service,  receiving  in  recognition  of  his  merit 
the  order  of  the  Iron  Crown. 

In  some  respects,  his  labors  at  Przibram  were  the  most  fruit- 
ful of  his  life.  Besides  discharging  the  duties  of  the  class- 
room, which  served,  no  doubt,  to  consolidate  and  systematize 
the  knowledge  gathered  in  practice,  he  added  to  that  knowl- 
edge by  a  diligent  and  minute  study  of  the  geology  and  vein- 
relations  of  the  extensive  and  productive  Przibram  mines. 
This  really  great  investigation  was  carried  through  by  Pro- 
fessor Posepny  with  wonderful  persistency,  at  great  personal 
expense,  and  without  assistance.  Its  results  are  to  be  pub- 
lished in  the  second  volume  of  his  Archiv  fiir  Praktische  G-eolo- 
gie,  which  was  in  press  at  the  time  of  his  death. 

After  resigning  his  professorship  and  retiring  from  active 
service,  he  established  himself,  with  his  inseparable  helpmate, 
in  a  pleasant  cottage  home  in  the  suburbs  of  Vienna,  where  he 
devoted  himself  more  exclusively  than  ever  to  his  favorite 
studies,  making  journeys  of  observation  to  Transylvania,  Ger- 
many, Switzerland,  the  Ural,  France,  England,  Sweden,  Nor- 
way, Italy,  Sardinia,  and  finally,  in  the  spring  of  1894,  to 
Greece  and  the  Orient,  as  far  as  Jerusalem.  His  principal 
attention  in  these  journeys  was  given  to  the  geology  and  the 
mining  (present,  historical  or  pre-historical)  of  the  countries  he 
visited.  That  he  could  appreciate,  however,  other  sentiments 
and  associations,  I  have  touching  proof  in  a  note  which  he 
sent  me  from  Jerusalem,  enclosing  a  leaf  plucked  on  the  Mount 


XIV  BIOGRAPHICAL    NOTICE    OF    FRANZ    POSEPNY. 

of  Olives.  It  should  be  mentioned  also  that,  in  addition  to  his 
main  specialty,  he  was  an  enthusiastic  student,  and  no  mean 
authority,  in  anthropology  and  numismatics. 

During  this  closing  period  of  his  intensely  active  life,  his  in- 
dustry might  fairly  be  called  desperate ;  for  the  increase  of  a 
long-standing  pulmonary  weakness,  to  which  in  these  latter 
years  a  disease  of  the  heart  was  added,  produced  in  him  the 
abiding  conviction,  not  only  that  his  days  were  numbered,  but 
that  they  might  at  any  moment  suddenly  end.  What  he  ac- 
complished with  failing  strength  and  under  such  a  depressing 
consciousness,  is  truly  amazing.  Yet,  in  his  letters  to  me,  he 
never  alluded  to  the  shadow  of  such  an  apprehension ;  and  I 
did  not  dream  that  his  magnificent  contribution  to  the  Insti- 
tute was  the  bequest  of  a  dying  man,  and  the  last  important 
work  of  his  life.  I  take  the  liberty  of  translating  portions  of  a 
private  letter  from  his  wife,  which,  although  not  intended  for 
publication,  are  calculated  to  give,  better  than  words  of  mine 
could  do,  a  pathetic  and  inspiring  picture  of  his  heroic  devo- 
tion : 

"  Although  for  many  months  I  had  necessarily  foreseen  the  sad  termination  of 
his  sufferings,  I  could  not  help  clinging  to  occasional  momentary  gleams  of  hope  ; 
and  the  end  seemed,  after  all,  awfully  sudden. 

"Only  with  the  utmost  exertion  did  we  two  succeed  in  so  far  completing  the 
proof-reading  of  the  second  volume  of  the  Archiv,  that  nothing  will  now  prevent 
its  early  publication. 

"With  the  kind  assistance  promised  by  his  professional  colleagues,  I  may  also 
hope  to  bring  out,  in  a  year  or  two,  a  third  volume.  It  is  a  purpose  dear  to  me 
to  publish  all  that  he  left  behind.  Much  will,  of  course,  appear  in  fragmentary 
form,  but  it  will  at  least  stimulate  thought  and  discussion. 

"It  is  almost  incredible  how  hard  he  worked,  giving  himself  in  later  years  no 
rest,  because  he  continually  looked  for  death.  Outwardly  he  appeared  so  full  of 
life  and  pleasure  in  life  (so  lebensfroh),  and  seemed  to  be  in  perfect  health.  But  I 
knew  better  ;  and  he  himself  used  to  be  annoyed  when  people  spoke  of  his  good 
looks,  for,  as  he  said,  he  was  always  '  only  a  handsomely  turfed  grave  !'  }: 

I  am  unable  to  give  at  this  time  a  complete  list — still  less  a 
critical  account — of  the  published  reports  and  treatises  of  Prof. 
Posepny,  between  one  and  two  hundred  in  number.  This  will 
be  done,  I  understand,  in  the  introduction  to  the  second  vol- 
ume of  his  Archil^  now  in  press.  Nevertheless,  I  may  venture 
to  express  some  general  reflections  concerning  his  career  and 
his  position  in  scientific  literature. 

1.  Even  from  the  bare  outline  of  his  life  which  I  have  given, 


BIOGRAPHICAL    NOTICE    OF    FRANZ    POSEPNY.  XV 

it  is  evident  that  he  trod  no  easy  path  to  eminence  and  fame. 
For  many  years  he  was  utilized  without  being  adequately  ap- 
preciated ;  ordered  from  place  to  place ;  scantily  paid  and  arbi- 
trarily overruled;  his  far-reaching  plans  thwarted  by  short- 
sighted officialism,  intent  upon  more  immediate  practical  re- 
sults. For  this  the  government  bureaus  are  not  necessarily  to 
be  blamed.  Posepny  was,  heart  and  soul,  not  a  government 
official,  but  the  lover  and  slave  of  science.  And  governments 
do  not  exist  for  the  promotion  of  science.  The  utmost  which 
they  can  legitimately  do  in  that  direction  is  to  assist  the  prog- 
ress of  science  on  grounds  of  political  economy ;  that  is,  as  an 
element  in  the  industrial  prosperity  of  the  commonwealth,  and 
an  incident  of  the  intelligent  administration  of  its  resources. 
European  states  have  gone  further  in  theory  than  our  own 
Federal  government  (though  few  have  been  so  loosely  liberal 
in  practice)  in  the  range  of  application  given  to  this  principle. 
But,  under  any  government,  immediate  administrative  necessi- 
ties may  often  take  precedence  of  purely  scientific  investiga- 
tions, and  the  subordinates  of  a  bureau  may  be  commanded  to 
devote  themselves  to  barren  routine  when  they  would  rather  be 
"  exploring  the  unknown." 

2.  Moreover,  not  everybody  who  burns  with  ambition   to 
distinguish  himself  by  increasing  the  sum  of  permanently  valu- 
able human  knowledge  should,  on  that  account,  be  enabled, 
either  by  public  or  by  private  aid,  to  pursue  his  supposed  mis- 
sion at  the   expense  of  other  people.     Some   peculiar  fitness 
must  first  be  demonstrated ;  and,  on  the  whole,  there  is  per- 
haps no  better  test  than  that  of  patient  and  obedient  service, 
even  under  unwelcome  restraint.     The  man  who,  like  Posepny, 
in  spite  of,  and  in   addition  to,  his  routine  duties,  continues 
with  ardor  his  scientific  investigations,  is  the  best  man  to  be 
subsequently  intrusted  with  such  higher  work. 

3.  But  this  is  not  all.     The  best  training,  even  for  a  specialty, 
does  not  consist  in  simply  encouraging  the  inclination  of  genius 
in  one  direction.     We  hear  a  good  deal  about  education  as 
being   ideally,  as  it  is  etymologically,  the  "  drawing-out "  of 
what  is  already  in  the  pupil.     This  is  true  enough,  if  we  add 
that  the  best  work  of  education  is  the  drawing-out  of  faculties 

O 

which  the  pupil  does  not  know  or  believe  to  be  in  him,  and 
that  its  least  important  function  is  the  assistance  of  those  domi- 


XVI  BIOGRAPHICAL    NOTICE    OF    FRANZ    POSEPNY. 

nant  powers  and  purposes  which  need  little  help.  It  is  often 
in  the  branch  for  which  the  schoolboy  shows  no  taste  or  ca- 
pacity that  he  should  be  most  rigorously  drilled,  not  merely  for 
the  moral,  but  also  for  the  mental,  discipline  thus  secured. 
And  there  is  nothing  that  contributes  more  potently  to  success 
in  the  larger  school  of  life  than  the  subjection  of  young  men  to 
work  which  they  do  not  like,  and  in  the  knowledge  of  which 
they- are,  consequently,  deficient.  I  say  "consequently,"  but 
the  consequence  may  be  often  the  cause.  The  dormant  capacity 
once  developed  by  practice,  many  a  man  ends  by  liking  a  work 
which  he  understands,  who  began  by  disliking  it  because  he 
did  not  understand  it. 

4.  In  the  case  of  Posepny,  I  am  not  at  all  sure  that  the  dis- 
appointment and  drudgery  of  his  early  career  were  not  the 
best  things  that  could  have  happened  to  him.  Incidentally, 
they  gave  him  a  much  wider  experience  than  he  would  have 
obtained  by  rapid  promotion — which  might  have  made  of  him 
either  a  conservative  official,  calmly  contemptuous  of  youthful 
ambitions,  or  a  library-theorist,  learnedly  discoursing  of  nature 
at  second-hand;  of  both  of  which  classes  the  world  has  enough 
already.  They  are  useful  in  their  way;  but  it  would  have 
been  a  pity  to  waste  Posepny,  in  order  to  increase  either. 

The  result,  in  his  case,  of  the  irksome  discipline  of  fiery,  un- 
conquerable genius,  was  to  reinforce  the  knowledge  of  litera- 
ture and  theory  with  an  extensive  and  intimate  direct  knowl- 
edge of  nature,  and,  above  all,  to  make  the  chemist  and  geolo- 
gist also  a  practical  miner  and  mining  engineer.  The  latter 
circumstance  adds  exceptional  and  characteristic  weight  to  his 
scientific  generalizations.  I  may  add  that,  in  my  judgment, 
the  nature  of  his  early  labors  not  improbably  bred  or  deep- 
ened in  him  that  sense  of  the  vital  importance  to  science  of 
the  minute  observation,  and  purely  "objective"  description, 
of  single  groups  of  phenomena,  which  is  so  prominent  in  all 
his  writings.  In  accordance  with  it,  his  works  are  mainly  de- 
tailed accounts  and  discussions  of  single  mining  districts.  In 
other  words,  he  continued  to  the  end  the  method  of  investiga- 
tion which  was  forced  upon  him  in  the  beginning  by  superior 
authority.  The  difference  between  such  monographs,  pro- 
duced by  the  patient  labor  of  months  in  each  locality,  and  the 
sketchy  results  of  hasty  visits  by  expert  tourists,  such  as  con- 


BIOGRAPHICAL    NOTICE    OF    FRANZ    POSEPNY.  XV11 

stitute  much  of  the  literature  of  this  class,  requires  no  com- 
ment. 

5.  I  have   emphasized  at  some  length  this  feature  of  Po- 
sepny's  work,  because  I  think  it  carries  an  important  lesson  foi 
American  mining  engineers  and  geologists.     We  are  making 
rapid  progress  in  science ;  but  we  do  it  in  a  tumultuous  and 
irregular  fashion,   accumulating  a  goodly  stock   of    untrust- 
worthy data  and  of  premature  theories  as  we  go.     Our  young 
investigators   are  often  in  a  hurry  to  promulgate  generaliza- 
tions ;  and,  on  the  other  hand,  our  practicing  mining  engineers 
are  often  too  busy  to  observe  and  record  facts.     The  two  classes 
could  aid  each  other  more  than  they  do ;  and  especially  those 
who  are  confined  by  their  duties  to  one  locality  might  learn 
from  the  example  of  Posepny  that  the  thorough  study  of  one 
locality  is  the  most  valuable  contribution  that  can  be  made  to 
general  science.     On  the  other  hand,  the  authors  of  theories 
may  profitably  note  that   Posepny  himself,  as  the  result  'of 
wider  observation,  was  obliged  to  change  the  views  he  had  ex- 
pressed, under  the  influence  of  preconceived  impressions,  in 
early  years. 

6.  In  my  brief  preface   to   the    separate    edition    of  "The 
Genesis  of  Ore-Deposits,"  issued  by  the  Institute,  I  have  used 
the  following  language,  which  I  here  repeat,  as  an  introduction 
to  some  further  observations  upon  Posepny's  work : 

"  The  views  of  Cotta  and  his  associates,  sometimes  called  for 
convenience  <  the  Freiberg  school,'  dominated  for  a  generation 
the  current  theories  and  classifications  of  mining  engineers. 
This  is  particularly  true  of  the  United  States,  where  the  excel- 
lent translation  of  Cotta's  text-book  by  Prof.  Frederick  Prime, 
Jr.,  one  of  his  pupils,  was  for  many  years  the  controlling,  and 
indeed  the  only  easily  available,  authority  on  this  subject  in  the 
English  language. 

"  As  a  personal  friend,  diligent  student  and  hearty  admirer 
of  Bernhard  Cotta,  and  no  less  as  professional  critic  of  his 
views,  I  feel  myself  bound  to  say  that  his  theories,  as  stated 
more  than  thirty  years  ago,  are  still,  to  a  surprising  degree, 
valid  and  comprehensive.  There  is  scarcely  a  single  modern 
modification  of  them  for  which  he  did  not,  with  intuitive  pres- 
cience, leave  a  place.  On  the  other  hand,  it  is  a  fair  criticism 
of  the  whole  c  Freiberg  school,'  that  it  gave  too  much  promi- 


XV111  BIOGRAPHICAL    NOTICE    OF    FRANZ    POSEPNY. 

nence  and  attributed  too  much  typical  importance  to  fissure- 
veins  of  the  class  represented  in  the  Erzgebirge.  Such  writers 
as  Groddeck  and  Grimm  have  undoubtedly  aided  to  modify 
this  disproportionate  emphasis.  But  it  has  not  ceased  to  in- 
fluence the  conceptions  entertained  by  miners,  and  even  by 
legislators,  as  the  United  States  mining  law  (evidently  based 
on  the  true  c  fissure-vein  '  as  a  general  type)  abundantly  demon- 
strates." 

Of  the  two  authorities  named  in  the  above  extract,  as  aiding 
to  modify  the  views  of  the  "  Freiberg  school,"  Bergrath  Dr. 
Albrecht  von  Groddeck,  whose  treatise  appeared  in  1879,  was 
the  director  of  the  Prussian  Mining  Academy  at  Clausthal. 
His  treatment  of  the  science  of  ore-deposits  was  chiefly  char- 
acterized by  the  recognition  of  numerous  "  types,"  and  the 
citation  of  leading  examples  under  each  type.  Oberbergrath 
Johann  Grimm,  whose  treatise  appeared  in  1869,  was  director 
of  the  Austrian  Mining  Academy  at  Przibram,  in  Bohemia; 
and  it  was  in  Grimm's  lecture-room,  from  1857  to  1859,  that 
Posepny  received  his  first  working-theory  of  the  nature  and 
origin  of  mineral  deposits.  I  must  confess  that  I  cannot  find 
in  Grimm's  book,  published  ten  years  later,  the  sweeping  gen- 
eralization to  which,  on  Posepny's  authority,  Bitter  von  Ernst 
(as  quoted  by  me  above)  alludes ;  and  I  am  led  to  suppose  that 
the  veteran  instructor  had  seen  cause,  before  1869,  to  modify 
his  views.  However  that  may  be,  it  was  as  a  disciple  of  Grimm 
that  Posepny  began  his  work ;  and  it  was  only  after  years  of 
patient  study  of  facts  in  the  field,  that  he  promulgated  any 
comprehensive  system  of  his  own. 

.  7.  That  system,  his  matured  statement  of  which  is  found  in 
"  The  Genesis  of  Ore-Deposits,"  cannot  be  said  to  involve  any 
appeal  to  newly-discovered  causes,  or  any  denial  of  accepted 
principles  in  geology.  The  same  is  true  of  all  systems  pro- 
posed since  the  exclusive  agency  of  plutonic  action  on  the 
one  hand,  or  of  aqueous  action  on  the  other,  was  recognized  as 
untenable.  They  have  all  been  simple  attempts  to  classify  the 
observed  facts  for  fruitful  study,  and  to  estimate  the  relative 
importance  of  the  several  natural  agencies  which  were  univer- 
sally recognized  as  factors.  For  the  purpose  of  classification, 
the  chief  distinctive  characters  have  always  been  :  (1)  The  time- 
relations  of  a  mineral  deposit,  as  foraged  simultaneously  with 


BIOGRAPHICAL    NOTICE    OF    FRANZ    POSEPNY.  XIX 

the  enclosing  rock,  or  as  a  regular  member  of  a  series  of  rocks, 
or  as  a  later  segregation  or  intrusion ;  (2)  its  form ;  (3)  the 
manner  and  agencies  of  its  origin ;  and  (4)  its  contents.  Of 
these  characters,  sometimes  one  and  sometimes  another  has 
been  treated  as  the  primary  distinction.  Gold-,  silver-,  lead-, 
and  copper-mines,  etc.,  may  have  been  the  leading  classes  in  a 
system  designed  for  convenient  use  in  practice ;  veins,  stock- 
works  and  impregnations  may  have  been  separated  as  groups 
of  independent  significance  in  another  practical  system ;  orig- 
inal deposits  may  have  been  combined  with  deposits  of  subse- 
quent formation,  if  both  were  supposed  to  have  originated 
through  the  same  processes,  etc.  For  the  purposes  of  science, 
it  will  probably  be  admitted  that  a  genetic  classification  is  to 
be  preferred;  and  such  a  classification  Posepny  proposed.  That 
it  was  not  final  or  complete  he  acknowledged,  not  only  ex- 
pressly in  words,  but  tacitly  by  his  preliminary  division  of 
minerals  as  "  idiogenous  "  and  "  xenogeiious,"  and  the  practical 
confinement  of  his  genetic  classification  to  the  latter.  It  is,  of 
course,  plain  that  the  idiogenous  minerals  must  likewise  have 
had  a  genesis,  and  that  a  complete  genetic  classification  would 
include  them,  not  as  a  separate  primary  group,  but  as  parts  of 
other  groups,  determined  by  the  conditions  and  agencies  of 
their  origin.  Posepny 's  system,  beginning  as  it  does  with  the 
rocks  already  formed,  and  ignoring  their  prior  genetic  history, 
is,  to  that  extent,  an  avowed  compromise.  But  it  is  on  that 
basis  to  be  judged,  and  not  by  comparison  with  something 
more  ambitious  and  comprehensive,  at  which  the  author  did 
not  pretend  to  aim.  My  views  on  this  subject  have  been  suffi- 
ciently set  forth  elsewhere ;  and  the  position  of  Posepny  has 
been  so  clearly  and  fully  stated  by  himself  as  to  render  further 
exposition  needless. 

8.  In  fact,  the  present  state  of  the  science  of  mineral  de- 
posits is  such  as  to  render  any  man's  system  of  classification  a 
matter  of  subordinate  pedagogic  importance.  The  declared 
purpose  of  Professor  Posepny,  in  the  presentation  to  the  Insti- 
tute of  what  he  at  first  entitled  "  Subjective  Views  of  the  Ori- 
gin of  Ore-Deposits,"*  was  to  invite  criticism  and  discussion. 
This  purpose  was  unquestionably  realized  in  a  discussion  (not 


*  See  my  remarks,  Trans,  xxiv.,  980,  and  in  the  present  volume,  p. 


XX  BIOGRAPHICAL    NOTICE    OF    FRANZ    POSEPNY. 

yet  ended)  of  great  interest  and  value.  And  the  remarkably 
stimulating  effect  of  that  treatise  seems  to  me  typical  of  the 
chief  permanent  effect  of  the  author's  whole  work,  in  the  field 
in  which  he  became  pre-eminent.  I  believe  it  will  be  the  ver- 
dict of  his  successors,  as  of  his  contemporaries  : 

a.  That  he  furnished  an  example  of  unselfish  and  unqualified 
devotion  to  science,  which  will  be  an  inspiration  forever. 

b.  That  he  contributed  to  science,  in  his  special  department, 
an  immense  amount  of  careful  and  accurate  fundamental  work, 
which  can  be  confidently  relied  upon  as  trustworthy  material 
for  future  study,  being  guaranteed,  riot  only  by  his  eminence 
in  general  science,  but  also  by  his  familiarity,  as  a  mining  en- 
gineer, with  operations  and  observations  underground. 

c.  That,  on  the  basis  of  his  wide  observation,  coupled  with 
his  extensive  knowledge  of  technical  literature,  he  exerted   a 
potent  influence  in  promoting  the  scientific   study  of  ore-de- 
posits and  in  correcting  extreme  theories  and  tendencies  which 
have  tended  to  bias  and  distort  that  science. 

9.  In  the  last  proposition,  I  have  in  mind  more  particularly 
the  controversy  which  Posepny  and  his  friend,  the  late  Prof. 
Stelzner,  of  Freiberg,  waged  against  the  lateral-secretion  the- 
ory of  Prof.  Sandberger.  In  this  debate  Posepny  no  doubt  as- 
sumed to  some  extent  the  attitude  of  a  partisan ;  and,  perhaps, 
in  some  respects,  his  controversial  utterances  may  have  gone 
beyond  a  judicial  impartiality.  This  has  been  pointed  out 
more  than  once  by  his  critics,  and  particularly  in  the  discussion 
of  his  recent  treatise  in  the  Transactions  of  the  Institute.  As 
I  have  elsewhere  declared,  I  think  he  was  right  in  his  general 
view  and  argument,  and  I  will  here  do  no  more  than  call  at- 
tention to  the  circumstance  that  those  of  his  statements  which 
have  been  seriously  contested  by  American  authorities  were 
mainly  based  upon  the  publications  of  others,  not  upon  his  own 
observation.  Many  such  publications  are  affected  with  "  sub- 
jective "  opinions;  many  of  them  are  unaccompanied  with  ac- 
curate drawings ;  and  many  of  them  lack  precision  in  descrip- 
tion, and  are,  therefore,  liable  to  misinterpretation.  It  is  no 
wonder  that  in  single  cases  Posepny  may  have  mistaken  the 
intended  meaning  of  an  author  or  accepted  too  hastily  an  as- 
sertion too  hastily  made.  But  it  must  be  confessed  that,  as  a 
whole,  his  survey  of  the  literature  of  his  subject  was  singularly 
comprehensive,  intelligent  and  fair. 


BIOGRAPHICAL  NOTICE  OF  FRANZ  POSEPNY.        XXI 

10.  As  I  have  observed  already,  Posepny's  final  work  was 
not  offered  as  the  last  word  of  science  in  that  field.  We  now 
know,  what  he  knew  when  he  wrote  it,  that  it  was  his  last 
word — the  utterance  of  one  who  was  about  to  turn  over  to 
others  the  results  of  a  life-labor  still  incomplete,  and  surpassing 
in  fruitful  suggestion  even  its  illustrious  record  of  accomplished 
achievement.  The  loss  of  such  a  man  at  any  time  is  deplora- 
ble; but  doubly  so  when  he  departs  in  the  prime  of  years,  just 
prepared  for  the  ripest  and  richest  harvest  of  all  his  planting. 
Posepny's  views  will  still  incite  and  reward  discussion ;  but  we 
shall  sorely  miss  the  ablest  of  expositors  and  critics  in  Posepny 
himself. 

It  has  been  my  endeavor  in  the  foregoing  sketch  to  preserve 
the  standpoint  of  disinterested  justice;  but  I  cannot  deny  that, 
while  I  have  been  thus  coldly  analyzing  and  estimating  the 
scientific  leader,  there  has  been  constantly  present  with  me  a 
vision  of  the  splendid  presence  of  my  own  dear  friend.  I 
never  saw  him  but  once — at  the  time  of  his  visit  to  this  country 
in  1876.  But  that  meeting  confirmed  the  personal  attraction 
already  exercised  upon  me  by  his  works ;  and  our  subsequent 
intercourse  by  correspondence  made  the  charm  perpetual  and 
indissoluble.  A  few  such  friends  I  may  still  count  in  foreign 
lands,  unseen,  yet  ever  present;  and  it  sometimes  seems  to  rne 
that  these  relations  of  mind  and  heart,  which  defy  separation 
in  space,  are  the  best  types  of  the  relation  which  defies  death 
also.  At  all  events,  I  find  that  he  and  I,  who  could  be  to- 
gether, though  confined  to  the  Old  and  the  New  World  respec- 
tively, are  not  less  mutually  near,  now  that  one  of  us  has  en- 
tered the  World  which  lies  so  close  to  both. 


THE  GENESIS  OF  ORE-DEPOSITS. 

BY  PROF.  FRANZ  POSEPNY,  VIENNA,  AUSTRIA. 


CONTENTS. 

INTRODUCTION. 
PART  I. — GENERAL  FACTS  AND  THEORIES. 

PAGE 

1.  Systems  of  Classification  Employed  Hitherto,  .  .3 

2.  Standpoint  and  View  of  the  Present  Paper,  .  .  .10 

3.  The  Xenogenites  in  General,         .         .         .  .  .12 

4.  The  Subterranean  Water- Circulation,    .         .  .  .17 

A.  The  Vadose  Underground  Circulation,          .         .     18 

Filling  of  Open  Spaces  Formed  hy  Vadose  Circulation,     .  .        23 

B.  The  Deep  Underground  Circulation,     .         .          .26 

Ascending  Waters  Encountered  in  Mines,  .            .            .  .28 

Related  Phenomena  near  the  Surface,          .            .            .  .32 
Mineral  Springs  at  the  Surface,         .....        38 

Chemical  Constitution  of  Mineral  Waters,  .            .           .  .40 

Minute  Metallic  Admixtures  in  Mineral  Waters,  .            .  .45 

Alterations  Produced  by  Mineral  Springs,  .            .            .  .48 

Structural  Features  of  the  Deposits  of  Mineral  Springs,  .  .        52 

5.  Origin  of  Ore-Deposits  in  the  Deep  Region,   .         .         .55 

Manner  of  Filling  of  Open  Spaces  in  General,       .  .  .64 

PART  II. — EXAMPLES  OF  CLASSES  OF  DEPOSITS,  72 

1.   Ore-Deposits  in  Spaces  of  Discission,    .         .         .         .74 
General  Features  and  Illustrations. 

a.  Ore-Veins  in  Stratified  Rocks,    .         .         .         .79 

Clausthal,  79  ;  Andreasberg,  81. 

b.  Ore-Veins  in  the  Neighborhood  of  Eruptive  Masses,  82 

The  Erzgebirge,  82  ;  Przibram,  83. 

c.  Ore-Veins  Wholly  Within  Large  Eruptive  For- 

mations, .......     85 

Hungary,  85  ;  Dacian  Gold-field,  86  ;  Verespatak,  87  ;  Vulkoj,  88 ; 
Comstock  lode,  89. 


Z  "     THE    GENESIS    OF    ORE-DEPOSITS. 

PAGE 

2.  Ore-Deposits  in  Soluble  Rocks,  .         .         .         .         .95 
Fillings  of  Spaces  of  Dissolution  and  Metasomatic  Deposits. 

Kodna,  95  ;  Offenbanya,  98  ;  Kezbanya,  98  ;  Eaibl,  102  ;  North  of  Eng- 
land, 104 ;  Leadville,  Colo.,  106  ;  Ked  Mountain,  Colo.,  109  ;  Utah, 
110  ;  Nevada,  110  ;  Deposits  in  Structural  Plateaux,  115  ;  Valle  aii.l 
Mine  la  Motte,  Mo.,  115,  117;  Wisconsin,  117. 

3.  Metamorphous  Deposits,    .         .         .         .         .         .118 

General  Features. 

a.  Ores  in  Distinctly  Stratified  Rocks, .         .         .120 

Deposition  of  Ores  from  Sea- Water,  121  ;  from  Fresh  Water,  123; 
the  Copper-Schists  of'Mannsfeld,  123  ;  of  Bohemia,  124  ;  of  Thii- 
ringia,  124;  of  Westphalia,  J25;  the  Copper-Sandstone  of  Bohe- 
mia, 126;  of  St.  Avoid,  127;  Lead-Deposits  of  Mechernich,  127; 
Freihung,  129  ;  Silver  Reef,  Utah,  130 ;  Copper-Deposits  of  New 
Mexico  and  Arizona,  131  ;  Boleo,  Lower  Cal.,  132. 

b.  Metasomatic  Deposits  in  Soluble  Rocks,   .         .     133 

Calamine  Deposits,  134  ;  Laurium,  135  ;  Bohneisenerz  of  Alsace,  136  ; 
Cumberland,  136  ;  Wochein,  Carniola,  136. 

c.  Deposits  in  Crystalline  Schists  and  Eruptive  Rocks,  137 

Taberg,  Sweden,  138  ;  Cornwall,  139  ;  Scandinavia,  140;  Ammeberg, 
141 ;  Prettau  in  Tyrol,  143 ;  Lake  Superior,  144;  Sudbury,  Can.,  14o. 

4.  Hyster 'amorphous  Deposits,         .         .         .         .         .147 

a.  Chemical  effects,      .         .          .         .         .         .148 

Limonite  near  Rio  Tinto,  Spain,  ....        148 

b.  Mechanical  effects,  .          .         .         .         .         .152 

Verchoviky,  Surf  ace- Deposits  in  situ,  152.  Theory  of  the  Sinking  of 
Heavier  Constituents,  153  ;  Stream-detritus,  154  ;  Marine  detritus, 
156 ;  Kackar  District,  Ural  Mountains,  157 ;  Platinum-placers, 
158  ;  Tin-placers,  158. 

c.  Hysteromorphs  of  Older  Geological  Formations,   160 

Deadwood,  S.  Dakota,  160;  Australia,  161;  South  Africa,  162; 
Bohemia,  163. 

INTRODUCTION'. 

ALL  serious  investigators  of  this  problem  .have  recognized  its 
complex  character,  and  the  difficulty  of  solving  it  definitely  in 
the  present  state  of  our  knoAvledge.  Single  and  simple  occur- 
rences are  at  present  clearly  understood;  but  the  more  com- 
plicated phenomena  give  rise  to  discordant  and  often  totally 
contradictory  views,  showing  that  we  are  still  far  from  the 
truth  upon  this  subject.  The  study  of  it  has  been  the  labor  of 
my  life ;  yet  I  must  confess  that  the  little  I  have  here  and  there 
accomplished  bears  no  proportion  to  the  great  range  of  inquiry. 
I  collect,  nevertheless,  in  this  paper,  some  of  the  personal  views 


THE.  GENESIS    OF    ORE-DEPOSITS.  3 

to  which  I  have  been  led,  chiefly  in  order  that  they  may  be 
submitted  for  consideration  and  discussion  to  my  American 
colleagues. 

Looking  upon  a  single,  somewhat  complicated  ore-deposit, 
we  must  confess  that  a  superficial,  tourist's  examination  of  it 
could  not  give  satisfactory  results.  Yet  the  literature  of  this 
subject  refers  us  to  such  materials  chiefly.  Even  treatises  based 
upon  the  profound  studies  of  years  do  not  exhaust  the  subject; 
for  they  are  affected  by  the  existing  stage  of  development  of 
the  auxiliary  sciences,  by  the  existing  degree  of  exploration  and 
exposure  of  the  deposits  described,  and  by  the  personal  views 
of  their  authors. 

Mining,  indeed,  constantly  furnishes  fresh  evidences  in  new 
openings,  but  it  destroys  the  old  at  the  same  time ;  and  if  these 
are  not  preserved  for  science  before  it  is  too  late,  they  are  lost 
forever.  The  whole  mining  industry  is  in  its  nature  transitory ; 
but  the  nation,  \vhich  intrusts  to  the  miner,  upon  certain  con- 
ditions, the  extraction  of  its  mineral  wealth,  has  a  right  to 
demand  that  the  knowledge  thus  gained  at  the  cost  of  a  part 
of  the  national  resources  shall  not  be  lost  to  science. 


PART  I. 
GENERAL  FACTS  AND  THEORIES. 

1.     SYSTEMS  OF  CLASSIFICATION  EMPLOYED  HITHERTO. 

Studies  of  individual  deposits  naturally  involve  speculations 
concerning  their  genesis,  and  many  such  monographs  contain 
valuable  data,  which,  for  the  more  thoroughly  examined  min- 
ing districts,  are  so  well  established  and  so  comprehensive  as 
to  invite  a  systematic  arrangement  and  a  genetic  explanation. 
At  first,  only  the  form  of  the  ore-deposit  was  considered  in 
such  classifications ;  afterwards  the  barren  surrounding  medium 
was  included.  From  this  standpoint,  unfortunately  still  taken 
by  some  purely  empirical  experts,  the  earth's  crust  is  primarily 
divided  into  ore-bearing  and  barren  rocks. 

It  was  especially  the  true  veins,  at  one  time  the  principal  ob- 
jects of  mining,  which  gave  rise  to  speculations  and  discus- 

l 


4  THE    GENESIS    OF    ORE-DEPOSITS. 

sions,  having  now  only  a  historic  interest.*  A.  Werner  was 
the  first  to  frame  a  scientific  theory.  He  distinguished  between 
ore-deposits  contemporaneous  in  origin  with  the  enclosing  rocks 
and  those  of  subsequent  formation,  and  proved  once  for  all 
that  veins  are  fissures  filled  with  ore,  thus  furnishing  the  most 
important  characteristic  for  the  recognition  of  primary  and 
secondary  formations.  As  to  the  manner  in  which  fissures 
have  been  filled,  Werner's  theory,  based  upon  a  comparatively 
limited  field  of  observation,  has,  like  many  of  his  neptunistic 
views,  failed  to  maintain  itself;  and  this  question  remains  still 
without  a  final  answer. 

Curiously  enough,  many  systematizers  reproached  Werner 
for  having  introduced  into  his  system  a  genetic  principle,  which 
they  sought  to  eliminate,  confining  themselves  to  the  form  of 
deposit  as  a  guide.  Thus  Waldenstein  (op.  cit.,  p.  5)  distin- 
guished (a)  tabular  deposits  (beds  and  veins) ;  (6)  stock-deposits, 
flat-lying  or  steeply  inclined ;  and  (c)  scattered  masses,  such  as 
nests  and  pockets. 

Even  Cotta,  otherwise  an  earnest  advocate  of  geological 
principles,  classified  ore-deposits  according  to  their  form  and 
kind  as  beds,  veins  and  masses,  adding  a  new  and  somewhat 
indefinite  group  of  "  impregnations."  J.  Grimm f  also  followed 
in  the  main  the  old  principles  of  classification;  included  in  his 
system  the  eruptive  ore-breccias  which  he  had  personally  ex- 
amined and  the  tabular  segregations  of  ore,  and  pronounced 
not  only  ore-beds  (Erzlager),  but  also  certain  bed-masses  (Lager- 
stocke)  to  be  sedimentary  formations.  Dr.  A.  von  GroddeckJ 
followed  genetic  principles  already  acquiring  predominance. 
He  distinguished :  (a)  original  deposits,  and  (b)  deposits  of  debris. 
The  former  he  subdivided  into  (1)  those  formed  contemporane- 
ously with  the  country-rock,  and  stratified  (ore-beds,  segregated 
beds,  etc.)  or  massive ;  (2)  those  formed  later  (cavity-fillings, 
veins,  cave-deposits,  metamorphic  deposits).  He  pronounced 
ore-beds  (Erzlager)  to  be  sedimentary,  and  included  in  his  sys- 

*  The  period  1556  to  1791,  that  is,  from  G.  Agricola  to  A.  Werner,  is  an  illus- 
tration. See  also  Die  Besonderen  Lagerstdtten  der  Mineralien,  by  J.  Waldauf  von 
Waldenstein,  Vienna,  1824,  p.  164,  etc.  ;  Die  Lehre  von  den  Erzlager statten,  by  B. 
von  Co  ta,  2d  ed.,  Freiberg,  1859,  p.  85,  and  the  English  translation  by  F.  Prime  ; 
and  J.  A.  Phillips'  Treatise  on  Ore-Deposits,  London,  1884,  p.  74,  etc. 

f  Die  Lagerstdtten  der  nutzbaren  Mineralien,  Prague,  1869. 

%  Die  Lehre  von  den  Lagerstdtten  der  Erze.     Em  Zweigder  Geologic,  Leipzig,  1879. 


THE    GENESIS    OF    ORE-DEPOSITS.  5 

tern  the  cave-deposits  and  metamorphic  deposits  without  describ- 
ing their  occurrence  in  detail.  He  declared  that  his  system,  like 
all  others,  had  only  the  purpose  of  arranging  the  material  of 
observation  conveniently  for  comprehensive  study,  and  that 
the  manifold  products  of  nature  could  not  be  forced  into  a 
system  of  classification. 

Groddeck's  description  of  the  series  of  forms  of  deposits  is 
highly  original.  He  presents  a  number  of  types,  mainly  char- 
acterized by  the  varying  material  of  the  deposits  and  its  mani- 
fold combinations  and  transitions.  Evidently  there  was  before 
him  the  ideal  of  combining  in  a  systematic  representation  the 
different  standpoints  from  which  the  subject  was  to  be  viewed. 
At  least,  if  I  correctly  understood  his  personal,  oral  communi- 
cation of  his  views,  he  hoped  to  represent  one  standpoint  by 
abscissae  and  the  other  by  ordinates,  so  that  the  intersection 
would  determine  the  type  of  the  deposit.  This  is  true  enough ; 
but  it  presupposes  an  exhaustive  knowledge  from  both  stand- 
points, which  we  unfortunately  do  not  possess.  My  way  of 
looking  at  the  subject  was,  as  appears  from  his  expressions  in 
a  later  publication,  incomprehensible  to  him.*  It  seemed  to 
him  a  sort  of  heresy  to  doubt  the  contemporaneous  deposition 
of  the  ore  of  the  Mannsfeld  copper-schists  with  the  rock, 
although  I  assured  him  that  this  doubt  need  only  continue 
until  the  chemical  and  physical  possibility  of  such  a  deposition 
should  be  shown. 

Groddeck's  system  comprises,  it  is  true,  the  metamorphic  de- 
posits, but  without  special  definition  or  illustrative  examples. 
In  answer  to  a  criticism  of  A.  Stelzner'sf  on  this  point,  he  re- 
plies that  he  has  included  in  this  class  those  deposits  also 
which  have  been  formed  through  alteration  of  the  rock-ma- 
terial by  the  process  which  Stelzner  had  proposed  to  call  meta- 
somasis,  but  that  the  ore-bearing  masses  thus  originated  cannot 
be  regarded  as  separate  deposits,  because  they  are  only  inci- 
dental phenomena  of  the  filling  of  cavities.  In  other  words, 

*  "Bemerkungen  zur  Classifikation  der  Erzlagerstatten,"  Oesterr.  Zeitschr., 
1885;  Rev.  Univ.  des  Mine*,  1886,  xix. ;  Gornoj  Jour.,  1886,  iii.,  p.  430.  "  Un- 
verstiindlich  1st  es  mir,  dass  Posepny,  der  sich  so  grosse  Verdienste  urn  die 
Kenntnisse  der  Erzlagerstatten  erworben  hat,  das  Vorkommen  sedimentarer  Erze 
ganz  ignorirt,"  etc. 

|  Cited  in  Das  neue  Jahrbuchfilr  Mineralogie,  ii.,  1880,  p.  50. 


6  THE    GENESIS    OF    ORE-DEPOSITS. 

he  grants  but  subordinate  rank  to  one  of  the  clearest  and  most 
important  genetic  aids  to  classification,  furnished  by  the  oc- 
currence of  rocks  transformed  into  ore.  After  conceding  that 
deposits  of  debris  should  probably  be  included  among  strati- 
fied deposits,  he  restricts  his  system  to  four  chief  classes :  1. 
Stratified  or  sedimentary  deposits;  2.  Massive  or  eruptive  de- 
posits; 3.  Cavity-fillings;  4.  Metamorphic  and  metasomatic 
deposits.  This  brings  him  essentially  nearer  to  my  view, 
which  groups  the  first  two  classes  together,  as  contemporane- 
ous with  the  country-rock  in  origin,  with  the  reservation,  how- 
ever, that  the  contemporaneity  indicated  by  the  stratigraphy 
should  be  verified  by  other  evidence. 

While  the  work  of  J.  Grimm  comprises  all  useful  deposits, 
that  of  Groddeck  is  confined  to  ore-deposits,  although  it  would 
be  practicable  to  classify  salt,  coal  and  other  beds  under  his 
system. 

In  England  and  America  the  subject  has  been  variously 
viewed,  considerations  of  practice  being  predominant,  and 
stratification  being  regarded  as  the  specially  decisive  factor. 
This  conception  appears  first,  so  far  as  I  know,  in  the  writings 
of  J.  D.  Whitney,*  who  divides  mineral  deposits  primarily  into 
(1)  superficial,  (2)  stratified  and  (3)  unstratified.  The  strati- 
fied deposits  are  divided  into  (a)  those  in  which  the  valuable 
mineral  constitutes  the  mass  of  a  bed,  (b)  those  in  which  it  is 
disseminated  through  sedimentary  beds,  and  (c)  those  origi- 
nally deposited  from  aqueous  solution,  but  since  metamor- 
phosed. The  unstratified  deposits  are  again  divided  as  irregu- 
lar [subdivided  into  (a)  masses  of  eruptive  origin  (6)  dissemi- 
nated in  eruptive  rocks ;  (c)  stock-work  deposits ;  (d)  contact 
deposits;  (e)  fahlbands]  and  regular  [subdivided  as  (/) 
segregated  veins ;  (g)  gash-veins ;  (h)  true  or  fissure-veins] . 

We  find  here  an  explanation  of  the  term  "  gash-veins," 
unfamiliar  in  Europe.  Whitney  says  (op.  tit.,  p.  225) : 

11  Segregated  veins,  which  are  peculiar  to  the  altered  crystalline,  stratified  or 
metamorphic  rocks,  are  usually  parallel  with  the  stratification  and  not  to  be  de- 
pended on  in  depth.  Gasli -veins  may  cross  the  formation  at  any  angle,  but  are 
peculiar  to  the  unaltered  sedimentary  rocks.  True  veins  are  aggregations  of 
mineral  matter,  accompanied  by  metalliferous  ores,  within  a  crevice  or  fissure, 

*  Report  of  a  Geological  Survey  of  the  Mississippi  Lead  Region,  Albany,  1868,  p. 
224,  and  The  Metallic  Wealth  of  the  United  States,  Philadelphia,  1854,  p.  34. 


THE    GENESIS    OF    ORE-DEPOSITS.  7 

which  had  its  origin  in  some  deep-seated  cause,  and  which  may  be  presumed  to 
extend  for  an  indefinite  distance  downwards." 

Somewhat  different  is  the  classification  of  R.  Pumpelly,* 
who  distinguishes :  I.  Surface-deposits  [(1)  residuary,  (2) 
stream-,  (3)  lake-  and  bog-deposits].  II.  Forms  due  to  the 
texture  of  the  enclosing  rock  or  to  its  mineral  constitution,  or  to  both 
[(1)  disseminated  concentrations,  further  subdivided  as  (a) 
impregnations  and  (6)  fahlbands;  (2)  aggregated  concentra- 
tions, comprising  (a)  lenticular,  (b)  irregular  masses  or  "  stocks," 
(c)  reticulated  veins  or  "  stock-works,"  (d)  contact-deposits] . 
III.  Forms  due  chiefly  to  pre-existing  cavities  or  open  fissures  [(1) 
cave-deposits;  (2)  gash-veins;  (3)  fissure-veins]. 

Dr.  E.  W.  Raymond,t  who  followed,  in  the  main,  the 
classification  of  Lottner,J  distinguished :  I.  Superficial  Deposits 
[(1)  Deposits  of  debris  (placers) ;  (2)  surface-formations  in 
place  (bog-ore,  etc.)].  II.  Inclosed  deposits  [(1)  sheet-formed 
or  tabular,  divided  into  (d)  lodes  or  veins,  and  (b)  beds  and 
seams;  (2)  mass-deposits,  divided  into  (a)  masses,  and  (b) 
impregnations,  etc. ;  and  (3)  other  irregular  deposits,  such  as 
(a)  pockets  distributed  in  large  deposits,  (b)  isolated  segrega- 
tions, gash-veins,  etc.]. 

Prof.  J.  S.  dewberry  §  adheres  mainly  to  the  classification  of 
J.  D.  Whitney,  with  some  new  matter  of  his  own,  the  value  of 
which  has  been  justly  estimated  by  Raymond. || 

An  analogous  line  of  thought  is  followed  by  J.  A.  Phillips.! 
He  declares  that  a  careful  study  of  the  origin,  structure,  and 
composition  of  ore-deposits,  appears  to  justify  their  division 
into  the  following  groups :  1.  Superficial  [(#)  formed  by  the 
mechanical  action  of  waters,  (b)  resulting  from  chemical 
action]  ;  2.  Stratified  [(a)  constituting  the  bulk  of  metalliferous 
beds  formed  by  precipitation  from  aqueous  solutions,  (6)  beds 

*  Not  possessing  the  original  work,  I  quote  from  the  monograph  of  S.  F.  Em- 
mons,  Geology  and  Mining  Industry  of  Leadville,  Washington,  1886,  p.  373. 

f  Report  of  the  Commissioner  of  Mining  Statistics,  Washington,  1871,  and  the  re- 
print, Mines  and  Mining  of  the  Rocky  Mountains,  New  York,  1871,  p.  373. 

J  Bergbaukunde,  Berlin,  1878. 

\  "The  Origin  and  Classification  of  Ore-Deposits,"  School  of  Mines  Quarterly, 
New  York,  March,  1880  ;  also,  Eng.  and  Min.  Journal,  New  York,  vol.  xxix., 
1880,  pp.  421  and  437. 

||  Eng.  and  Min.  Journal,  vol.  xxx.,  1880,  p.  1. 

f  "A  Treatise  on  Ore-Deposits,"  London,  1884,  p.  3. 


8  THE    GENESIS    OF    ORE-DEPOSITS. 

originally  deposited  from  solution,  but  subsequently  altered  by 
metamorphism,  (c)  ores  disseminated  through  sedimentary  beds 
in  which  they  have  been  chemically  deposited]  ;  3.  Unstratified 
\_(a)  true  veins,  (b)  segregated  veins,  (c)  gash-veins,  (d)  impreg- 
nation, (e)  stock-works,  (/)  fahlbands,  (#)  contact-deposits,  (A) 
chambers  or  pockets]. 

In  France,  comparatively  little  has  been  done  in  framing 
such  systems,  higher  importance  being  attached  to  the  syn- 
thesis of  the  minerals,  the  explanation  by  experiment  of 
geological  processes,  and  the  attempt  to  confirm  by  the  study 
of  mineral-deposits  in  other  countries  the  theories  thus  sup- 
ported. Observations  have  been  made  in  many  cases,  not  to 
furnish  material  for  new  conclusions,  but  to  prove  the  truth  of 
existing  theories,  as,  for  instance,  Elie  de  Beaumont's  theory 
of  "  pentagonal  symmetry "  in  the  relation  between  mineral 
veins  and  the  courses  of  mountain  ranges,  etc. 

In  recent  times,  the  chemical  standpoint  has  become  domi- 
nant with  the  French  school,  and  in  the  treatise  of  De  Launay,* 
which  has  just  appeared,  the  attempt  is,  in  fact,  made  to  base 
a  system  of  ore-deposits  upon  a  purely  chemical  view  of  the 
subject.  He  distinguishes :  1,  Gites  d 'inclusions  (ores  as  prim- 
itive constituents  of  eruptive  rocks);  2,  Giles  filoniens  (con- 
taining ores  deposited,  no  matter  how,  in  pre-existing  cavities 
in  the  rocks);  and,  3,  Giles  sedimentaires  (where  metallic  sub- 
stances have  been  laid  down,  either  as  sediments  or  as  precipi- 
tates, in  marine-  or  fresh-water  basins).  In  another  place  I 
will  say  something  of  this  view,  which,  in  some  respects,  cor- 
responds with  my  own. 

It  is  evident  from  the  foregoing  mere  enumeration  of  the 
names  of  groups  and  classes  of  the  several  systems  that,  as  a 
general  rule,  every  new  observation,  considered  important  by 
the  observer,  has  been  added  to  the  established  traditional 
conception,  which,  however,  was  primarily  based  upon  distinc- 
tions of  form  and  kind,  to  which  genetic  principles,  if  recog- 
nized at  all,  were  secondary.  I  may  refer,  in  illustration,  to 
the  class  of  "  pipe-veins,"  and  the  exhaustive  paper  of  Dr. 
Eaymondf  demolishing  it.  I  myself  once  thought  a  new 

*  "Formations  des   Gites   Metalliferes,"    Encydopedie  Scientifique,   des   Aide- 
memoires  publiee  sous  la  direction  de  M.  Leaute,  Paris,  1893. 
f  Trans.  A.  I.  M.  K,  vi.,  1887,  p.  393. 


THE    GENESIS    OF    ORE-DEPOSITS.  9 

group  to  be  warranted  by  conclusive  observations,  namely, 
typhonic  deposits,*  in  which  the  ores  occur  cementing  together 
the  fragments  of  a  brecciated  mass.  But  I  soon  became  con- 
vinced by  the  observation  of  other  occurrences,  equally  difficult 
to  fit  into  the  existing  system,  that  the  whole  system  must  be 
transformed  before  it  coul(J  assimilate,  without  destruction  to 
itself,  the  new  facts  observed  in  the  course  of  time. 

But  a  stable  and  complete  system  could  only  be  framed, 
when  all  the  controlling  facts — in  other  words,  all  the  ore- 
deposits — were  accurately  known.  This  is  not  likely  ever  to  be 
the  case.  New  observations  are  constantly  made  in  mining 
operations,  which,  moreover,  often  obliterate  the  old  ones,  so 
that  they  cannot  be  verified  and  compared. 

It  is,  however,  absolutely  necessary,  in  a  field  so  complicated 
as  that  of  ore-deposits,  to  have  some  general  understanding, 
some  sort  of  system,  comprising  what  is  known.  And  evi- 
dently, in- framing  a  system,  the  characters  of  form,  being  the 
most  obvious  and  the  most  familiar  to  the  miner,  would  be 
naturally  emphasized,  while  genetic  characters  were  left  in  the 
background.  But  this  ought  not  to  check  genetic  investiga- 
tion, or  the  advancing  recognition  of  real  relations.  A  genetic 
system  must,  indeed,  involve  hypotheses,  and  may  not,  for  a 
while,  be  practically  useful;  but  in  time  it  will,  like  every 
other  cultivated  branch  of  geology,  assume  more  permanent 
forms. 

At  the  Przibram  Mining  Academy  there  was  established,  in 
1879,  a  new  chair  of  "  The  Geology  of  Mineral  Deposits," 
which  I  occupied  for  about  ten  years.  As  the  title  indicates, 
it  was  neither  intended  merely  for  instruction  in  the  usual  "sci- 
ence of  mineral  deposits,"  nor  as  a  geological  course,  appended 
to  the  technical  course  in  mining,  as  might  be  inferred  from  a 
title  like  "  Montangeologie"  or  "  Mining  Geology."  The  leading 
subject  in  view  was  the  genesis  of  the  useful  mineral  deposits. 
In  the  present  paper  I  purpose  to  give  a  brief  statement  of  the 
substance  of  my  lectures,  which,  apart  from  a  few  extracts, 
have  never  been  published. 

*  "  Ueber  typhonische  Gesteinsmassen,"  Verh.  d.  k.  k.  geol.  Reichsaust.,  1871, 
p.  94. 


10  THE  GENESIS  OF  ORE-DEPOSITS. 

2.  STANDPOINT  AND  VIEW  OF  THE  PRESENT  PAPER. 

The  principal  genetic  distinction  is  doubtless  between  de- 
posits contemporaneous  with  the  country-rock,  and  those  sub- 
sequently formed  in  it. 

The  earth's  crust  consists  of  rock-elements,  chiefly  individu- 
alized as  mineral  species.  Two  or.  three  dozen  of  them — the 
rock-forming  minerals — constitute  by  far  the  larger  part  of  the 
solid  earth  as  known  to  us.  The  remainder,  much  greater  in 
number  and  variety,  ornament  our  miireral  cabinets,  but  form 
an  insignificant  portion  of  the  rocks.  The  greater  part  of  this 
group  is  made  up  of  the  legion  of  minerals  occurring  in  ore- 
deposits  ;  and  most  of  these  have  undoubtedly  had  a  secondary 
origin  in  the  rocks — for  instance,  all  the  cavity-fillings,  which 
of  course  could  only  be  deposited  after  the  rocks  were  formed. 
The  secondary  origin  of  some  minerals  which  do  not  occur  in 
cavity-fillings  is  less  evident.  But  they  occur  sometimes  in 
company  with  those  which  clearly  have  this  character ;  so  that 
we  may  consider  these  numerous  minerals,  occurring  in  com- 
paratively small  quantities,  as  secondary. 

We  have  two  main  groups  of  mineral  aggregates :  that  of 
the  rocks,  and  that  which  we  will  call  comprehensively  the  min- 
eral deposits.  The  minerals  of  the  first  group  belong  to  it  as 
native  and  original ;  those  of  the  second  are  foreigners  to  the 
rocks  in  which  they  occur.  The  two  groups  may  therefore  be 
designed  (from  tdtos,  one's  own,  and  £&»?,  strange)  as  Idioy- 
enous  and  Xenogenom  respectively. 

It  is  not  necessary  here  to  consider  the  various  origins  of 
rocks,  since  we  take  as  our  starting-point  the  rocks  already 
formed.  The  clearly  sedimentary  rocks  consist  of  the  debris 
of  older  formations — idiogenous  as  well  as  xenogenous ;  and 
we  must  distinguish  in  them,  besides  mechanical  sediments, 
chemical  precipitates  and  organic  products. 

The  sediment  of  a  basin  is  the  detritus  carried  into  it  from 
the  land  and  deposited  in  the  form  of  a  flat  wide  cone.  Suc- 
cessive conical  envelopes  should  therefore  strictly  be  the  form 
of  such  sedimentary  beds,  though  frequently  they  present 
apparently  level  parallel  strata.  The  deposition  of  a  precip- 
itate, on  the  other  hand,  takes  place  throughout  the  liquid  in 
the  basin,  and  its  form  more  completely  represents  the  ideal 
stratum.  In  both  sediments  and  precipitates,  we  find  some- 


THE    GENESIS    OF    ORE-DEPOSITS.  11 

times,  besides  organic  remains,  finely  divided  organic  sub- 
stances, forming  the  bituminous  portions  of  the  rocks.  But 
the  great  masses  of  vegetable  matter  forming  the  coal-beds 
were,  according  to  the  most  widely  held  opinion,  deposited  in 
swampy  bottoms,  and  are  therefore  neither  sediments  nor  pre- 
cipitates. Several  coal-beds,  one  above  another,  indicate  a 
slow  sinking  of  the  basin,  and  its  periodical  filling-up  with 
detritus  from  the  rivers  to  such  an  extent  that  vegetation  could 
again  take  root. 

A  coal-basin  with  several  beds  becomes  on  this  view  the 
measure  of  the  sinking  which  is  doubtless  the  cause  of  every 
large  basin,  but  which  only  becomes  strikingly  evident  when 
the  basin  contains  coal-seams. 

The  foregoing  points  are  mentioned  because  they  indicate 
original  discordances  in  stratification  among  the  sedimentary 
layers  themselves,  and  between  these  and  the  precipitates  and 
organic  formations. 

If  we  find  in  the  midst  of  these  formations  ores  lying  exactly 
between  two  strata,  this  relation  is  not  conclusive  proof  of  their 
sedimentary  or  precipitative  origin.  This  must  be  proved  in 
every  given  case ;  for  in  the  present  state  of  our  knowledge  we 
cannot  understand  how  the  metallic  sulphides  so  characteristic 
of  ore-deposits  could  be  formed  in  that  way. 

As  to  the  eruptive  rocks,  we  do  not  know  what  they  once 
were,  as  we  study  them  only  from  the  moment  of  cooling. 
But  we  observe  at  once  that  iron — a  metal  widely  distributed 
in  ore-deposits  and  in  nature  generally,  occurs  primitive  in 
these  rocks,  in  the  form  of  magnetite,  a  mineral  of  striking 
metallic  appearance. 

This  idiogenite  of  the  eruptive  rocks  can  be  detected  without 
chemical  aid ;  but  with  such  aid  we  find  traces  of  other  metals 
besides  iron ;  and  this  leads  us  to  surmise  that  the  eruptives 
have  brought  a  whole  series  of  heavy  metals  up  from  the 
"  barysphere  "  into  our  "  lithosphere,"  and  that  it  looks  as  if 
the  metals  of  our  ore-deposits  originally  belonged  to  the  bary- 
sphere. This  surmise  De  Launay  regards  as  already  proved. 
He  derives,  as  it  were,  a  priori,  all  the  heavy  metals  of  our 
ore-deposits  from  the  eruptive  rocks,  and  erects  upon  this 
hypothesis  an  entire  system. 


12  THE  GENESIS  OP  ORE-DEPOSITS. 

3.  THE  XENOGENITES  IN  GENERAL. 

With  relation  to  the  xenogenites  or  mineral  deposits,  the  first 
question  concerns  the  space  which  every  secondary  mineral  or 
mineral-aggregate  requires  to  establish  its  existence.  It  must 
either  have  found  this  space  waiting  for  it,  or  it  must  have 
made  room  by  driving  out  an  original  mineral. 

Although  we  shall  chiefly  consider  cavities  formed  in  rocks 
after  the  formation  of  the  rocks  themselves,  we  must  not  forget 
that  some  may  have  been  primitive  in  the  rocks.  We  know 
that  in  substances  of  the  greatest  apparent  density  small  cavi- 
ties or  pores  must  exist,  since  we  can,  for  instance,  by  adequate 
pressure,  force  quicksilver  through  them.  Moreover,  we  en- 
counter in  the  eruptive  rocks  larger  cavities,  suited  to  receive 
considerable  mineral-aggregates — the  so-called  blow-holes. 
These  phenomena  must  certainly  be  considered,  although  the 
cavities  of  secondary  origin  will  first  be  the  subject  of  attention. 

With  regard  to  the  filling,  I  observe,  first,  that  the  mineral 
deposits  upon  the  walls  of  cavities,  from  liquids  circulating 
within  them,  usually  have  a  characteristic  structure,  for  which 
I  propose  the  name  "  crustification,"  as  a  companion  to  "  strati- 
fication." (Single  crusts  were  formerly  called  mineral  shells  or 
scales;  and  Groddeck  introduced  the  word  "crust,"  which  is 
comprehensible  in  most  languages.) 

Most  frequently  mineral  crusts  occur  concentrically  in  regular 
succession,  and  fill  the  whole  cavity  (except  the  central  druse), 
thus  forming  a  symmetrical  crustification.  They  cover,  how- 
ever, not  only  the  cavity-walls,  but  the  surface  of  every  foreign 
body  in  the  cavity,  thus  forming  crusted  kernels  which  greatly 
complicate  the  phenomenon.  We  shall  see,  however,  that  a 
geode-cavity  serves  much  better  than  a  fissure-cavity  to  explain 
the  relations  of  crustification,  and  that  the  crusted  kernels  will 
give  us  no  trouble  in  that  regard. 

Sometimes  mineral  crusts  have  undergone  a  secondary  alter- 
ation (carbonates  are  replaced  with  silica,  etc.).  The  crustifi- 
cation is  thus  made  less  distinct,  or  even  obliterated.  As  a 
general  rule,  however,  crustification  is  a  characteristic  feature  of 
cavity-filling. 

The  cavities  are  formed  either  by  mechanical  or  by  chemical 
forces ;  and  these  two  classes  must  be  sharply  distinguished, 
in  view  of  the  important  role  of  each.  The  former  may  be 


THE    GENESIS    OF    ORE-DEPOSITS.  13 

the  effect  of  exterior  and  foreign  forces,  or  of  such  as  are 
interior,  residing  in  the  rock  itself.  Formerly  I  called  such 
spaces  (with  reference  mainly  to  the  accompanying  fault-phe- 
nomena) "  Spaces  of  Dislocation;"  but  I  believe  the  term 
"  Spaces  of  Discission  "  (from  scindere,  to  tear  apart)  would  be 
more  suitable.  The  latter  class  I  formerly  called  "  Spaces  of 
Corrosion  "  (with  reference  to  the  effect  of  the  leaching  and 
attacking  liquids) ;  but  I  would  now  substitute  the  more  self- 
explanatory  name  "  Spaces  of  Dissolution." 

Spaces  of  dissolution  naturally  occur  in  soluble  rocks,  espe- 
cially limestone,  and  show,  with  wonderful  clearness,  the  irregu- 
lar course  often  followed  by  underground  waters.  At  and  near 
the  surface,  we  often  find  the  cavity-formations  at  the  contact 
of  soluble  with  insoluble  rocks;  and  \ve  may  infer  that  this 
relation  affects  also  the  subterranean  circulation.  Solution 
seldom  extends  to  the  whole  mass  of  the  soluble  rock.  Usually 
it  affects  a  part  only,  in  which  it  forms  more  or  less  irregular 
chains  of  cavities,  sometimes  so  large  that  pieces  of  roof  fall 
in,  and  thus  spaces  of  discission  are  locally  produced.  A  cavity 
filled  with  secondary  mineral,  however  irregular  its  form  may 
be,  and  even  though  it  cuts  across  the  stratification,  usually 
shows  a  predominant  course,  which  wre  are  thus  led  to  recognize 
as  the  channel  of  circulation  of  the  liquid  to  which  we  owe  the 
mineral  deposit. 

As  I  shall  show  later,  we  must  assume  that  the  liquid  which 
formed  the  space  of  dissolution  also  performed  the  filling ;  in 
fact,  that  both  processes  were  almost  contemporaneous.  Nev- 
ertheless, they  must  not  be  confounded  with  the  metamorphic 
processes  where  the  idiogenite  is  expelled,  atom  by  atom,  by 
the  xenogenite;  for  the  deposits  in  spaces  of  dissolution  show 
always  a  distinct  crustification,  and  hence  every  single  crust, 
at  least,  must  have  found  free  space  waiting  for  it. 

Concerning  the  origin  of  spaces  of  discission,  so  much  has 
been  written  that  it  cannot  even  be  stated  in  abstract  here. 
Two  groups  of  these  are  distinguished.  Those  of  the  first 
group  do  not  extend  beyond  one  rock,  and  the  force  which 
produced  them  probably  has  its  seat  in  that  rock..  In  the 
eruptives,  they  are  usually  deemed  fissures  of  contraction;  in 
limes  and  dolomites,  J.  D.  Whitney  called  them  gash-veins. 

The  cavities  of  the  second  group  extend  out  of  one  rock  into 


14  THE    GENESIS    OF    ORE-DEPOSITS. 

another.  The  force  which  produced  them  resided  outside  of 
the  formation.  Considerable  movements  of  one  wall  along 
the  other  are  often  evident,  whence  the  common  name,  "  fis- 
sures of  dislocation." 

In  a  paper  upon  this  subject*,  about  twenty  years  ago,  I 
attempted  to  show  that  every  fissure,  in  whatever  material, 
must  properly  be  a  fissure  of  dislocation ;  that  the  tendency  to 
dislocation  (namely,  an  unequal  tension  in  the  rock)  precedes 
the  formation  of  fissures ;  and  that  whenever  the  condition  of 
the  rock  permits,  a  dislocation  of  the  fissure-walls  can  be  always 
traced,  even  in  fissures  of  contraction. 

As  to  the  filling  of  spaces  of  discission,  it  must  not  be  sup- 
posed, that  they  represent  throughout  their  entire  length  open 
spaces  of  uniform  width.  The  original  fissure  was  sometimes 
closed,  wholly  or  partially,  by  the  detritus  originating  in  the 
friction  of  the  walls,  or  by  the  movement  or  "  swelling  "  of  the 
country-rock,  or  by  other  causes.  Only  the  places  remaining 
open  would  permit  an  active  circulation  of  solutions  and  a 
regular  deposition  from  them.  At  points  obstructed  there 
would  be  no  circulation,  or  a  very  sluggish  one.  When  high 
pressure  was  present,  and  the  rock  contained  interstices,  the 
liquid  doubtless  penetrated  from  the  fissure  into  the  rock,  im- 
pregnating it  with  mineral ;  or  a  soluble  rock  was  attacked, 
and  spaces  of  dissolution  were  formed,  to  be  filled  in  like 
manner  as  the  fissure  itself. 

This  explains  the  fact  that,  on  the  same  vein-plane,  rich  de- 
posits alternate  with  poor  or  barren  spots,  and  that  the  miner, 
seeking  a  bonanza,  persistently  follows  the  barren  traces  of  the 
vein,  according  to  a  well-known,  fundamental  law  of  pros- 
pecting. 

From  the  genetic  standpoint,  the  richer  portions  are  inter- 
esting as  sometimes  occupying  more  or  less  regular  belts  in 
the  vein-plane,  called  "  channels,"  "  shoots,"  "  chimneys,"  etc. 
These  names  evidently  designate  the  main  channels  through 
which  the  mineral  solutions  passed ;  and  the  occurrence  of 
such  forms  in  most  kinds  of  deposits  tends  to  prove  that,  not- 
withstanding other  differences,  they  were  all  formed  in  a 
similar  way. 

*  "Geol.  Betrachtungen  iiber  die  Gangspalten,"  Jahrb.  d.  k.  k.  Bergakademien, 
xxii.,  Vienna,  1874. 


THE    GENESIS    OF    ORE-DEPOSITS.  15 

The  primitive  rock-cavities  (pores  and  blow-holes)  may  also  be 
filled  with  secondary  minerals.  In  the  former,  there  results  a 
finely  disseminated  mineral  substance,  constituting  such  a  deposit 
as  Cotta  denominated  impregnation.  Blow-holes  are  very  often 
filled  with  minerals  of  the  quartz  family  (opal,  chalcedony,  etc.), 
and  we  are  often  able  to  infer  from  the  structure  of  such  geodes 
the  process  by  which  they  were  filled. 

Where  the  mineral  solutions  found  no  cavity  already  pre- 
pared, they  must  have  conquered  the  necessary  place  by  expel- 
ling a  corresponding  part  of  the  original  material.  When  one 
mineral  individual  was  replaced  by  another,  as  in  cases  of 
pseudomorphs,  the  nature  of  the  process  can  often  be  inferred 
from  a  comparison  of  the  composition  of  the  two ;  and  the  laws 
thus  discovered  may  frequently  be  applied  to  the  problems  of 
the  origin  of  mineral  aggregates.  Many  phenomena,  however, 
even  in  the  formation  of  pseudomorphs,  are  hard  to  explain, — 
the  fact,  for  instance,  that  in  some  minerals  the  change  com- 
mences within  the  mass  and  progresses  outward,  etc. 

Where  the  original  material  was  expelled,  there  must  have 
been  first  an  access  for  the  liquids  which  began  and  executed 
this  effect.  Such  may  be  furnished  by  original  minute  rock- 
cavities,  or  by  secondary  cavities. 

The  original  substance  of  the  greater  part  of  the  pseudo- 
morphs known  to  us  was  composed  of  soluble  minerals,  such 
as  carbonates,  sulphates,  and  chlorides,  which  also  occur  as  the 
elements  of  rocks.  Hence  it  may  be  inferred  that  metamor- 
phous  or  metasomatic  deposits  will  be  especially  frequent  in 
soluble  rocks  like  limestone,  dolomite,  etc.,  and  that  we  may 
also  expect  such  deposits  to  occur  frequently  in  company  with 
those  which  fill  spaces  of  dissolution. 

Pseudomorphs  show  us  one  substance  in  the  crystal-form  of 
another.  This  indication  is  lacking  for  the  recognition  of 
metasomatic  deposits;  yet  sometimes  the  original  rock  was 
characterized  by  peculiar  structure,  such  as  lamination  or 
jointing — as,  for  instance,  the  cellular  structure  of  the  Ranch- 
wacke  (Cargneule),  which  is  reproduced  in  the  cellular  calamine 
which  has  replaced  it.  Moreover,  the  original  rock  may  have 
contained  fossils,  which  have  been  replaced,  with  the  rest,  by 
the  new  mineral,  retaining  their  form ;  for  instance,  the  bivalves 
and  mollusks  of  the  Bleiberg  limestone  in  Carinthia  and  at 


16  THE    GENESIS    OF    ORE-DEPOSITS. 

Wiesloch  in  Baden,  reproduced  in  galena  and  calamine ;  the 
brachiopods  of  the  Silurian  iron-ores  of  central  Bohemia,  etc. 

Most  important  for  the  study  of  the  process  are  transitional 
forms  between  the  earlier  and  the  later  material ;  for  instance, 
coatings  of  the  latter  upon  kernels  of  the  former,  such  as 
limonite  upon  siderite  or  ankerite ;  and  likewise  important  is 
the  occurrence  of  regular  pseudomorphs,  replacing  one  element 
in  a  heterogeneous  rock,  like  those  of  cassiterite  after  feldspar 
in  the  granite  of  Cornwall. 

After  the  expulsion,  atom  by  atom,  of  the  original  material, 
the  resulting  deposit  must  be  massive,  showing  no  crustification. 

Frequently,  however,  there  are  only  negative  indications  of 
the  metamorphosis.  It  can  be  seen  merely  that  the  deposit  is 
not  an  original  rock ;  that  it  has  not  been  deposited  in  pre- 
existing primitive  or  secondary  cavities ;  and  hence,  that  it 
must  have  been  formed  by  replacement. 

In  general,  two  kinds  of  metamorphous  deposits  may  be  dis- 
tinguished. In  the  first,  the  new  material  has  replaced  the 
more  soluble  ingredients  of  a  heterogeneous  rock,  and  the  re- 
sult resembles  the  description  of  an  impregnation,  in  which  the 
new  material  occupies  the  original  interstices  of  the  rock.  In 
the  second,  a  part  or  the  whole  of  a  homogeneous  rock  has 
suffered  metamorphosis,  and  the  deposit  will  bear  a  certain 
resemblance  to  filled  cavities  of  dissolution. 

As  I  have  shown  above,  and  will  illustrate  further  on  with 
some  examples,  we  may  thus  establish  certain  types  of  deposits 
entirely  without  reference  to  form.  Some  of  these  may  coin- 
cide with  groups  in  earlier  systems,  but  others  appear  together 
in  one  and  the  same  group.  This  seems  at  first  not  to  favor 
the  practical  usefulness  of  the  above  principles,  but,  as  I  have 
said,  we  do  not  yet  know  enough  to  frame  a  final  system. 
That  must  be  the  aim  of  future  studies,  and  it  is  obvious  that 
our  purely  genetical  factors  will  be  more  helpful  than  the  arbi- 
trary characters  based  upon  the  exterior  form  of  deposits.  We 
distinguish,  then,  Idiogenites,  or  deposits  contemporaneous  in 
origin  with  the  rock,  from  Xenogerdtes,  the  deposits  of  later 
origin,  including  not  merely  those  of  ores,  but  mineral  deposits 
in  general ;  and  to  these  we  may  add,  in  harmony  with  some 
older  systems,  the  deposits  of  debris  as  a  third  class,  Hysterog- 
enites,  or  latest  formations. 


THE    GENESIS    OF.  ORE-DEPOSITS.  17 

The  Xenogenites  we  divide  into  such  as  penetrated  pre-existing 
cavities  (filling  primitive  cavitives,  spaces  of  discission,  or 
spaces  of  dissolution),  and  the  rnetamorphic  or  metasomatic 
deposits,  which  made  room  for  themselves  hy  the  expulsion 
of  an  earlier  material. 

The  form  of  all  these  deposits  is  not  fixed,  but  depends  upon 
various  geological  relations  of  the  country-rock.  The  men- 
tion, under  former  systems,  of  regular  forms  of  deposit,  con- 
templated rather  the  ideal  of  the  system  itself.  In  reality,  the 
ore-bodies  in  "  veins  "  and  "  beds "  are  irregular,  and  form 
masses  for  which  the  most  various  names  exist  in  all  countries. 

We  must  now  speak  more  particularly  concerning  the  method 
of  formation  of  the  different  deposits.  Probably  no  one  doubts 
at  the  present  day  that  they  are  predominantly  the  result  of 
humid  processes  of  solution  and  deposition.  But  such  gener- 
alities are  not  enough.  The  processes  alleged  must  be  put  upon 
the  basis  of  actual  causes,  still  operative,  and  capable  of  being 
proposed  and  discussed  in  explanation  of  geological  phenomena. 
It  is,  therefore,  necessary  to  introduce,  at  this  point,  the  theo- 
retical chapter  which  follows. 

4.  THE  SUBTERRANEAN  WATER-CIRCULATION. 

In  treating  of  the  genesis  of  mineral  deposits,  this  depart- 
ment cannot  well  be  so  lightly  handled  as  it  is  in  most  text- 
books of  general  geology.  Prof.  A.  Daubree,  in  an  authorita- 
tive discussion  of  the  subject,*  ascribes  the  mineral  deposits, 
among  other  effects,  directly  to  the  liquids  circulating  under- 
ground. It  is  my  desire,  with  the  aid  of  personal  observations 
incidental  to  my  continuous  study  of  such  deposits,  to  present  a 
somewhat  closer  view  than  that  of  Prof.  Daubree. 

Surface  phenomena  exhibit  clearly  a  constant  circulation  of 
liquids,  and  corresponding  phenomena,  so  far  as  they  are 
observable  underground,  indicate  the  persistence  of  this  con- 
dition, so  that  we  must  infer  a  subterranean  circulation  con- 
nected with  that  of  the  surface.  We  have  then  to  consider, 
first,  the  surface-phenomena,  so  far  as  they  concern  our  pur- 
pose, and,  second,  the  underground  phenomena. 

As  to  the  former,  we  know  that  it  is  chiefly  the  solar  energy 

*  Les  eaux  souterraines  a  I'epoque  actuelle,  etc.,  vols.  i.  and  ii.,  Paris,  1887  ;  and 
Les  eaux  souterraines  aux  epoques  anciennes,  etc.,  Paris,  1887. 


18  THE    GENESIS    OF    ORE-DEPOSITS. 

which  initiates  the  circulation  by  lifting  above  the  land  the 
water  of  the  sea,  and  thereby  imparting  to  it  the  potential 
energy  which  is  variously  exhibited  in  its  return  to  the  sea, 
The  mechanical  effects  of  flowing  water*  in  erosion,  transpor- 
tation and  sedimentation  need  not  occupy  us  here.  As  to  the 
chemical  effects,  we  know  that  the  mineral  constituents  of  the 
rocks,  dissolved  through  this  circulation,  chiefly  find  their  way 
in  the  rivers  to  the  sea.  In  regions  without  drainage  to  the 
ocean,  the  dissolved  minerals  are  concentrated  by  evaporation, 
which  may  lead  to  precipitation.  I  would  remark,  however, 
that  in  my  opinion  small  proportions  of  salts  are  mechanically 
taken  up  in  the  evaporation  of  sea-water, f  as  careful  analyses 
of  rain-water  have  proved,  and  that  this  fact  leads  to  the  ex- 
planation of  the  salt  and  salt  lakes  in  regions  without  drain- 
age, etc. 

A.    The  Vadose  Underground  Circulation. 

In  connection  with  the  underground  phenomena,  the  ground- 
water  has  for  us  a  special  interest.  As  is  well-known,  a  portion 
of  the  atmospheric  precipitate  sinks,  through  open  fissures  or 
through  the  pores  of  permeable  masses,  into  the  rocks,  and 
fills  them  up  to  a  certain  level.  When  in  a  given  terrain,  by 
wells  or  other  openings,  the  ground-water  (that  is,  the  water- 
level,  Grundwasserspiegel,  nappe  d'eau)  has  been  reached  at 
several  points,  it  is  found  that  these  points  are  in  a  gently  in- 
clined plane,  dipping  towards  the  deepest  point  of  the  surface 
of  the  region,  or  towards  a  point  where  an  impermeable  rock 
outcrops.  The  ground-water  is  not .  stagnant,  but  moves, 
though  with  relative  slowness,  according  to  the  difference  in 
height  and  the  size  of  the  interstitial  spaces,  down  the  plane 
mentioned,  and  finds  its  way,  in  the  first  instance,  directly  into 
the  nearest  surface-stream,  or,  in  the  second  instance,  forms  a 
spring,  which  takes  indirectly  a  similar  course.  Thus  stated, 
free  from  all  complications,  the  phenomenon  exhibits  clearly  the 
law  of  circulation.  The  atmospheric  moisture  evidently  de- 
scends; and  even  the  movement  of  the  upper  layer  of  the 
ground-water  is  only  apparently  lateral,  but  really  downwards, 

*  Die  Wasserfdlle  des  Niagara  und  ihre  geologische  Bedeutung,  by  F.  Posepny, 
Vienna,  1879. 

f  "  Zur  Genesis  der  Salzablagerungen,  besonders  Jener  im  Amerikanischen 
Westen,"  Sitz.  Ber.  der  k.  k.  Accul.  d.  W.  im  Wien,  1877. 


THE    GENESIS    OF    ORE-DEPOSITS.  19 

and  is  determined  (for  equal  sectional  areas  of  the  rock-inter- 
stices) by  the  difference  in  height  between  the  water-level  and 
the  surface-outlet. 

For  that  part  of  the  subterranean  circulation,  bounded  by  the 
water-level,  and  called  the  vadose  or  shallow  underground  cir- 
culation, the  law  of  a  descending  movement  holds  good  in  all 
cases,  even  in  those  complicated  ones  which  show  ascending 
currents  in  parts.  The  total  difference  in  altitude  between  the 
water-level  and  the  surface-outlet  is  always  the  controlling 
factor. 

When  these  two  controlling  levels  are  artificially  changed, 
as  often  happens  in  mining,  the  law  still  operates.  In  sinking 
a  shaft  through  permeable  ground,  it  is  of  course  necessary  to 
lift  continuously  the  ground-water.  The  water-level  thus  ac- 
quires an  inclination  towards  the  shaft,  which  may  thus  receive 
not  only  the  flow  of  the  immediate  vicinity  but  even  also  that 
of  neighboring  valley-systems.  A  shaft  imparts  to  the  pre- 
viously plane  water-level  a  depression,  giving  it  the  form  of  an 
inverted  conoid  with  parabolic  generatrix.  An  adit  produces 
a  prismatic  depression  in  the  water-level ;  and  so  on  for  other 
excavations.  On  the  other  hand,  a  bore-hole,  from  which  the 
water  is  not  removed,  does  not  affect  the  water-level. 

Atmospheric  waters  falling  upon  impermeable  rocks  at  the 
surface  cannot  penetrate  them,  but  must  join  the  existing  sur- 
face-circulation. The  rocks  are  usually  covered  with  more  or 
less  detritus,  in  the  interstices  of  which  the  ground-water  can 
move ;  and  the  water-level  is  in  most  cases  at  the  boundary 
between  the  permeable  surface-formation  and  the  impermeable 
rock  below. 

These  relations  are  complicated  by  the  occurrence  of  fissures 
(which  the  ground-water  of  course  fills),  and  by  the  communi- 
cation of  such  fissures  in  depth  with  permeable  formations, 
which  come  to  the  surface  somewhere  at  a  lower  level,  though 
at  great  distance.  In  such  cases,  as  is  well  known,  a  siphon- 
action  is  set  up,  and  the  ground-water  of  one  region  may  find 
an  outlet  far  away,  even  beyond  a  mountain  range. 

Peculiar  conditions  are  created  by  the  occurrence  of  rela- 
tively soluble  rocks,  such  as  rock-salt,  gypsum,  limestone  and 
dolomite,  in  which,  by  the  penetration  of  meteoric  waters  and 
the  circulation  of  the  ground-water,  connected  cavities  are 

2 


20  THE    GENESIS    OF    ORE-DEPOSITS. 

formed,  constituting  complete  channels  for  the  vadose  circu- 
lation. 

It  is  often  possible  to  observe  directly,  not  only  the  formation 
but  also  the  filling  of  these  cavities,  and  thus  to  obtain  valuable 
material  for  the  explanation  of  the  origin  of  xenogenites  out- 
side the  vadose  circulation,  and  not  observable  in  the  stages  of 
formation. 

It  is  for  our  purpose  a  most  valuable  fact,  that  the  phe- 
nomena of  leaching  indicate  the  path  of  the  circulating  liquids 
through  soluble  rocks,  so  that  we  can  study  the  process  in  its 
several  stages.  The  water  flowing  at  the  bottom  of  a  cave  in 
limestone  is  unquestionably  ground-water;  and  it  follows  that 
the  whole  complex  group  of  cavities  has  been  eaten  out  by  it. 
If  in  another  limestone  cave  we  see  no  flowing  water,  the  cur- 
rent must  have  found  some  lower  outlet ;  and  the  cave  repre- 
sents for  us  an  ancient  ground-water  channel. 

The  many  and  various  phenomena  of  the  Karst  region  are 
well  known :  the  Dolins,  Ponors  and  Katravons — points  where 
a  surface-stream  sinks  into  the  earth ;  vertical  openings,  at  the 
bottom  of  which  flow  subterranean  streams ;  and  caves  out  of 
which  streams  issue — illustrating  the  whole  series  of  the 
entrance,  the  course  and  the  exit  of  subterranean  waters. 

In  1864,  I  had  opportunity  to  observe,  at  Maros  Ujvar,  in 
Transylvania,  a  very  instructive  illustration  of  this  kind,  which 
is  shown  in  Fig.  1.  Here  the  rock-salt  comes  to  the  surface 
with  steep  zigzag  stratification,  and  is  covered  only  with  detri- 
tus, to  the  depth  of  a  few  meters.*  Mining  is  carried  on  in 
great  parallelopiped-shaped  chambers,  by  means  first  of  levels 
run  horizontally  from  a  shaft,  and  winzes  sunk  vertically  from 
these.  The  workings  were  at  that  time  125  meters  or  409  feet 
deep.  A  great  difficulty  in  the  extraction  was  the  entrance  of 
saturated  brine  from  that  side  of  the  mine  where  the  Maros 
river  flowed  by.  Until  the  mine  had  been  protected  by  an  adit 
of  semi-circular  course  in  the  impermeable  rock,  surrounding 
the  salt-body,  the  water  annually  raised  and  delivered  without 
utilization  into  the  river  contained  84,000  tons  of  salt,  or  more 
than  twice  the  weight  of  the  rock-salt  mined. 

*  "Studien  aus  dem  Salinargebiete  Siebenbiirgens,"  by  F.  Posepny,  Ja\rb.  der 
k.  k.  geol.  ReichsansL,  1867,  xviii.,  p.  506-516. 


THE    GENESIS    OF    ORE-DEPOSITS.  21 

Various  investigations  have  proved  that  the  water  of  the 
river  passes  through  the  overlying  detritus  to  the  salt-body, 
which  it  penetrates  at  the  boundary  of  the  impermeable  rock 
of  the  hanging-wall,  finding  its  way  through  separate  channels 
to  appear  as  saturated  brine,  at  the  deepest  point  of  the  mine- 
workings.  These  channels  had  most  frequently  a  cylindrical 
shape,  smooth  walls,  and  sometimes  so  great  a  diameter  that  a 
man  could  crawl  in.  There  were  always  several  to  be  seen,  of 
which,  of  course,  only  the  lowest  in  position  brought  the 
brine. 

The  explanation  is  simple.  The  water  from  the  river,  reach- 
ing the  salt-body  through  the  detritus  cover,  acted  at  the 
border  of  the  salt,  where  the  principal  depressions  in  the  sur- 
face were  located,  and  the  saturated  brine  thus  formed  filled 
all  interstices  in  the  adjoining  salt-body.  By  the  leaching  of 
such  solutions  into  each  deeper  level  opened  in  the  mine,  a  line 
of  maximum  activity  of  circulation  was  gradually  formed, 
which  was  followed  also  by  solutions  not  yet  saturated,  with 
additional  leaching  and  the  final  creation  of  open  channels  as 
the  result. 

An  example  on  a  large  scale  of  such  a  channel  in  rock-salt, 
created,  however,  without  the  aid  of  mining  operations,  was 
recently  described  by  H.  Winklehner,*  who  found  among 
other  striking  phenomena  of  lixiviation  in  the  rock-salt  of  the 
islands  of  the  Persian  Gulf,  a  horizontal  natural  channel  or 
adit,  on  the  island  of  Larak,  which  he  was  able  to  follow  for 
about  1J  kilom.  (1  mile).  It  expanded  in  places  to  caverns  12 
m.  (39  feet)  high,  without  ever  extending  outside  of  the  salt. 

In  precisely  the  same  way  were  formed  the  channels  in  other 
less  soluble  rocks,  such  as  limestone,  when,  the  level  of  the  en- 
trance being  above  that  of  the  exit  of  the  ground-water,  a  line 
of  maximum  activity  of  circulation  was  established  between  the 
two  points.  This  line,  and  the  cavities  developed  along  it, 
would  not,  indeed,  always  have  the  regular  parabolic  course, 
but  would  be  dependent  upon  various  influences  of  the  stratifi- 
cation, the  presence  of  rocks  of  unequal  solubility,  or  even  an 
intermixture  of  impermeable  rocks.  A  mass  of  the  latter,  oc- 

*  "  Salzvorkommen  in  Siid-Persien,"  Oesterr.  Z.  fur  Berg-und  Hiittenwesen,  1892 
xl.,p.  581. 


22  THE    GENESIS    OF    ORE-DEPOSITS. 

curring  on  the  line  connecting  the  two  points  named,  might 
cause  the  channel  to  bend  up  and  down,  or  even  in  places  to 
assume  an  upward  inclination. 

Figs.  2  and  3  illustrate  these  conditions.  S  is  the  soluble,  I 
the  impermeable  rock;  a,  the  entrance-point  and  z  the  outlet- 
point  of  the  ground-water;  a  b  c  z,  the  line  along  which  ap- 
proximately a  channel  might  be  made,  if  the  impermeable  rock 
were  not  present.  In  its  presence,  the  dissolving  current  must 
take  another  road,  a  d  z,  following  more  or  less  the  contact  be- 
tween S  and  I,  and  in  Fig.  2,  descending  to  a  depth  propor- 
tioned to  the  relation  between  the  original  rock-interstices  and 
the  hydrostatic  head,  while  in  Fig.  3  it  first  surmounts  the  dam 
formed  by  the  impermeable  rock,  and  then  plunges  towards 
the  outlet  z.  We  see  that  in  this  wray  various  channels  may 
originate  at  the  contact  of  permeable  and  impermeable  rocks, 
as  indeed  we  find  them  often  in  nature. 

But  when  to  these  factors  fissures  are  added,  the  conditions 
are  essentially  changed,  for  the  circulation  follows  in  preference 
the  open  fissures,  and,  if  they  pass  through  soluble  rocks,  en- 
larges them  by  solution. 

Sometimes  the  position  and  the  level  of  the  outlet  are  altered 
— as,  for  instance,  in  the  progressive  erosion  of  valleys  ;  and  it 
may  then  easily  happen  that  the  new  channel,  representing  the 
new  conditions,  will  take  a  totally  different  direction,  crossing 
the  line  of  the  old  one. 

Siphon-action  is  to  be  observed  in  soluble,  much  more  fre- 
quently than  in  permeable  rocks,  as  the  frequency  of  intermit- 
tent springs  in  limestone  indicates.  Such  springs  presuppose 
the  existence  of  a  siphon-like  channel,  through  which  the 
ground-water  cannot  flow  to  escape  from  the  lower  leg  until 
the  water-level  has  risen  to  the  top  of  the  bend  of  the  siphon. 

We  have  seen  that  the  ground-water  may  traverse  deep  fis- 
sures leading  to  soluble  or  permeable  rocks,  and  may  follow 
such  rocks  for  considerable  distances.  When  the  ground-water, 
warmed  in  depth,  has  an  opportunity  to  reach  the  surface,  such 
as  is  given  in  Fig.  6  by  the  difference,  H,  in  level,  a  thermal 
spring  is  the  result — a  so-called  acrotherm,  if  its  water  is  not 
highly  charged  with  minerals,  and. not  unlike  the  ground-water 
of  the  place. 

Artesian  wells  present  an  analogous  case,  also  explained  hither- 


THE    GENESIS    OF    ORE-DEPOSITS.  23 

to  by  the  principle  of  hydrostatic  pressure  (see  Fig.  7).  The 
outcrop  of  the  permeable  layer  has  been  assumed  to  be  neces- 
sarily higher  than  the  mouth  of  the  well,  in  order  to  account 
for  the  rising  of  the  water  above  the  latter  level.  The  cause 
has  been  conceived  as  the  operation  of  communicating  pipes, 
the  drill  hole  being  one  leg,  and  the  permeable  layer  the  other, 
and  it  has  been  overlooked,  that  the  latter  is  no  open  pipe,  but 
a  congeries  of  rock-interstices,  in  which  the  water  has  to  over- 
come a  great  resistance,  and  that,  perhaps,  in  level  regions  no 
hydrostatic  head  at  all  can  be  demonstrated.  Certainly  the 
powerful  factor  of  the  higher  temperature,  and  in  some  cases 
the  gaseous  contents,  of  the  ascending  water,  were  omitted 
from  the  calculation. 

It  would  be  a  matter  of  surprise  to  me,  if  the  purely  hydro- 
static and  strictly  mathematical  views  heretofore  current  on 
this  subject  had  not  led  to  disappointment.  I  introduce  Fig.  7, 
the  conventional  diagram  of  an  artesian  well,  for  the  purpose 
of  stimulating  further  thought  on  the  matter. 

The  Filling  of  the  Open  Spaces  Formed  by  the  Vadose  Circula- 
tion.— This  is  very  important  genetically,  since  it  is  a  matter 
subject  to  current  and  direct  observation,  and  capable  of  fur- 
nishing conclusions  applicable  to  inaccessible  subterranean 
occurrences. 

We  can  observe  spaces  on  the  bottom  of  which,  frequently, 
the  ground-water  which  excavated  them  is  still  flowing,  and 
which  are  therefore  filled  for  the  most  part  with  air.  Liquids 
carrying  various  minerals  drip  into  these  spaces  and  leave  a 
part  of  their  contents  on  the  walls;  the  cause  of  deposition 
being,  on  the  one  hand,  the  evaporation  of  a  part  of  the  liquid, 
or,  on  the  other  hand,  such  changes  as  the  loss  of  carbonic  acid, 
precipitating  as  carbonate  the  soluble  bicarbonate  of  lime ;  the 
oxidation  of  soluble  ferrous  to  insoluble  ferric  oxide ;  the  re- 
duction of  ferrous  sulphate  by  organic  matter  to  sulphide,  etc. 
The  form  and  structure  of  these  precipitates  vary  at  different 
parts  of  the  walls.  On  the  roof  occur  the  stalactites,  and  on  the 
floor  (if  it  be  not  covered  with  water)  the  corresponding  stalag- 
mites. The  wall-deposits  have  characteristic  forms  likewise ; 
so  that  we  can  recognize  by  the  appearance  of  any  piece  of 
the  deposited  mineral  the  place  where  it  was  formed.  But 
from  water  covering  the  bottom  of  the  cavity  only  horizontal 


24  THE    GENESIS    OF    ORE-DEPOSITS. 

deposits  can  orginate.  Sometimes  the  cavity  is  contracted,  so 
that  its  whole  cross-section  is  occupied  by  the  liquid.  If  it  is 
accessible  to  observation,  we  can  then  see  that  the  deposits 
from  the  circulating  liquid  cover  the  walls  uniform^. 

This  can  be  much  more  clearly  observed  in  artifical  conduits, 
where  precipitation  occurs.  We  find,  for  instance,  in  the  pipes 
which  convey  concentrated  brine,  the  walls  uniformly  covered 
with  a  deposit,  mostly  of  gypsum.  But  if  air  or  gas  is  admit- 
ted into  the  pipes,  the  deposit  occurs  only  at  the  bottom.  We 
may  thence  infer  that  so  long  as  the  circulating  liquid  fills  the 
whole  cavity  the  attraction  of  the  walls  for  the  precipitated 
particles  is  controlling ;  but  that  when  gas  enters,  gravity  be- 
comes predominant  and  draws  these  particles  to  the  bottom. 

In  opal  and  chalcedony  geodes  we  can  often  see  both  forms 
of  precipitate  :  the  crust  uniformly  covering  the  walls,  and  the 
horizontal  deposit.  Fig.  4  represents  a  geode  of  iron-opal, 
from  Dreiwasser,  in  Hungary,  in  which,  besides  the  crustifica- 
tion  and  horizontal  deposit,  stalactitic  and  stalagmitic  forms  also 
appear.  A  thin  crust  of  translucent  hyalite  covers  all  parts  of 
the  wall,  including  the  floor.  The  cylindrical  stalactites  are  also 
of  hyalite.  Some  of  them  extend  to  the  bottom,  and  are  per- 
haps joined  to  stalagmites  rising  from  the  crust  there.  The  re- 
maining space  is  half  filled  with  a  milk-white,  opaque,  opaline 
substance,  in  which  occurs  a  thin  layer  of  translucent  hyalite. 
On  the  same  specimen  several  other  less  regular  cavities  are 
visible.  All  of  them  were  lined  with  the  hyalite  crust,  and 
some  have  also  the  opaline  layers.  These  layers  are  parallel 
in  all  the  cavities ;  and  it  cannot  be  doubted  that  they  were 
horizontally  deposited.  The  stalagmites  stand  at  right  angles 
to  them,  and  were  unquestionably  vertical  when  formed.  The 
geode  certainly  occupied,  therefore,  at  the  place  of  formation, 
the  position  shown  in  Fig.  4. 

I  must  resist  the  temptation  to  describe  the  manifold  forms 
of  deposit  in  limestone  caves.  Fig.  5,  an  ideal  diagram,  show- 
ing a  wall-accretion,  and  stalactites  and  stalagmites,  separate 
and  grown  together,  is  given,  not  to  illustrate  the  variety  of 
the  phenomena,  but  to  indicate  their  analogy  with  those  of  the 
little  geode  in  the  iron-opal  of  Fig.  4.  It  is  easy  to  conceive, 
that,  under  some  circumstances,  particularly  in  old  cavities, 
lying  above  the  water-level  and  not  subject  to  further  enlarge- 


THE    GENESIS    OF    ORE-DEPOSITS.  25 

ment,  the  formation  of  stalactites,  etc.,  might  ultimately  fill 
the  whole  space. 

The  floor  of  caves  often  shows  deposits  colored  with  ferric 
oxide,  the  explanation  of  which  is  obvious.  Sometimes  we 
find  in  the  upper  caves  traces  of  sediments  also ;  and,  in  one 
instance  I  found  in  an  outlet-cave  pebbles  of  very  hard  rocks, 
which  certainly  came  from  the  surface.*  The  chemical  reac- 
tion of  the  formation  and  filling  of  these  caves  are  so  simple 
as  to  need  no  discussion  here. 

Much  more  various  observations,  however,  can  be  made  in 
the  artificial  caves,  formed  by  mine-workings.  Here  we  have 
conditions  analogous  to  those  of  the  natural  caves,  but  much 
greater  variety,  since  the  most  widely  different  substances  come 
into  play.  The  mine-workings  are  situated  at  an  artificially 
depressed  water-level,  and  will  show,  in  general,  processes 
analogous  to  those  observed  in  limestone  caves,  particularly 
the  formation  of  stalactites.  From  calcareous  rocks,  from 
mineral  deposits,  and  from  the  mine-masonry,  crusts,  stalac- 
tites and  sinter  are  formed,  analogous  to  those  which  occur  in 
cavities  at  the  natural  water-level.  Processes  of  oxidation  will 
here  also  play  the  leading  part,  although  reduction  may  also 
be  effected  through  the  more  abundant  organic  matter  in  the 
mine-waters.  Thus  stalactites  of  pyrites,  evidently  reduced 
from  ferrous  sulphate  by  organic  matter,  are  often  found  in 
metal-mines.  A  respectably  large  number  of  observations 
already  illustrates  the  processes  which  are  going  on  under  our 
eyes  in  mines,  and  from  which  we  can  draw  conclusions  as  to 
the  destruction  and  creation  of  many  minerals  by  circulating 
under-ground  solutions.  But  we  must  not  forget  that  these 
proofs  apply  only  to  the  conditions  of  the  shallow  or  vadose  cir- 
culation, and  that,  for  the  explanation  of  the  formation  of  the 
more  ancient  deposits,  we  must  look  to  the  rock-regions  below 
the  water-level. 

In  order  to  give  at  least  one  American  example,  I  refer  to 
the  observation  of  Raymond,  who  found  in  an  old  Spanish 
mine,  in  the  Cerillos  range  of  New  Mexico,  an  iron  pick-axe, 
the  eye  of  which  was  filled  with  beautifully  crystallized  galena, 

*  ''Geol.  mont.  Studie  der  Erzlagerstiitten  von  Rezbanya  in  S.  O.  Ungarn," 
von  F.  Posepny,  Ung.  geol.  Gesellsch.,  1874,  p.  48. 


26  THE    GENESIS    OF    ORE-DEPOSITS. 

evidently  a  reduction  of  lead  sulphate  by  the  decaying  wood 
of  the  handle  of  the  pick.* 

It  may  be  said,  in  general,  that  the  results  of  the  processes  of 
oxidation,  chlorination,  and  reduction,  observed  in  those  re- 
gions of  ore-deposits  which  lie  above  water-level,  have  come  to 
pass  under  conditions  analogous  to  those  just  described;  so 
that  we  are  able  to  adduce  extended  series  of  proofs,  not  only 
as  to  formations  now  going  on,  but  also  a's  to  similar  formations 
long  since  finished. 

B.    The  Deep  Underground  Circulation. 

Thus  far,  we  have  considered  only  such  processes  as  take 
place  in  the  region  above  water-level,  and  are  still,  in  some 
cases,  open  to  our  observation.  As  we  descend  to  a  deeper  re- 
gion, there  is  less  hope  of  encountering  formative  processes 
still  active.  When  we  penetrate  by  mining  into  the  depths, 
we  artificially  depress  the  water-level,  and  create  conditions 
unlike  those  which  attended  the  formation  of  the  deposits. 

But,  if  we  compare  the  deposits  formed  below  water-level, 
under  proportionally  greater  pressure  and  at  higher  tempera- 
ture, with  those  of  the  upper  region,  it  appears  beyond  doubt 
that  the  former  also  must  have  been  produced  by  deposition 
from  fluid  solutions. 

When  we  compare  the  low  solubility  of  certain  ingredients 
of  the  deposits  with  the  spaces  in  which  they  occur,  often  in 
large  quantity,  it  is  impossible  to  assume  that  they  could  have 
been  precipitated  from  solutions  existing  in  these  spaces  only. 
We  must  concede  that  immense  volumes  of  solutions  must 
have  flowed  through  the  spaces — in  other  words,  that  the  de- 
posits were  precipitated  from  liquids  circulating  in  these  chan- 
nels. 

The  formation  of  these  cavities  has  been  already  discussed, 
and  referred  to  mechanical  and  chemical  causes.  It  remains 
to  consider  the  manner  of  their  filling.  We  have  seen  that 
the  uppermost  layer  of  the  ground-water  has  an  apparently 
lateral,  but  really  descending  movement ;  and  it  is  very  natural 
to  imagine  that  this  top  layer  slides,  as  it  were,  upon  a  lower 
mass,  which  is  apparently  stagnant.  According  to  this  con- 

*  Trans.  A.  L  M.  E.,  1883,  xi.,  p.  120. 


THE    GENESIS    OF    ORE-DEPOSITS.  27 

ception,  the  deep  region  would  be  comparable  to  a  vessel  filled 
with  various  permeable,  impermeable,  and  soluble  materials, 
over  which  water  is  continually  passed,  so  that,  from  the 
moment  when  all  the  interstices  have  been  once  filled,  only 
the  uppermost  water-layer  has  any  movement. 

But,  with  increase  of  depth,  the  pressure  of  the  water-column 
increases,  as  does  the  temperature.  The  warm  water  certainly 
tends  to  rise,  if  not  prevented  by  interstitial  friction,  as  is,  no 
doubt,  generally  the  case.  But  where  the  warmed  water  finds 
a  half-opened  channel  communicating  with  the  upper  region, 
it  will  experience  much  less  friction  on  the  walls,  and  must 
evidently  ascend.  It  might  thus  be  conceived  that  the  ground- 
water  descends  by  capillarity  through  the  rock-interstices  over 
large  areas,  in  order  to  mount  again  through  open  channels  at 
a  few  points. 

This  subject  was  viewed  by  A.  Daubree  in  a  much  wider 
significance,  and  extended  to  cover  the  origin  of  volcanic  phe- 
nomena.* He  propounded  the  inquiry,  whether  the  enormous 
quantities  of  steam  which  are  daily  liberated  from  the  deeper 
region  are  continually  replaced  from  the  surface,  and  if  so, 
how  ?  He  pointed  out  that  this  water-supply  could  not  take 
place  through  open  fissures,  in  which  the  liquid  water  de- 
scended at  one  time  and  the  steam  ascended  at  another,  but  he 
showed  that  the  descent  could  be  effected  through  the  porosity 
and  capillarity  of  the  rocks.  Jamin's  experiments  have  taught 
us  the  influence  of  capillarity  upon  the  conditions  of  the  equi- 
librium established  by  means  of  a  porous  body  introduced  be- 
tween two  opposing  columns.  Daubree  constructed  an  appa- 
ratus in  which  the  temperature  in  one  part  of  the  capillary 
passage  was  so  high  that  the  liquid  must  assume  the  form  of 
steam,  and  thus  escape  the  operation  of  the  laws  governing  its 
infiltration.  This  apparatus  comprised  a  sandstone  slab,  with 
water  above  and  a  chamber  below,  the  latter  provided  with  a 
manometer  for  measuring  the  pressure  of  the  steam  collected  in 
it.  The  whole  was  exposed  to  a  temperature  of  about  160°  C. 
(320°  F.),  and  steam  collected  in  the  chamber  of  68  cm.  mer- 
cury-column, indicating  about  13  pounds  over  the  atmospheric 
pressure  in  the  manometer,  or  a  total  pressure  of  about  1.9  at- 

*  Synthetische  Studien  zur  Experimentalgeoloyie,  by  A.  Daubrfee  ;  German  transla- 
tion, by  Dr.  A.  Gurlt,  Brunswick,  1880,  p.  180. 


28  THE    GENESIS    OF    ORE-DEPOSITS. 

mosphere.  This  steam  could  only  come  from  the  water  above 
the  sandstone  through  which,  in  spite  of  the  pressure,  a  capil- 
lary filtration  took  place. 

"  The  difference  in  pressure  on  the  two  sides  of  the  stone  not  only  did  not  drive 
the  liquid  back,  but  permitted  it  to  filter  quickly  from  the  colder  side  (100°  C.  = 
212°  F.)  to  the  hotter  (160°  C.  =320°  F.),  and  favored  the  rapid  evaporation  and 
the  drying  of  the  hot  stone  surface"  (np.  cit.,  p.  184). 

"According  to  these  experiments,  therefore,  water  may  be  found  by  capillarity, 
operating  in  the  same  direction  as  gravity,  against  a  strong  interior  counter-pres- 
sure, to  descend  from  the  shallower  and  cooler  regions  to  deeper  and  hotter  ones, 
where,  by  reason  of  acquired  temperature  and  tension,  it  is  capable  of  producing 
great  mechanical  and  chemical  effects"  (op.  cit.,  p.  186). 

Daubree's  experiment  confirms  our  view  that  the  portion  of 
the  ground-water  lying  below  water-level  is  not  stagnant,  but 
descends  by  capillarity,  and  since  it  cannot  be  simply  consumed 
in  depth,  receives  there  through  a  higher  temperature  a  ten- 
dency to  return  towards  the  surface,  which  tendency  is  most 
easily  satisfied  through  open  channels.  Stated  summarily:* 
The  ground-water  descends  in  the  deep  regions  also  through 
the  capillaries  of  the  rocks ;  at  a  certain  depth  it  probably 
moves  laterally  towards  open  conduits,  and,  reaching  these,  it 
ascends  through  them  to  the  surface. 

The  solvent  power  of  the  water  increases  with  temperature 
and  pressure,  and  also  with  the  duration  of  its  underground 
journeying.  Hence,  while  it  is  descending,  it  can  dissolve  or 
precipitate  only  the  more  soluble  substances.  But  the  ascend- 
ing current  in  the  open  conduits  is  undoubtedly  loaded  more 
heavily  and  with  less  soluble  substances,  which,  as  the  con- 
ditions of  their  solubility  (temperature  and  pressure)  gradually 
disappear  in  the  ascent,  must  be  deposited  in  the  channels 
themselves. 

The  open  channels,  in  which  the  solutions  ascend,  are  not 
the  deductions  of  theoretical  speculation.  They  really  exist,  as 
we  can  prove  by  induction  from  appropriate  observations. 

The  Ascending  Waters  Encountered  in  Mines. — A  number  of 
such  phenomena  are  adduced  by  H.  Miiller.f  For  instance,  in 

*  Ueber  die  Bewegungsrichtung  der  unterirdisch  circulirenden  Fliissigkeiten,  von  F. 
Posepny.  Extrait  du  compte  rendu  de  la  3me.  session  du  Congres  geologique  interna- 
tional. Berlin,  1885,  p.  71. 

t  "Ueber  die  Beziehungen  zwischen  Mineralquellen  und  Erzgangen."  Cotta's 
Gangstudien,  vol.  iii.,  1860,  p.  261. 


THE    GENESIS    OF    ORE-DEPOSITS.  29 

the  Gottes  Geschick  mine,  near  Schwarzenbach,  in  the  Erzge- 
birge,  at  the  depth  of  110  rn.  (360  feet)  an  acid  spring  contain- 
ing C02  and  H2S  emerges  from  a  nickel-  and  cobaltiferous-silver 
ore-vein  (op.  cit.,  p.  286).  At  the  "Wolkenstein  Bad,  an  acid 
spring  comes  from  the  druses  of  an  ore-vein  containing  a  crust 
of  barytes  and  amethyst.  In  the  Alte  Hoffhung  Erbstollen 
mine,  near  Mitweida,  bad  air  and  exhalations  of  carbonic  acid 
led,  in  1835,  to  an  analysis  of  the  ground-water,  which  proved 
to  be  weakly  acid.  In  the  Churprinz  mine  at  Freiberg  a  warm 
(25°  C.  =  77°  F.)  acid  spring  was  struck  on  the  Ludwig  Spat 
vein  at  the  depth  of  about  160  m.  (525  feet).  Besides  these, 
Miiller  names  a  number  of  mineral  springs  occurring  in  Bohe- 
mia and  Saxony  at  the  outcrops  of  mineral  veins  never  opened 
by  mining.  In  spite  of  the  great  reserve  which  he  exhibits,  he 
summarizes  his  view  as  follows  (op.  tit.,  p.  307); 

"  Mineral  veins  and  mineral  springs  are  certainly  adapted  to  complement  each 
other  in  genetic  theory.  On  the  one  hand,  the  ore-veins,  as  extended,  indefi- 
nitely deep  fissures,  gradually  filled,  indicate  a  very  profound  origin  for  the  min- 
eral springs,  and  suggest  variations  caused  by  time  and  circumstances  in  the 
amount  and  mutual  reactions  of  their  contents,  solid  or  volatile  ;  and,  on  the  other 
hand,  the  present  relations  of  mineral  springs  explain  the  mode  of  ingress  and 
deposit  of  the  constituents  filling  the  veins." 

Soon  after  this  publication  (I  think  in  1864),  a  thermal 
spring  of  23°  C.  (73°  F.)  was  struck  at  a  depth  of  533  rn.  (1748 
feet)  in  the  Einigkeit  shaft,  at  Joachimsthal,  and  in  the  same 
mine  at  two  other  points  similar  mineral  springs,  rising  with 
strong  pressure,  were  exposed.  They  prevented  further  in- 
crease in  depth  of  that  part  of  the  mine,  and  were  plugged  as 
far  as  practicable.  The  analysis  made  in  1882  showred  that 
they  were  acid  springs  containing  considerable  silica  (33 
grammes  per  ton).  In  one  of  them  arsenic  was  also  proved 
to  the  extent  of  22  grammes  per  ton.* 

The  mineral  waters  of  the  Joachimsthal  mines  are  said  to 
come  in  contact,  near  the  place  where  they  were  encountered, 
with  basalt-like  rocks  (called  Wackeri),  which  traverse  the  ore- 
veins,  and  are,  therefore,  of  later  origin.  In  general,  most  of 

*  Since  the  metric  ton  of  1000  kilo.,  or  the  weight  of  m.3  (1  cubic  meter)  of 
water,  is  a  rational  unit  of  weight,  I  refer  all  tenors  to  it,  and  state  them  in 
grammes  or  milligrammes  to  avoid  decimals.  Thus  22  grammes  per  ton  repre- 
sents 0.022  per  thousand,  or  0.0022  per  cent. 


30  THE    GENESIS    OF    ORE-DEPOSITS. 

the  ore-deposits  of  the  Erzgebirge  appear  to  have  a  decidedly 
recent  origin,  but  even  from  this  standpoint  the  mineral  springs 
found  in  mining  are  to  be  regarded  as"  nothing  else  than  the 
continuation  of  those  ascending  liquids  which  have  filled  the 
ore-veins.  Mining  depresses  the  water-level,  so  that  mineral 
waters  circulating  in  the  neighborhood  are  forced  to  those 
points  in  the  mine  where  there  is  only  atmospheric  pressure. 

This  "  neighborhood "  may,  indeed,  extend  to  a  compara- 
tively long  distance.  For  instance,  the  thermal  spring  at  Carls- 
bad, which  is  the  nearest  to  Joaehimsthal,  is  17  kilom.  (10.5 
miles)  away  and  380  m.  (1246  feet)  above  sea-level,  while  the 
spring  in  the  Einigkeit  shaft  at  Joachimsthal  was  struck  at 
206  m.  (675  feet)  above  sea-level,  that  is,  174  m.  (571  feet)  lower 
than  Carlsbad.  The  irruption  of  the  thermal  waters  of  Teplitz 
in  Bohemia  into  the  lignite-mine  of  Dux,  7  kilom.  (4  miles) 
away,  which  took  place  first  in  1879,  and  has  occurred  re- 
cently since,  shows  plainly  that  subterranean  communications 
may  thus  be  established  for  long  distances  by  mining,* 

Additional  data  for  the  study  of  these  relations  are  furnished 
by  the  miners  on  the  Comstock  lode,  where,  with  the  advan- 
cing depth  of  operations,  ascending  thermal  waters  were  un- 
expectedly encountered,  the  abundance  and  high  temperature 
of  which  presented  extraordinary  obstacles  to  mining.  The 
great  richness  of  the  deposit  was  the  reason  that  the  hope  of 
going  deeper  was  not  abandoned,  as  in  Joachimsthal,  where 
the  only  effort  was  to  dam  out  the  waters  from  existing  work- 
ings ;  but  that,  on  the  contrary,  the  struggle  was  accepted 
against  the  waters  themselves  and  the  enormous  heat  which 
they  caused  in  the  mines. 

As  is  well  known,  the  upper  workings  on  the  Comstock,  be- 
fore any  ascending  waters  had  been  encountered,  were  not 
specially  hot,  though  warmer  (21°  to  24°  C.,  or  70°  to  75°  F.) 
than  other  mine-workings  in  similar  positions.  Dr.  F.  Baron 
v.  Richthofen  noticed  no  abnormal  mine-temperature,  although 
he  ascribed  the  Comstock  to  earlier  solfataric  action,  f 

* 

*  "  Einige,  die  Wassereinbriiche  in  die  Duxer  Kohlenbergbaue  betreffende, 
geologische  Betrachtungen,"  von  F.  Posepny.  Oesterr.  Zeitsch.  f.  Berg-u.  Huttemv., 
1888,  xxxvi.,  pp.  39-54. 

f  The  Comstock  Lode,  Its  Character  and  Probable  Mode  of  Continuance  in  Depth, 
§an  Francisco,  1866,  p.  54. 


THE    GENESIS    OF    ORE-DEPOSITS.  31 

At  a  later  period,  upon  the  cutting  through  of  clay-partings 
in  the  rock,  the  hot-water  repeatedly  broke  into  the  workings 
with  great  force,  as,  for  instance,  in  the  North  Ophir  mine, 
when,  according  to  Clarence  King,*  the  workmen  had  scarcely 
time  to  escape.  The  water  is  said  to  have  had  a  temperature 
of  40°  C.  (104°  F.),  and  filled  the  workings  immediately  to  a 
height  of  30  m.  (100  feet).  In  another  case  the  water  broke 
into  the  2200-foot  level  of  the  Savage  mine,  and  filled  the  large 
spaces  both  of  that  mine  and  of  the  Hale  and  Norcross  up  to 
the  1750-foot  level,  or  to  a  height  of  137  m.  (450  feet).  Gas 
was  continually  but  not  violently  evolved ;  and  although  Prof. . 
J.  A.  Churchf  reports  it  to  have  been  under  a  pressure  of  200 
pounds  per  square  inch,  he  believes  that  this  was  not  a  gaseous, 
but  a  hydrostatic  pressure. 

The  water  which  in  1880  flooded  the  Gold  Hill  mines  came 
from  a  bore-hole  in  the  Yellow  Jacket  shaft,  at  a  depth  of  939 
m.  (3080  feet);  had,  according  to  George  F.  Becker,!  a  tem- 
perature of  77°  C.  (170°  F.) ;  and  was  heavily  charged  with 
hydrogen  sulphide.  In  the  upper  levels  of  the  mine,  Becker 
says  there  is  evidence  of  the  presence  of  carbonic  acid,  and  on 
the  2700-foot  level  where  the  temperature  was  66°  C.  (150°  F.) 
a  deposit  of  sinter  was  found,  consisting  mainly  of  carbonates. 
Church  (p.  206)  remarks  that  it  was  at  first  believed  that  the 
repeated  irruptions  of  water  came  from  chains  of  cavities  exist- 
ing in  the  rock,  but  that  at  the  time  of  his  visit  the  conviction 
was  that  they  came  through  shattered  and  decomposed  seams, 
parallel  with  the  lode,  and  sometimes  of  great  thickness. 

Systematic  and  long-continued  temperature-observations  in 
several  Com  stock  mines  enabled  Becker  to  represent  compre- 
hensively for  different  lines  the  increase  of  temperature  with 
depth  ;  and  it  thus  appeared  that  this  increase  was  greatest  in 
the  vicinity  of  the  lode,  diminishing  with  the  distance  from 
the  lode ;  that  the  vehicle  of  heat  was  the  water ;  and  hence 
that  it  was  through  the  lode  itself  that  communication  with 
the  hot  depths  took  place,  and  the  phenomenon  denominated 
"  solfataric  action  "  by  Richthofen  was  caused. 

*  U.  S.  Geol.  Expl.  of  the  4Qth  Parallel,  vol.  iii.  Mining  Industry,  Washington, 
1870,  p.  87. 

f  The  Comstock  Lode,  Its  Formation  and  History,  New  York,  1879,  p.  207. 

J  "Geology  of  the  Comstock  Lode,"  etc.,  U.  S.  Geol.  Survey,  Washington,  1882, 
pp,  230,  386. 


32  THE    GENESIS    OF    ORE-DEPOSITS. 

The  chemical  constitution  of  these  intruding  waters  will  be 
considered  further  on,  after  certain  phenomena  occurring  nearer 
to  the  surface  have  received  attention. 

Related  Phenomena  Near  the  Surface. — A  sort  of  transition  to 
the  corresponding  phenomena  on  the  surface  itself  is  illustrated 
by  the  mines  at  Sulphur  Bank,  Cal.,  which  have  furnished 
some  of  the  most  important  data  contributed  by  America  to 
the  study  of  the  genesis  of  ore-deposits. 

This  is  a  once  rich,  but  now  (apparently)  practically  exhausted 
quicksilver-mine,  in  the  working  of  which  not  only  thermal 
wraters  but  gaseous  emanations  were  encountered  as  obstacles. 
At  the  time  of  my  visit  in  1876  an  open-cut  exploitation  was 
in  progress,  the  terraces  of  which  had  extended  in  some  places 
about  5  m.  (16  feet)  below  the  natural  surface.  Sulphur,  as 
well  as  quicksilver,  was  won ;  but  it  subsequently  appeared 
that  the  sulphur-deposit  was  confined  to  the  uppermost  zone, 
while  the  quicksilver  (or  cinnabar)  extended  in  considerable  pro- 
portions to  deeper  regions. 

At  that  time  I  found  sulphur  and  cinnabar  in  a  decomposed 
basalt,  partly  as  the  filling  of  irregular  fissures,  traversing  the 
rock  in  all  directions,  partly  as  impregnations  in  the  rock  itself, 
which  had  often  been  reduced  to  a  porous  mass.  The  process 
of  decomposition  proceeded  unquestionably  from  the  fissures, 
which,  moreover,  gave  forth  hot  mineral  waters  and  gases. 
The  odor  alone  was  sufficient  proof  that  the  gases  contained  H2S, 
to  the  oxidation  of  which  into  SH2O4  the  acid  reaction  of  the 
rock  and  its  moisture  was  to  be  ascribed.  The  miners  (mostly 
Chinese)  chiefly  followed  in  extraction  the  fissures  (partly  be- 
cause it  was  the  easiest  way  to  make  rapid  progress;  partly 
because  the  richest  ores  were  there  concentrated) ;  and,  as  a 
result,  large  round  blocks,  often  several  meters  in  diameter, 
were  left  standing.  These  had  a  distinct  shaly  structure,  but 
were  so  loosely  held  together  that  a  kick  would  reduce  them  to 
ruins.  In  the  interior  of  the  larger,  light-gray  blocks,  was 
often  found  a  nucleus  of  solid,  dark,  undecomposed  rock. 
(Some  of  these  nuclei  I  have  added  to  the  collection  of  the 
Przibram  Mining  Academy.) 

The  cracks  were  filled  chiefly  with  an  opaline  mass  in  which 
a  white,  opaque  ingredient  was  variously  kneaded,  as  it  were, 
with  a  gray  to  black  one,  translucent  at  the  edges.  The  speci- 


THE    GENESIS    OF    ORE-DEPOSITS.  33 

mens  taken  fell  into  irregular  pieces,  bounded  by  fissures, 
evidently  the  result  of  loss  of  volume  or  loss  of  moisture  by 
the  opaline  mass. 

The  cinnabar  formed  either  distinct  mineral  crusts  in  the 
crevices  or  impregnations  of  the  porous  neighboring  rock. 
This  was  true  of  the  sulphur  also;  only,  the  latter  appeared, 
as  a  rule,  in  crystalline  aggregates  upon  the  cinnabar  crusts — 
an  indication  of  its  later  origin.  Occasionally  the  cinnabar 
was  deposited  in  beautiful  crystals  on  the  fissure-walls,  but 
these  were  generally  so  loosely  attached  that  it  was  difficult 
to  secure  a  specimen. 

The  pyrites,  mostly  disseminated  in  the  rock,  tended  so 
strongly  to  decomposition,  evident!}7  by  reason  of  its  saturation 
with  sulphuric  acid,  that  specimens  containing  it  soon  fell  to 
pieces. 

These  observations  suffice  to  show  that  in  this  case  hot 
mineral-waters  ascend  through  fissures  containing  ore-crusts 
and  opaline  deposits ;  and  when  it  is  considered  that  the  de- 
posit of  amorphous,  hydrated  silica  is  unquestionably  the  work 
of  the  mineral  water  which  decomposed  the  rock,  and,  also, 
that  the  cinnabar  occurs  in  the  interior  of  the  opaline  mass, 
the  two  phenomena  cannot  well  be  separated,  and  it  must  be 
assumed  that  a  metallic  sulphide  has  here  been  deposited  from 
an  ascending  spring.  Fig.  10  represents  the  exposure  as 
sketched  in  my  note-book. 

Later  developments  exhibit  these  relations  still  more  clearly. 
Le  Conte  and  Becker*  found  a  shaft  50  m.  (164  feet)  from  the 
basalt,  about  92  m.  (302  feet)  deep  in  sandstone,  from  which 
drifts  had  been  run  northward  at  different  levels  under 
the  outcrops  of  the  deposit.  It  is  to  be  regretted  that  their 
reports  are  not  accompanied  with  precise  descriptions  of  the 
mine-workings.  In  the  third  level  (64  m.  =  209  feet  below 
the  surface)  the  drift  was  70  m.  (230  feet)  long,  "  cutting 
through  the  ore-body  and  reaching  only  barren  rock  on  the 

*  "  The  Phenomena  of  Metalliferous  Vein-Formation,  Now  in  Progress  at  Sul- 
phur Bank,"  by  J.  Le  Conte  and  W.  B.  Rising,  Am.  Jour,  of  Sci.,  xxv.,  p.  424. 

"On  Mineral  Veins,  Now  in  Progress  at  Steamboat  Springs,  Compared  with 
the  same  at  Sulphur  Bank,"  by  J.  Le  Conte,  Am.  Jour,  of  Sci.,  xxv  ,  p.  424. 

"Geology  of  the  Quicksilver-Deposits  of  the  Pacific  Slope,"  by  G.  F.  Becker, 
Monograph  U.  S.  Geol.  Surv.,  Washington,  1888,  p.  251. 


34  THE    GENESIS    OF    ORE-DEPOSITS. 

other  side.  The  fourth  level  has  been  pushed  31  m.  (101  feet), 
and  has  reached  the  ore-body."  From  these  data  it  is  hardly 
possible  to  form  an  idea  of  the  position  of  the  ore-body  traversed. 

The  data  given  concerning  the  interior  structure  of  the  de- 
posits are,  however,  important.  Sandstones  and  slates  are  here 
broken  up  by  fissures  in  such  a  way  as  often  to  form  a  breccia. 
Whether  the  fragments  belong  together,  and  whether  they 
present  the  relation  which  I  have  denominated  ty phonic,  is  not 
stated ;  but  it  may  be  inferred  from  the  sketch  of  an  ore-speci- 
men from  this  place  that  the  fragments  do  not  belong  together, 
and  that  their  condition  has  been  brought  about  by  more  ex- 
treme dislocations.  The  subject  is  highly  important  for  us  ;  and 
I  have  attempted  in  Fig.  11,  although  the  original  is  not  before 
rne,  to  represent  it  according  to  Le  Conte's  sketch,  so  as  to 
place  it  side  by  side  with  other  phenomena  thoroughly  familiar 
to  me. 

The  fragments  of  slate  and  sandstone  have  somewhat  rounded 
edges,  and  leave  varied  interspaces,  which  are  filled,  partly  with 
a  still  soft  or  already  indurated  paste,  containing  finely  dis- 
seminated metallic  sulphides,  partly  with  cinnabar,  for  the  most 
part  in  coherent  crusts.  A  part  of  the  space  is  usually  empty, 
exhibiting  what  I  call  a  central  druse.  Sometimes,  it  is  said, 
the  rock-fragments  are  cemented  together  with  massive  cin- 
nabar, and  kernels  of  rock  crusted  with  cinnabar  occur  fre- 
quently. 

Hot  mineral  water  and  gases  carrying  H2S  force  their  way 
through  the  interstices  of  the  deposit,  as  was  the  case  observed 
in  the  upper  zones.  The  silica  deposits  are  found  in  all  stages 
of  consolidation,  from  a  gelatinous  mass  to  chalcedony  and 
(Leconte,  op.  cit.,  p.  29)  alternate  with  layers  (crusts)  of  metallic 
sulphides  (cinnabar  and  pyrites).  Becker  examined  the  whole 
neighborhood,  and  extended  his  studies  to  similar  ore-deposits 
of  the  region.  He  does  not  consider  the  basalt  of  Sulphur 
Bank,  as  do  Gr.  Holland*  and  Le  Conte,  to  be  a  lava-stream, 
but  takes  it  to  be  an  eruptive  rock,  originating  on  the  spot, 
which  has  overflowed  a  fresh-water  formation  of  recent  age. 
The  bottom  proper  is  a  Cretaceous  sandstone.  The  ore-bearing 
character  extends  from  the  basalt  (about  16m. =52  feet  thick) 

*  "Les  Gisements  de  Mercure  de  Californie,"  Annales  des  Mines,  1878,  p.  26. 


THE    GENESIS    OF    ORE-DEPOSITS.  35 

through  the  fresh-water  layers  in  to  the  Cretaceous  sandstone. 
Concerning  its  relations  in  the  middle  layer  we  have  no  data, 
which  is  unfortunate,  since  the  effects  of  the  acid  waters  upon 
this  calcareous  material  must  have  been  considerable,  and  it  is 
not  unlikely  that  the  deposit  had  in  this  region  a  totally  differ- 
ent character.  Fresh-water  formations  adjoining  the  deposit 
have  preserved  to  a  remarkable  degree  plant-roots,  etc.,  trans- 
formed into  lime  carbonate  ;  and  it  would  be  very  instructive  to 
study  their  forms  as  metamorphosed  by  the  mineral  water. 

Concerning  the  chemical  constitution  of  the  warm  (80°  C.= 
176°  F.)  water,  I  shall  speak  further.  According  to  Becker's 
analysis  (op.  cit.,  p.  259),  it  is  extraordinarily  rich  in  chlorides, 
borax  and  sodium  carbonate.  The  gas  liberated  from  it  often 
proved  to  be  ammoniacal,  and  consisted  in  1000  parts  of  893 
parts  C02,  2  parts  H2S,  79  parts  CH4  (marsh  gas)  and  25  parts 
nitrogen. 

As  to  the  presence  of  other  metals  besides  mercury,  it  is 
worthy  of  mention  that  Dr.  Melville  found  small  amounts  of 
gold  and  copper  in  the  marcasite  accompanying  the  cinnabar, 
and  that  Gr.  Becker  found  in  the  efflorescence  from  the  mine- 
workings,  besides  the  substances  detected  in  the  mineral  water, 
traces  of  cobalt  and  nickel. 

As  will  be  seen,  this  deposit  furnishes  genetic  data,  concern- 
ing not  only  the  ores  of  quicksilver,  but  also  those  of  other 
metals.  An  ascending  mineral  spring  here  passes  from  the 
deep  into  the  shallow  region,  and  suffers,  besides  the  reduction 
of  pressure  and  temperature,  the  oxidation  of  its  H2S,  from 
which  result  a  strong  acid  and  the  deposition  of  sulphur  nearest 
the  surface. 

In  depth  no  sulphur  is  found,  but  sulphides  of  quicksilver 
and  iron,  upon  or  within  deposits  of  silica,  both  being  in  dis- 
tinct alternating  mineral  crusts.  It  cannot  be  doubted  that 
cinnabar  and  pyrites  on  the  one  hand,  and  silica,  on  the  other, 
have  been  precipitated  from  the  solution  which  still  ascends  in 
these  channels.  At  most,  it  may  be  doubted  whether  this  pre- 
cipitation is  still  going  on.  Le  Conte  adduces  in  support  of  the 
probable  continuance  of  the  process  the  occurrence  of  silica 
sometimes  gelatinous  and  soft,  as  if  recently  precipitated. 
Becker  and  Melville  tried  to  obtain  direct  evidence  of  the  pres- 
ence of  quicksilver  dissolved  in  the  ascending  mineral  water  of 

3 


36  THE    GENESIS    OF    ORE-DEPOSITS. 

to-day,  but  their  careful  investigations  failed  to  find  it.  Al- 
though the  water  contains  ingredients  in  which  quicksilver  is 
soluble,  there  is  no  quicksilver  dissolved,  and  it  must  have  been 
already  precipitated  by  some  agent — as  they  suggest,  ammonia. 

There  are  among  geologists  unbelieving  Thomases  enough, 
who  will  believe  in  the  presence  of  quicksilver  in  the  mineral 
solution  only  when  it  has  been  actually  precipitated  for  them ; 
but  there  are  those,  on  the  other  hand,  who  are  convinced  by 
the  evidence  thus  far  gathered  that  the  sulphide  deposits  of 
this  locality  proceeded  from  the  ascending  thermal  spring, 
whether  the  process  of  precipitation  is  still  going  on  or  not. 

Equally  weighty  data  are  furnished  by  Steamboat  Springs  in 
Nevada,  to  which  Laur  and  J.  A.  Phillips  first  called  attention, 
and  which  Le  Conte  and  Becker  investigated  thoroughly.*  In 
a  valley  surrounded  with  eruptive  rocks,  but  underlain  chiefly 
by  Archsean  rocks,  thermal  springs  may  be  seen  at  several 
points  emerging  from  north-and-south  fissures.  The  action  of 
these  springs  has  covered  the  ground  with  a  sinter-deposit, 
predominately  of  lime  carbonates,  about  15  m.  (49  feet)  thick. 
In  this  sinter  may  be  traced  many  fissures,  here  and  there  still 
open,  but  mostly  closed  by  the  deposit  of  silica  on  their  walls. 
According  to  a  sketch  given  by  Le  Conte,  these  very  clearly 
crustified  deposits  extend  somewhat  above  the  general  level  of 
the  surface,  forming  single  mounds  or  chains  of  mounds. 

From  some  of  them  hot  vapors  and  gases  still  issue,  chiefly 
C02  containing  H2S.  In  others,  such  emanations  have  been 
so  greatly  diminished  that  only  by  listening  can  the  liberation 
of  vapor  in  depth  be  perceived.  Some  of  the  fissures  are  com- 
pletely filled,  and  give  forth  neither  mineral  water,  steam  nor 


In  the  group,  about  200  m.  (656  feet)  wide  and  1  kilom.  (0.6 
mile)  long,  which  lies  nearest  to  the  railway-track,  these  phe- 
nomena are  most  strikingly  exhibited.  Besides  the  principal 

*  M.  Laur,  "  Sur  le  gisement  et  P  exploitation  de  1'or  en  Calif  ornie,"  Annales 
des  Mines,  1863,  iii.,  p.  423. 

J.  A.  Phillips,  Phil.  Mag.,  1871,  xlii.,  p.  401.  Also  A  Treatise  on  Ore-Deposits. 
London,  1884,  p.  70. 

J.  Le  Conte,  ' '  On  Mineral  Veins  now  in  Progress  at  Steamboat  Springs  Com- 
pared with  the  Same  at  Sulphur  Bank,"  Am.  Jour.  Sci.,  xxv.,  p.  424. 

G.  F.  Becker,  "  Geology  of  the  Quicksilver-Deposits  of  the  Pacific  Slope,"  Mono- 
graph U.  S.  Geol.  Survey,  Washington,  1888,  pp.  331. 


THE    GENESIS    OF    ORE-DEPOSITS.  37 

substances  mentioned  below  in  the  table,  Becker  found  in  this 
mineral  water  also  small  amounts  of  metallic  compounds,  as, 
for  instance,  HgS,  a  trace  of  Na2S,  1.0  gramme  per  ton  of 
Na2SbS3,  and  8.7  grammes  per  ton  of  N"a2AsS3. 

About  1J  kilom.  (1  mile)  to  the  west  is  a  group  of  similar 
fissures,  yielding  some  steam  and  C02,  but  no  mineral  water. 
In  the  mineral  crusts  of  these,  however,  several  metallic  sul- 
phides occur.  In  1863,  Laur  declared  that  he  had  seen  in 
them  distinct  traces  of  gold.  In  1878,  one  of  these  fissures 
was  opened  by  an  adit,  about  15m.  (49  feet)  under  the  surface, 
and  produced  a  vein-matter  carrying  cinnabar,  which  was 
mined  for  a  while  as  quicksilver-ore.  The  temperature  of  this 
mine  was  not  so  high  as  to  cause  serious  trouble  to  the  work- 
men. 

G.  F.  Becker  carefully  analyzed  the  filling  of  several  fissures, 
and  found,  besides  hydrated  ferric  oxide,  considerable  quanti- 
ties of  Sb,  As,  Pb,  Cu,  Hg  sulphides  and  gold  and  silver,  as 
well  as  traces  of  Zn,  Mn,  Co  and  Ni.  Since  from  1  to  3.5 
kilog.  (2.2  to  7.7  Ibs.)  of  the  vein-stuff  were  employed  for  each 
analysis,  the  results  are  specially  trustworthy,  and  I  give  the 
records  of  three  analyses  here,  expressing  them  in  grammes 

per  ton  (1  ton  =  1,000,000  grammes) : 

i.          ii.  in. 

Sulphides  of  antimony  and  arsenic,     .         23,000.0  150.0 

Ferric  oxide,        .         .         .         .         2,500.0        

Sulphide  of  mercury,  .....        1.4  2.5  1.0 

Lead, 88.0  21.0 

Copper,       .       y    ' 0.3  12.0        

Gold,  .        .        ...        .        .        .       0.9  1.0 

Silver,          .        .  '     .         .         .         .         .0.3  0.3        

(Considering  the  gold  and  silver  to  be  alloyed  in  the  above 
proportions,  we  should  have  bullion  0.750  and  0.769  fine,  which 
is  the  general  grade  of  the  so-called  "  free  gold  "  of  Transyl- 
vania.) 

The  careful  study  of  the  phenomena,  particularly  by  G.  F. 
Becker,  leaves  no  doubt  that  in  this  case  ascending  mineral 
waters  have  deposited,  besides  the  various  forms  of  silica  (from 
opal  to  crystalline  quartz),  different  metallic  sulphides,  and 
that  the  fissure-fillings  exhibit  a  very  clear  instance  of  crustifi- 
cation.  It  is,  indeed,  not  proved  that  the  process  is  now  going 
on.  But  that  is  not  the  main  point.  We  may  be  content  to 
have  the  proof  that  it  has  taken  place. 


38  THE    GENESIS    OF    ORE-DEPOSITS. 

Mineral  Springs  at  the  Surface. — When  we  isolate  a  spring 
characterized  by  high  temperature,  a  large  quantity  of  gas  or 
of  matter  in  solution,  we  notice  at  once  that  its  level  is  higher 
than  that  of  the  ground-water.  The  more  thorough  the  isola- 
tion or  walling-in,  the  more  striking  is  this  phenomenon,  so 
clearly  unlike  that  of  the  vadose  or  shallow  circulation. 

Isolation  is  usually  performed  by  digging  as  deep  as  possible, 
so  as  to  get  at  the  spring  below  the  loose  surface-material  in 
an  impermeable  rock,  and  then,  by  building  a  well-pit,  to  give 
it  freer  ascent.  But  since  the  circulation  of  the  ground-water 
in  the  loose  surface  is  very  lively,  the  necessary  depression 
of  the  water-level  in  such  an  excavation  involves  the  lifting 
of  large  quantities  of  water.  Moreover,  the  escape  of  the  gas 
from  the  mineral  spring  often  hinders  the  operation ;  so  that 
there  is,  as  a  rule,  little  opportunity  for  thorough  investigation. 
Cases  in  which  accurate  observations  have  been  properly  re- 
corded for  preservation  are  very  rare. 

The  first  good  fissure  encountered  in  the  bed-rock  is  deemed 
to  be  the  channel  of  the  mineral  spring,  and  the  well  is  built 
over  it.  Complete  isolation  from  the  ground-water  is  proba- 
bly seldom  practicable.  Nevertheless,  the  mineral  spring, 
being  under  higher  pressure  than  the  ground-water,  will  tend 
to  exclude  it  from  the  well.  The  imperfection  of  the  isolation 
is  shown,  however,  when  we  try  for  any  reason  to  pump  out 
the  well.  To  lower  the  water-level,  say  1  m.  (3.28  feet),  we 
have  to  raise  many  times  the  amount  of  water  which  the  spring 
itself  would  normally  furnish  (even  taking  into  account  the  de- 
creased pressure,  which  affects  the  flow  in  the  proportion  of  the 
square  root  of  the  head).  The  excess,  generally  surprisingly 
great,  comes  from  the  ground-water  which  finds  its  way  into 
the  well. 

If  we  allow  the  mineral  water  to  ascend  again  quietly  in  the 
well,  the  level  rises  at  first  rapidly,  then  slowly,  and  finally 
remains  (in  the  absence  of  change  in  the  height  of  the  ground- 
water  and  in  the  barometric  pressure)  stationary  at  a  certain 
height  above  the  ground- water  level.  This  difference  of  height 
represents  the  ascensional  force  of  the  mineral  spring. 

If  the  spring  makes  a  deposit  at  its  mouth  (mostly  of  lime 
carbonate,  hydrated  ferric  oxide,  and  silica)  it  may  thus  build 
a  conduit,  extending  above  the  ground-water  level  and  the  sur- 


THE    GENESIS    OF    ORE-DEPOSITS.  39 

face  to  the  height  represented  by  its  ascensional  force.  Thus, 
we  find  conical  mounds  from  the  top  of  which  mineral  springs 
flow.  This  phenomenon  is  shown  in  the  highest  degree  by 
geysers,  i.e.,  thermal  springs  in  which  paroxysmal  developments 
of  steam  and  gas  occur,  often  forcing  the  water  to  notable 
heights.  Some  of  the  magnificent  geysers  of  the  Yellowstone 
National  Park  have  built  chimney-like  conduits  of  considerable 
size.  Their  structure  has  much  similarity  to  that  of  stalac- 
tites ;  indeed,  we  may  recognize  generally,  in  the  various  de- 
posits of  ascending  mineral  springs  (in  other  words,  in  the 
products  of  the  deep  circulation),  many  analogies  with  the 
vadose  circulation.  This  circumstance  indicates  a  relation  be- 
tween the  phenomena  of  the  two  regions  which  is  often  entirely 
ignored  or  even  denied. 

While,  for  instance,  the  geysers  have  a  temperature  above 
boiling-point,  some  mineral  springs  rise  but  little  above  the 
mean  local  temperature  of  the  surface  or  of  the  ground-water. 
This  may  be  especially  observed  in  the  acid  springs ;  yet,  these 
are  also  ascending  springs,  and  must  have  been  formed  in  the 
deep  region. 

Within  the  vadose  region  we  have,  sometimes,  ascending 
waters,  which  are,  however,  mostly  to  be  explained  by  hydro- 
static pressure.  But,  within  the  deep  region,  hydrostatic  pres- 
sure can  play  no  part ;  and  here  it  is  the  higher  temperature 
and  the  presence  of  gas  which  cause  the  ascension  of  mineral 
springs.  The  extreme  instances  of  this  kind,  such  as  geysers, 
steaming  springs,  mud- volcanoes, petroleum  springs,  etc.,  nobody 
will  undertake  to  explain  by  hydrostatic  pressure,  and  more 
moderate  results  of  the  same  factors  can  scarcely,  with  con- 
sistency, be  so  explained. 

It  is  a  striking  circumstance  that  ascending  springs  occur 
chiefly  in  the  neighborhood  of  the  later  eruptive  rocks,  such 
as  trachyte,  basalt,  etc.  This  is  emphatically  the  case  through- 
out the  zone  which  crosses  Europe  from  west  to  east,  in  France, 
Germany,  Bohemia,  Hungary,  and  Transylvania.  Here  the 
warm  springs  and  the  acid  springs  occur  thickly,  while  north 
and  south  of  this  zone  they  are  only  sporadic.  Their  connec- 
tion in  the  zone  with  the  eruptive  rocks  is  evident,  and  they 
are  often  considered  as  the  last  echoes  of  the  processes  of  erup- 
tion. The  sporadic  springs,  in  places  where  eruptive  rocks 


40 


THE    GENESIS    OF    ORE-DEPOSITS. 


play  no  part,  must  have  come  through  deep  fissures  of  dislo- 
cation. For  example,  the  line  of  the  fault  along  which  the 
Alps  sank  below  the  Tertiary  basin  of  Vienna  is  marked  by  a 
complete  series  of  thermal  springs. 

This  circumstance  has  another  and  far-reaching  significance. 
For  ore-deposits  are  similarly  distributed.  They  are  most 
numerous  and  most  closely  grouped  in  the  neighborhood  of 
eruptive  rocks,  especially  extended  zones  of  eruptive  rocks,  as 
in  the  American  West,  and  in  Hungary  and  Transylvania, 
while  among  other  rocks  they  are  fewer  and  more  scattered. 

Chemical  Constitution  of  Mineral  Waters. — Ascending  mineral 
springs  have  widely  varying  composition ;  some,  like  the 
"  aerotherms,"  representing  strictly  only  warmed  ground-water, 
while  others  are  strongly  mineralized,  and  carry  some  sub- 
stances almost  to  saturation.  The  material  bearing  on  this  sub- 
ject is  too  voluminous  and  heterogeneous  to  be  fully  cited  and 
discussed  here.  I  must  be  content  with  the  exhibit  of  a  few 
analyses,  specially  interesting  for  the  present  purpose. 

The  following  is  a  list  of  the  localities,  etc.,  represented  in 
the  table  below : 

Waters  Encountered  in  Mines. 


No. 


Locality. 


Temperature. 


1  Gottesgeschick  mine,  Schwarzenberg,          .     11.       51.8 

2  Einigkeits  shaft,  Joachimsthal,  .         .         .28.7    83.7 

3  The  "Sprudel,"  in  Colliery  at  Briix,  Bohemia, 

4  Comstock,  Savage,  600-foot  level,       .         .     28.  ?    82.4 

5  Comstock,  Gould  and  Curry,  1700-foot  level,  48.  ?  118.4 

6  Comstock,  Gould  and  Curry,  1800-foot  level,  50.  ?  122. 

7  Comstock,  Hale  and  Norcross,    .         .  70.  ?  158. 

8  Comstock,  Ophir,        .        ,         .        .         .     21.1     70. 


No. 


Water  in  Ore-bearing  Fissures. 

Locality.  Temperature. 


9  Sulphur  Bank,  Herman  shaft, 

10  Sulphur  Bank,  Parrot  shaft, 

11  Steamboat  Springs, 


70.  ?  158. 
70.  158. 
75.  167. 


Authority. 

K.  Kichter. 

J.  Seifert. 

J.  Gintl. 

S.  W.  Johnson. 

S.  W.  Johnson. 

S.  W.  Johnson. 

S.  W.  Johnson. 

Attwood. 


Authority. 

G.  F.  Becker. 
G.  F.  Becker. 
G.  F.  Becker. 


No. 


Some  Bohemian  Thermal  Springs. 

Locality.  Temperature. 


12  Sprudel,  Carlsbad, 

13  Kreuzbrunn,  Marienbad,    . 

14  Wiesenquelle,  Franzensbad, 

15  Urquelle,  Teplitz, 


64.  147.2 

12.  53.6 

13.  55.4 
50.  122. 


THE    GENESIS    OF    ORE-DEPOSITS.  41 

Weak  and  Strong  Mineral  Springs. 

No.                     Locality.  Authority. 

16  Ottoquelle,  Giessh libel,          .....  Dr.  Novak  Kratschmann. 

17  Josephsquelle,  Bilin  (1875),           ....  Dr.  Euppert. 

18  Puits  de  1'  Enclos  des  Celestins,  Vichy,         .         .  Bunsen. 

19  Kippoldsau,  Josephsquelle  (1875),        .         .        .  Bunsen. 

20  Kippoldsau,  Wenzelquelle  (1875),         .         .         .  Bunsen. 

21  Kippoldsau,  Leopoldquelle  (1875),        .         .         .  Bunsen. 

22  Kissingen,  Pandurquelle  (1856),            .         .         .  Liebig. 

23  Kissingen,  Rakoczyquelle  (1856),          .         ,         .  Liebig. 

24  Yellowstone,  Cleopatra,  Mammoth  Hot  Springs  (1888),  \  F.  H.  Gooch. 

25  Yellowstone,  Grand  Geyser,           .         .         .         .  /      T.  E.  Whitefield. 

It  is  well  known  that  analysts  in  combining  their  results  do 
not  follow  the  same  rule.  One  supposes  a  certain  acid  to  be 
united  with  an  alkali ;  another  gives  the  same  acid  to  an  earthy 
base,  etc.  What  interests  us  in  the  comparison  afforded  by  the 
table  is  the  substances  occurring  in  large  proportions,  the  car- 
bonates and  sulphates  of  the  alkalies  and  alkaline  earths ;  the 
chlorides,  the  silica,  and  the  quantity  of  organic  matter  (if  it 
were  determined  by  a  uniform  procedure). 

I  deem  it  most  convenient  to  take  1  ton  of  1000  kilogrammes 
(representing,  for  waters  not  too  rich  in  mineral,  the  weight  of 
1  cubic  meter),  and  to  express  the  weights  of  the  salts  in 
grammes,  to  avoid  decimals.  In  order  to  show  the  relations 
of  the  salts,  one  to  another,  it  is  well  also  to  represent  them  on 
the  basis  of  1000  parts  of  the  solid  matter. 

For  the  Comstock  waters,  the  rationally-stated  analysis  of  S. 
"W".  Johnson,  from  the  600-foot  level  of  the  Savage  mine  (C. 
King,  op.  cit.,  p.  87),  served  me  as  a  guide,  according  to  which 
I  have  recalculated  the  figures  (Church,  op.  cit.9  p.  204)  for 
other  mines  and  levels. 

These  analyses  show  the  irruptive  waters  on  the  Comstock 
to  be  poor  in  dissolved  substances.  According  to  the  deter- 
mination of  solid  residuum  by  E.  S.  Bristol  (C.  King,  1.  c.,  p. 
88),  this  would  not  be  the  case.  He  finds  the  mine-water  of 
the  500-foot  level  to  contain  in  the  Savage  north  drift  2660 
grammes,  and  in  the  Yellow  Jacket  west  drift  as  much  as  3271 
grammes  of  solid  material  in  one  ton  (1000  kilos).  But  it  is 
a  question  whether  these  figures  do  not  refer  to  ordinary  mine- 
waters,  as  the  term  "  west  drift "  seems  to  indicate. 

The  predominance  of  sulphates  over  carbonates  is  nothing 
unusual ;  but  the  decided  predominance  of  lime,  sulphate  or 


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THE    GENESIS    OF    ORE-DEPOSITS.  43 

gypsum  in  the  Comstock  waters  is  unique.  This  relation  would 
still  remain  if  we  should  reckon  a  part  of  the  sulphuric  acid 
as  combined  with  the  alkalies.  The  two  most  trustworthy 
analyses  of  Attwood  and  Johnson  give  222  and  535  grammes 
of  gypsum  per  ton  of  water,  and  492  and  700  grammes  per 
ton  of  dry  residuum.  Apart  from  their  gypsum,  the  Comstock 
irruptive  waters  may  be  classed  among  the  weak  or  acrother- 
mal  springs,  like  those  of  Teplitz  in  Bohemia. 

The  Sulphur  Bank  and  Steamboat  Springs  waters  are  dis- 
tinguished from  all  others  in  the  table  by  a  considerable  pro- 
portion of  sodium  biborate,  and  resemble  unmistakably  certain 
Suffioni  and  Lagoni  waters  of  Middle  Italy.  Their  degree  of 
impregnation  and  their  large  proportion  of  chlorides  bring 
them  near  the  waters  of  Carlsbad  and  Franzensbad,  Bohemia. 
The  proportion  of  sodium  chloride  is  not  surprising  in  the 
American  West,  in  the  neighborhood  of  undrained  and  there- 
fore salt  regions,  but  it  is  surprising  in  Bohemia,  a  country 
notoriously  free  from  salt,  in  which  no  rock  is  known  to  con- 
tain these  highly  soluble  substances.  We  must  assume  that 
they  exist  in  the  deeper  region,  in  forms  not  yet  decomposed, 
such  as  sodalite  (3^N"a2Al2Si208  -f-2NaCl)  which  must  be  chem- 
ically decomposed  before  its  Nad  can  be  dissolved.  The 
presence  of  quantities  of  salt  smaller  than  those  here  under 
consideration  can  be  attributed  (as  I  at  one  time  attempted  to 
show)*  to  atmospheric  precipitation.  A.  Bobierre  foundf  by 
careful  and  continuous  analysis  of  the  rain-water  falling  in 
Nancy  throughout  the  year  1863,  14  grammes  of  salt  per  ton 
or  cubic  meter;  and  G.  ZoppeJ  has  argued  that  the  sometimes 
considerable  contents  of  sodium  chloride  in  the  springs  of  the 
Iglesiente  district,  in  the  island  of  Sardinia,  can  only  be  ex- 
plained by  the  transportation  of  salt  from  the  sea  by  wind.  (A 
stormy  cloud-burst,  March  7,  1886,  showed  as  much  as  387 
grammes  per  ton  or  cubic  meter.)  The  salt  of  the  atmospheric 
precipitation  is  concentrated  by  evaporation.  In  Bohemia,  for 
instance,  only  one-fourth  of  the  rainfall  escapes  into  the  Elbe ; 

*  "  Zur  Genesis  der  Salzablagerungen,  besonders  jener  im  pordamerikanischen. 
Westen,"  k.k.  Akad.  d.  Wissensch.,  Wein,  1877. 

f  Compt.  rend.,  Iviii.,  p.  755.     Bullet.  Soc.  Chim.,  liv.,  p.  467. 

J  "  Descrizione  geologico-mineraria  dell'  Iglesiente/'-Memon'e  descritt.  delta  Carta 
geol.  d' Italia,  iv.,  Roma,  1888,  p.  119. 


44  THE    GENESIS    OF    ORE-DEPOSITS. 

in  more  southern  regions  the  whole  evaporates.  The  descending 
ground-water  is  still  further  concentrated  ;  so  that  in  this  way 
the  salt  normally  found  in  the  ascending  waters  may  be 
accounted  for. 

But  while  the  water  of  Steamboat  Springs  is  rich  in  sodium 
chloride,  the  Comstock  mine-water  is  poor,  notwithstanding  the 
comparatively  near  neighborhood  of  the  two  places.  Both 
adjoin  eruptive  rocks,  especially  basaltic  outflows ;  but  the 
Steamboat  Springs  break  out  of  crystalline  rocks.  May  not 
the  ascending  waters  have  derived  their  abundant  sodium 
chloride  from  minerals,  like  sodalite,  which  contain  it  chemic- 
ally bound  ? 

Hydrogen  sulphide  plays  an  important  part  in  the  ascending 
waters.  Its  presence  seems  to  be  the  cause  of  a  greater 
abundance  of  dissolved  substances.  It  is  attributed  to  the  de- 
composition of  sulphates  through  the  organic  matter,  traces  of 
which  are  found  in  most  of  the  ascending  waters.  By  re- 
oxidation,  it  produces  the  sulphuric  acid  which  transforms  car- 
bonates into  sulphates.  It  is  remarkable  that  in  many  mineral 
springs  H2S  appears  periodically  in  surprising  excess,  and  often 
disappears  again,  almost  without  leaving  a  trace.  It  is  probable 
that  an  alternation  of  the  processes  of  oxidation  and  reduction 
wrould  produce  this  phenomenon. 

The  most  important  geological  factor  in  ascending  waters  is 
undoubtedly  carbonic  acid;  for  it  is  chiefly  this  compound 
which  in  the  deep  region,  under  high  temperature  and  pressure, 
develops  a  greater  solvent  power  for  most  of  the  elements  of 
the  rocks.  The  alkalies,  earths  and  silica  of  our  mineral 
springs  have  certainly  been  dissolved  from  the  rocks  by  car- 
bonic acid,  and  the  carbonates  thus  formed  usually  predomi- 
nate over  the  associated  sulphates.  The  analyses  do  not  give 
us  the  conditions  in  which  they  exist,  because  the  statements 
of  results  depend  largely  upon  the  individual  views  of  the 
analysts. 

The  general  exhibit  sketched  above  shows  that  in  the  Com- 
stock waters  the  sulphates  exceed  the  carbonates,  and  that  the 
chemists  have  been  led  to  connect  the  sulphuric  acid  prefera- 
bly with  the  earths.  They  have  simply  found  an  excess  of 
sulphuric  over  carbonic  acid,  as  is  the  case  also  in  the  strong 
thermal  springs  of  Bohemia.  The  relation  between  the  two 


THE    GENESIS    OF    ORE-DEPOSITS.  45 

analyses  of  Sulphur  Bank  water  is  remarkable ;  one  showing 
the  sulphates,  and  the  other  carbonates,  to  be  predominant. 
Apparently  one  sample  was  taken  from  water  which  had  been 
for  a  considerable  period  in  contact  with  the  atmosphere,  so 
that  the  liberated  H2S  gas,  oxidizing  to  H2S04,  expelled  the 
C02  from  a  part  of  the  carbonates.  The  three  irruptive  ther- 
mal waters,  Nos.  1,  2  and  3  in  the  table,  are  acid,  and  also  con- 
tain a  notable  quantity  of  free  C02  in  solution — which,  indeed, 
determines  their  acid  character.  I  have  added  for  comparison 
Nos.  16  and  17,  two  favorite  Bohemian  acid  springs.  No.  18 
is  the  famous  Vichy  spring  in  France;  No.  16  is  a  weak  water, 
esteemed  for  table-use;  and  No.  17  is  the  celebrated  stronger 
water  of  Bilin.  A  few  years  ago,  the  quantity  of  the  latter 
spring  had  seriously  fallen  off';  and  there  is  reason  to  surmise 
that  a  part  of  its  water  had  found  a  way  into  the  collieries  of 
Briix,  where  similar  acid  springs  appear  at  several  points. 
Fortunately  for  Bilin,  an  increased  supply  was  obtained  there 
by  means  of  an  adit  and  bore-hole.  It  is  known  that  distilled 
water  at  normal  barometric  pressure  and  ordinary  indoor  tem- 
perature may  contain  in  absorption  an  equal  volume  of  car- 
bonic acid,  and  that  mineral  water  under  the  same  conditions 
has  a  somewhat  higher  absorption-coefficient.  The  free  C02, 
not  held  in  bicarbonates,  is  mostly  given  by  analysts  in  terms 
of  weight.  These,  by  the  employment  of  the  well-known  vol- 
ume of  one  gramme  of  C02,  could  be  easily  transferred  into 
terms  of  volume,  a  more  practical  form  for  all  cases,  which  is 
unfortunately  not  yet  generally  used. 

Since  in  the  deep  regions  the  absorption-capacity  of  water  for 
C02  is  diminished  by  increased  temperature,  but,  on  the  other 
hand,  increased  in  much  greater  proportion  by  increase  of 
pressure,  a  portion  of  the  gas  absorbed  in  depth  is  liberated  in 
the  higher  region  and  contributes  energy  to  the  ascending  cur- 
rent. 

Thus  far  the  substances  present  in  mineral  waters  in  the 
largest  proportions  have  been  chiefly  considered.  We  must 
now  study  also  those  which  occur  in  minute  proportions,  since 
these  concern  most  nearly  the  question  with  which  we  are 
dealing. 

Minute  Metallic  Admixtures  in  Mineral  Waters. — Ordinary  an- 
alyses show  the  presence  of  some  metals,  especially  iron  and  man- 


46  THE    GENESIS    OF    ORE-DEPOSITS. 

ganese,  which  occur  as  easily  oxidizable  protoxides,  giving  rise 
to  the  precipitation  of  hydrated  peroxides.  Lime  carbonate  in 
solution  as  bicarbonate,  is  simultaneously  precipitated  by  evapor- 
ation and  the  loss  of  C02 ;  and  silica  is  likewise  thrown  down  un- 
der certain  conditions.  Such  precipitates  are  called,  according  to 
their  predominent  ingredients,  ocher,  sinter,  tufa,  travertine,  etc. 
Minute  metallic  admixtures  are  found : 

1.  Dissolved  in  the  mineral  water  itself. 

2.  In  the  ochers  or  sinters  deposited  at  the  mouths  of  springs, 
where  they  are  concentrated  in   observable  quantity,  having 
been,  without  doubt,  originally  held  in  solution  by  the  springs. 

3.  Moreover,  there  are  found,  in  some  places,  at  the  mouths 
of  springs,  substances  which  were  not  originally  in  the   solu- 
tion, but  have  been  subsequently  dissolved  and  ultimately  pre- 
cipitated  by  the    action    of  the  mineral  water  upon  various 
foreign  bodies  attacked  by  it. 

The  proportions  of  metallic  ingredients  found  in  ordinary 
spring-analyses  were  at  first  generally  regarded  with  doubt, 
unless  a  chemist  of  the  rank  of  Berzelius  vouched  for  them. 
Fresenius  and  others  admitted  that  such  ingredients  might  be 
taken  up  from  metallic  conduits.  But  at  last  they  were  proved 
to  exist  in  springs,  excluding  this  hypothesis.  Of  course, 
"  traces  "  are  worthy  of  less  confidence  than  ponderable  quan- 
tities. According  to  Dr.  Loschner,*  Gottl  found  in  the  GTeiss- 
hubl  waters  "  traces  "  of  copper,  and  even  of  gold.  Of  the 
fifty-nine  chemical  elements  recognized  in  1847,  twenty-four 
were  known  to  Elie  de  Beaumontf  as  occurring  in  mineral 
springs.  Of  these  only  six  (Ur,  Mn,  Fe,  Bi,  Sb,  As)  were 
metals.  Gr.  Bischof  f  doubled  this  list,  and  the  knowledge  of 
the  subject  has  been  greatly  increased  since  by  Liebig,  Will, 
Fresenius,  Rammelsberg,  Wackenroder,  Thenard  and  Cheva- 
lier. It  is  chiefly  from  the  deposits  of  springs  that  we  learn 
of  the  minute  metallic  substances  once  dissolved  in  them.  The 
oxides  of  Cu,  Sn,  Co,  Zn,  Sb,  !N"i,  etc.,  were  precipitated  to- 
gether with  the  oxide  of  iron.  Ochers  are  especially  rich  in 
arsenic.  Tin  is  often  found  in  -the  thermal  deposits  of  Wies- 
baden, Soden,  Homburg,  Rippoldsau,  Alexisbad,  Driburg, 
Bruckenau,  Kissingen,  etc. 

*  Badeschrift  iiber  Giesshubl,  3  Aufl.  Prag.,  1855. 

f  Bulletin  de  la  Soc.  Geol.  de  France,  2  Ser.,  iv.,  p.  1249,  etc. 

J  Lehrb.  d.  Chem.  Geologic,  Aufl.,  i.,  p.  2078. 


THE    GENESIS    OF    ORE-DEPOSITS. 


Lead  occurs  in  the  springs  of  Rippoldsau  (according  to  "Will, 
1.6  to  3.7  milligrammes  per  ton),  Kissingen  (10  to  13  mg.  per 
ton),  Alexisbad,  Ems,  Homburg,  Carlsbad  (in  the  Schlossbrunn, 
according  to  Gottl),  Pyrmont,  etc.*  Copper  has  long  been 
known  to  exist  in  acid  mine-waters  (e.g.,  the  cement-waters  of 
Schmollnitz,  Herrengrund  in  Hungary,  etc.),  and  is  found  also 
in  ascending  waters  at  Carlsbad  (authority,  Gottl),  Aachen 
(Liebig),  Bagneres  de  Luchon  (Filhol),  Bourbonne  (Tomsier), 
Luxueil  (Braconnot,  Henry),  "Wiesbaden  (Fresenius),  Briicke- 
nau  (Keller),  Eippoldsau  (Will),  and  in  many  other  chalybeate 
waters. f  Arsenic  is,  of  course,  often  found  in  mineral  waters. 
I  will  mention  only  the  Magdalena  spring  of  Mont-Dore  (45  to 
55  grammes  per  ton,  says  Thenard),  St.  Hectaire  (6  to  8  per 
ton),  Royat  (35  g.  per  ton),  and  Bourbole  (815  g.  per  ton).  G-. 
Bischof  J  gives  as  follows  the  maxima  found  in  mineral  springs 
up  to  1854  : 

Milligrammes  per  Ton. 

Of  Water.  Of  Ocher. 

Arsenious  acid,       .         .        ...         .1.5  38.460 

Antimony  oxide,    .      ..«    ..    •     ..;;.'  •       0.1  

Zinc  oxide  (sulphate),  .'.       V^    .         .     13.3  

Lead  oxide, '      .       0.1  1.900 

Copper  oxide,     xi'  -"»'       ....       6.4  l.OCO 

Tin  oxide, 0.1  .50 

I  add,  as  illustration,  the  contents  of  the  mineral  waters  of 
two  important  localities,  as  calculated  from  the  contents  of  the 
ocher.  The  chief  constituents  of  these  waters  are  given  in  the 
table  on  page  42.  The  first  three  springs  are  at  Bippoldsau. 


LOCALITY  : 

Rippoldsau  (ace.  to  WILL.)     Kissingen  (ace.  to  KELLER.) 

Springs  : 

Josef. 

Wenzel. 

Leopold. 

Pandur. 

Rakoczy. 

Constituents. 

Milligrammes  per  ton. 

Protoxide  of  tin  

25 

16 
104 
600 

17 
10 
69 
400 

38 
24 
156 
900 

134 
107 
128 
1120 

166 
134 
150 

800 

Antimony  oxide  

Copper  oxide 

Arsenious  acid 

In  discussing  Steamboat  Springs  I  have  already  mentioned 

*  Dr.  B.  M.  Lersch,  Hydrochemie,  i.,  Berlin,  1879,  p.  342. 
f  Ibid.,  p.  438. 

,J  Dr.  H.   Ludwig's  Die  natiirlichen  Wasser,  Erlangen,  1862,  p.  96.     Compare 
J.  Koth's  Attgemeine  Chem.  Geologic,  Berlin,  1879,  p.  564,  etc. 


48  THE    GENESIS    OF    ORE-DEPOSITS. 

the  metals  found  by  GL  F.  Becker,  among  which  are  Hg,  Au, 
and  Ag. 

I  would  only,  in  addition,  call  attention  to  the  variations  in 
the  deposit  of  one  and  the  same  spring,  for  which  purpose  I 
select  the  Puits  de  1'  Enclos  des  Celestins,  at  Vichy,*  of  which 
an  analysis  is  given  in  the  table  on  page  42.  This  contains  in 
1000  parts : 

Residuum  obtained  by 

evaporating  the  Ocherous       Calcareous 

mineral  water.  deposit.  deposit. 

Alkaline,  carbonates,  .         .  735                        

Earthy  carbonates,  .  ...  129  169  980 

Ferrous  carbonates,  .  .         .  3                         

Manganous  carbonates,  .         4 

Iron  oxide,       .         .  .         .     474  1.0 

Alkaline  sulphates,  .  '.         .  42                        

Chlorides,          .'       .  .         .  72                        

Silica,                ....  8  10              

Arsenic  acid,    .         .  .         .  0.4  70              

Other  constituents,   .  .         .  10.6  277  6 

1000.0  1000  1000 

Alterations  Produced  by  Mineral  Springs. — Daubree,  in  the 
chapters  devoted  to  this  subject,  distinguishes  the  action  of 
mineral  waters  upon  the  rock  they  traverse,  and  their  action 
upon  artificial  substances  which  have  found  their  way  into  the 
mineral  water,  f 

a.  Under  the  first  head  he  cites  alunite,  kaoline  and  serpen- 
tine as  a  result  of  mineral  springs  in  general.  I  would. call 
attention,  however,  to  the  circumstance,  not  yet  sufficiently  ap- 
preciated, that  the  rocks  in  the  neighborhood  of  a  mineral 
spring  often  have  a  very  different  appearance  from  those  at  a 
distance.  In  the  case  of  springs  carrying  sulphuretted  hydro- 
gen, this  is  self-explanatory.  Sulphur  Bank  represents  the 
phenomenon  in  a  striking  way  as  regards  basalt.  Granite  is 
often  decomposed  in  the  neighborhood  of  springs, — as  in  the 
Carlsbad  region,  where  some  acid  springs,  like  that  of  Giess- 
hiibl,  emerging  on  the  contact  between  granite  and  the  over- 
lying Tertiary  rocks,  have  transformed  the  granite  into  kaoline. 
I  have  observed  similar  decomposition  at  the  springs  of  Johan- 
nisbad,  in  Bohemia,  and  at  many  other  places.  It  is  to  be  re- 

*  Dr.  H.  Ludwig's  Die  naturlichen  Wasser,  Erlangen,  1862,  p.  199. 
t  Les  eaux  souterraines  a  /'  epoque  actuelle,  ii.,  p.  67,  and  Les  eaux  souterraines  aux 
epoques  anciennes,  p.  178. 


THE    GENESIS    OF    ORE-DEPOSITS.  49 

gretted  that  these  phenomena  havre  been  seldom  studied,  as 
yet,  from  a  chemical  standpoint. 

Daubree  has  pointed  out  the  effect  of  mineral  water  upon 
various  rocks  and  artificial  building-materials  in  the  masonry 
shafts  of  the  springs  at  Plombieres  and  Bourbonne-les-Bains;* 
for  instance,  the  zeolites  (chabazite,  harmotome,  christianite, 
mesotype,  apophyllite)  formed  in  the  Roman  beton ;  the  hydrous 
silicates  (plombierite,  chalcedony,  hyalite)  in  the  Roman  bricks 
at  Plombieres  ;  recent  formations  of  calcite  and  aragonite,  and 
also  the  funnel-shaped  cavities  eaten  out  of  the  dressed  lime- 
stone of  the  masonry.  The  latter  are  specially  interesting  as 
having  been  excavated  from  below  upwards, — that  is,  in  the 
direction  of  the  ascending  spring.  Fig.  9  illustrates  this  action 
upon  such  a  building  stone. 

An  analagous,  and,  for  our  purpose,  still  more  important  ob- 
servation, was  made  in  1845,  at  Burtscheid,  near  Aachen,  by 
J.  Noggerath.  A  terrace  was  constructed  at  that  time  in  the 
neighborhood  of  the  hot  spring,  as  the  site  for  a  house.  Blast- 
ing in  the  Devonian  limestone  exposed  several  vertical  channels 
of  nearly  circular  section  and  20  to  90  centimeters  (8  to  35 
inches)  diameter,  some  of  which  contained  thermal  water  and 
emitted  steam.  They  had  been  partly  choked  by  rock-debris, 
but  one  of  them  showed  a  depth  of  about  4  meters  (13  feet). 
Immediately  around  these  tubes  the  elsewhere  solid  limestone 
had  been  altered  for  a  distance  of  15  centimeters  (6  inches)  to 
a  gray,  earthy  mass,  almost  plastic  when  damp,  and  separable 
in  thin  scales.  In  places,  this  earthy  mass  had  fallen  away, 
and  on  the  sides  of  the  enlargements  of  the  tube  thus  formed, 
crusts  of  white  lime-sinter' had  been  deposited. f  Noggerath 
does  not  doubt  in  the  least  that  the  mineral  water  emerged  5 
to  6  meters  (16  to  20  feet)  above  the  present  exit,  and  eroded 
the  channel  for  itself.  He  believes  even  that  the  channels  of 
all  the  mineral  springs  of  Burtscheid  and  Aachen,  which  came 
from  the  limestone,  have  a  similar  shape. 

He  calls  attention  to  the  fact,  observed  by  him  and  his  friend 
G.  Bischof,  that  the  slabs  of  black  marble  covering  the  curb- 

*  Experimental  Geology,  p.  82. 

f  J.  Noggerath, "  Ueber  die  sogenannten  natiirlichen  Schachte  oder  geologischen 
Orgeln  in  verschiedenen  Kalksteinbild ungen. ' '  Karsten'  s  Archiv.  fur  Min. ,  Geogn. ,' 
u.  Bergbau,  1845,  p.  513. 


50  THE    GENESIS    OF    ORE-DEPOSITS. 

ing  of  the  Kaiserquelle,  near  Aachen,  and  the  Schwerdbad,  at 
Burtscheid,  had  been  transformed  by  the  constant  action  of 
the  steam  upon  their  inner  surfaces  into  a  doughy  mass,  which 
could  be  easily  scratched  away  with  the  finger-nail. 

Besides  this  evident  action  of  thermal  springs  upon  lime- 
stone, we  may  conclude  from  the  foregoing  that  such  waters, 
tending  to  an  upward  movement,  may  actually  eat  their  way 
through  limestone  to  the  surface,  or  to  rocks  offering  commu- 
nication with  the  surface.  This  circumstance  was  not  known 
to  me  when  I  published  my  monograph  on  the  Rezbanya 
deposits,*  in  which  I  attributed  to  ground-water  the  erosion  of 
the  channels  in  the  limestone  which  are  filled  with  ore,  instead 
of  allowing  them  to  have  been  formed  by  the  ascending  min- 
eral waters. 

The  treatise  of  lN"oggerath  above  cited  contains  also  observa- 
tions upon  the  analogy  between  the  thermal-water  channels  of 
Burtscheid,  the  so-called  "  geological  organ-pipes "  (les  orgues 
geologiques)  in  the  chalk-deposits  of  Maestrich,  and  the  "  natural 
shafts  "  (puits  naturels]  in  the  Eocene  limestone  of  the  vicinity 
of  Paris.  The  latter,  however,  have  shown  neither  mineral 
water  nor  any  traces  of  its  former  presence,  and  are  of  little 
interest  for  us.  Recent  investigations  of  both  the  phenomena 
referred  to  are  unfortunately  not  now  at  hand. 

b.  Regarding  the  effects  of  mineral  waters  upon  artificial 
products  immersed  in  them,  we  are  indebted  to  Daubree  for  the 
preservation  of  the  numerous  important  observations  in  the 
masonry  pits  of  the  springs  of  Plombieres  and  Bourbonne-les- 
Bains.f 

The  springs  of  Plombieres  occur  in  the  neighborhood  of  ore- 
bearing  quartz-veins,  and  furnish  at  68°  C.  (154°  F.)  a  water  rich 
in  carbonic  acid  but  poor  in  solid  constituents,  the  residuum 
after  evaporation  being  400  grammes  per  ton  (0.04  per  cent.). 
Those  of  Bourbonne-les-Bains,  on  the  other  hand,  have  a  temper- 
ature of  58°  C.  (136°  F.),  and  are  rich  in  mineral  matter,  the  re- 
siduum being  7000  to  8000  grammes  per  ton  (0.7  to  0.8  per  cent), 

*  Geol.  mont.  Studie  der  Erzlagerstatten  von  Eezbanya  in  S.  0.  Ungarn.,  Budapest, 
1874,  p.  179. 

f  "  Formation  contemporaine  de  diverses  especes  minerals  cristallise's  dans  la 
source  thermale  de  Bourbonne-les  Bains."  Annalesdes  Mines,  6  series,  1875,  viii., 
p.  439.  Also,  the  German  edition  of  Daubree's  Etudes  synthetiques,  1880,  p.  57. 


THE    GENESIS    OF    ORE-DEPOSITS.  51 

chiefly  sodium  chloride  (5800  grammes).  They  flow  from  the 
variegated  marls  of  the  upper  Trias,  underlying  the  Muschel- 
kalk,  in  the  vicinity  of  large  fault-fissures.  Carbonic  acid  ap- 
pears to  be  present  in  traces  only,  and  the  same  is  true  of 
hydrogen  sulphide,  which  is  detected  by  its  odor,  and  has  given 
rise  also  to  small  deposits  of  sulphur. 

In  1874,  with  the  aid  of  powerful  pumps,  the  abundant  cur- 
rent of  the  spring  was  successfully  overcome,  and  the  founda- 
tion of  the  old  Roman  curbing  was  made  accessible.  The 
mineral  water  rises  from  horizontal  clay  beds  through  a  funnel 
filled  with  sand,  which  scarcely  represents  the  original  channel. 
At  the  bottom  of  the  masonry  lining  a  clayey  slime  was  en- 
countered, in  which,  besides  thousands  of  hazel-nuts,  acorns 
and  fruit-seeds,  many  Gothic  and  Roman  coins  were  found, 
with  numerous  other  objects,  such  as  bronze  statuettes,  needles, 
rings  of  electrum,  pieces  of  leaden  framing,  etc.  The  gold 
coins  weighed  in  all  25  grammes,  the  silver  coins  625  grammes, 
but  of  the  bronze  coins  there  were  20,800  grammes,  and  many 
had  disappeared  entirely,  leaving  only  their  impress,  and  form- 
ing shapeless  masses  of  the  products  of  their  decomposition, 
mixed  with  grains  of  sand.  Of  the  minerals  formed  from  the 
bronze,  the  greater  part  came  from  the  copper  (red  copper-ore, 
copper-glance,  chalcopyrite,  peacock-ore,  tetrahedrite,  ataca- 
mite),  and  only  one  from  the  tin — on  a  coin  which  still  showed 
bronze  in  its  interior,  but  was  covered  with  a  white  layer  of 
tin  oxide.  The  action  upon  lead  had  produced  coatings  of  galena 
and  phosgenite,  scales  of  lead  oxide,  and  cerussite.  Iron  had 
not  been  altered  to  ordinary  rust ;  the  product  of  its  oxidation 
contained  silica.  Moreover,  pyrite,  instead  of  the  earthy  black 
sulphide  often  occurring  on  the  surface,  had  been  formed  from 
the  iron,  and  was  found  covering  pebbles  and  grains  of  quartz, 
angular  fragments  of  sandstone,  and  also  some  evidently  arti- 
ficial products,  such  as  flint  knives — thus  indicating  indubitably 
its  recent  origin. 

Strange  to  say,  in  spite  of  the  quantity  of  chlorides  in  the 
water,  and  the  great  affinity  of  silver  for  sulphur,  the  silver  coins 
had  not  been  very  seriously  attacked,  and  their  designs  were 
still  quite  distinct,  when  they  had  not  been  coated  with  sulphides 
from  the  neighboring  bronze  coins.  They  must  have  been  pro- 
tected from  chemical  action  by  something  not  now  determinable. 

4 


52  THE    GENESIS    OF  .  ORE-DEPOSITS. 

Moreover,  iron  and  silica  (or  a  hydrated  silicate)  had  pene- 
trated the  wood  found  in  the  springs. 

"At  Bourbonne,  as  at  Plombieres,  the  intrusive  formations  are  less  than  8 
meters  (28  feet)  below  the  surface  ;  and  yet  they  are  very  different  from  what  we 
are  accustomed  to  see  in  our  laboratories.  A  temperature  was  sufficient  for  them 
which  is  low  in  comparison  with  that  which  obtains  at  greater  depths.  What 
forces  would  we  not  see  at  work,  if  we  were  permitted  to  follow  downward  the 
channels  which  have  been  the  pathway  of  hot  springs  !" — Daubre'e,  op.  tit.,  p.  91. 

Structural  Features  of  the  Deposits  of  Mineral  Springs. — The 
original  conditions  at  the  point  of  outflow  of  mineral  springs 
have  seldom  been  preserved  intact.  Even  when  their  channels 
have  been  successfully  prolonged  through  the  ground-water  to 
the  surface,  erosion,  on  the  one  hand,  has  partially  removed 
them  (since  they  often  emerge  in  valley-bottoms),  or  human 
agency,  on  the  other  hand,  has  variously  disturbed  them  by  di- 
verting, choking,  or  walling  them,  or  by  the  erection  of  build- 
ings with  foundations.  For  our  purpose  it  is  important  to  be 
able  to  show  that,  in  all  channels  extending  to  the  surface  and 
still  uninjured,  a  regular  filling  with  symmetrically  arranged 
mineral  crusts vmay  be  observed. 

Such  a  regular  filling  of  the  fissure-channel  of  a  spring  I 
have  seen  at  the  tufa  mounds  of  the  Bad  of  Arczo  near  Parajd 
in  Transylvania.*  The  filling  of  a  fissure  25  centimeters  (10 
inches)  consists  of  variegated  crusts  of  aragonite,  as  thin  as 
paper,  the  fibers  of  which  are  perpendicular  to  the  walls  of  the 
channel.  The  latest  crusts  are  darker,  and  give  a  bituminous 
odor  when  dissolved  in  hydrochloric  acid;  the  oldest  are  usu- 
ally milky  white,  and  leave  after  similar  treatment  a  residuum 
of  gelatinous  silica.  The  water  tastes  very  unpleasantly  salt  and 
bitter.  The  gas  which  hisses  from  the  depths  of  the  fissure  is 
doubtless  mainly  carbonic  acid,  perhaps  with  an  admixture  of 
hydro-carbon. 

Since  the  drawing  of  the  mouths  of  Steamboat  Springs  given 
by  Le  Conte  (op.  cit.,  p.  423)  may  not  be  entirely  comprehensi- 
ble, I  introduce  in  Fig.  8  an  ideal  section  of  one  of  the  spring- 
mounds  of  Arczo. 

It  is  only  the  channel  which  is  filled  with  solid,  almost  trans- 
parent crusts ;  the  deposits  on  the  side  of  the  mound  are  a 

*  F.  Posepny.  "  Studien  aus  dem  Salinargebiete  Siebenbiirgens,"  Jahrb.  d.  k.  k. 
geol.  Reichsanstalt,  Vienna,  1867,  xvii.,  p.  477. 


THE    GENESIS    OF    ORE-DEPOSITS.  53 

fine-grained,  white  lime  mass,  and  in  the  less  immediate  vicin- 
ity of  the  springs  there  are  in  many  places  horizontal  layers  of 
a  lime  tufa,  containing  plant-remains. 

Pigeon  and  Yoisin  describe  an  analogous  but  much  larger 
phenomenon  in  Vichy,  at  the  rocher  des  Celestins,  where  an 
almost  vertical  aragonite  filling,  2  meters  (6.5  feet)  wide  and 
200  meters  (650  feet)  long,  with  fibers  perpendicular  to  the 
planes  of  the  crusts,  may  be  observed  (Daubree,  op.  tit.,  p. 
159). 

The  waters  flowing  away  from  mineral  springs  likewise 
make  solid  deposits,  which  often  form  horizontal  layers,  cover- 
ing considerable  areas.  These  are  the  so-called  travertines — 
formations  analogous  to  the  Carlsbad  Sprudel-  or  Erbsenstein, 
etc.  But  we  are  concerned  at  this  point  with  the  deposits  in 
the  spring-channel  itself  and  in  its  immediate  vicinity,  includ- 
ing not  merely  the  crusts  upon  the  walls  proper,  but  also  those 
surrounding  large  or  small  fragments  of  rock  within  the  chan- 
nel. Many  such  deposits  are  characterized  by  the  pisolite 
formation,  which  we  may  observe  also  in  ore-deposits  (concre- 
tionary iron-ores,  etc.).  These  pisolites  are  evidently  incrusted 
kernels,  the  crusts  being  proportionately  much  thicker  than 
the  kernels.  The  Carlsbad  Sprudelstein  shows,  indeed,  the 
same  structure  on  a  small  scale  as  many  ore-deposits  exhibit  on 
a  large  scale.  The  pisolites,  like  those  of  Tivoli  and  Hamman 
Meskoutine,  consist  of  lime  carbonate,  pure  or  slightly  inter- 
mixed with  iron  oxide  and  silica.  At  the  last-named  locality 
pyrite  occurs  between  the  layers  of  carbonate,  so  that  the 
formation  must  be  pronounced  to  be  crusts  of  lime  carbonate 
and  pyrite  upon  a  foreign  nucleus,  which  was  elevated  and  en- 
crusted so  long  as  the  ascending  column  of  the  spring  had 
energy  enough  to  move  it. 

A  few  words  may  be  well  added  here  concerning  the  Carls- 
bad Sprudelschale  and  Erbsenstein.  As  is  well  known,  the 
Sprudel  represents  an  action  like  that  of  geysers,  ejecting  ther- 
mal water  and  steam  to  a  considerable  height.  The  precipitate 
at  the  present  time  is  a  porous,  somewhat  ferruginous  aragon- 
ite or  travertine  mass.  The  ground  from  which  the  Sprudel 
breaks  forth  is  composed  of  horizontal  layers  of  a  much 
denser  aragonite  mass,  which  can  be  polished,  and  furnishes 
material  for  artistic  lapidary-work.  A  part  of  the  town  of 


54  THE    GENESIS    OF    ORE-DEPOSITS. 

Carlsbad  stands  on  this  so-called  Sprudelschale,  from  which  new 
thermal  springs  sometimes  break  out,  and  the  structural  history 
of  which  may  have  been  like  that  of  the  rising  succession  of 
basins  at  the  Mammoth  Hot  Springs  of  Gardiner  river,  in  the 
Yellowstone  National  Park. 

Certain  layers  of  this  Sprudel-deposit  are  exclusively  aggre- 
gates of  pisolites  of  pea-size,  whence  the  name  Erbsenstein  (pea- 
stone).  Evidently  these  have  been  formed,  like  those  of  the 
Hamman  Meskoutine  spring,  immediately  at  the  outflow  of 
the  mineral  water.  The  precipitate  from  the  solution  (at  the 
moment  supersaturated)  was  deposited  around  individual  rock- 
grains,  which  had  found  their  way  into  the  spring,  to  be  for 
awhile  kept  in  motion  by  its  current.  Successive  crusts  were 
thus  deposited,  until  the  pisolite  became  too  large  to  follow  the 
movement  of  the  spring  and  sank  to  the  bottom,  where  its  ac- 
cessible surfaces  received  still  further  precipitate-crusts.  It 
might  easily  occur,  that  single  cavities  might  remain,  into 
which  the  precipitate  could  not  penetrate.  These  would  repre- 
sent, according  to  our  terminology,  the  central  druse.  Fig.  12 
illustrates  this  process,  while  Fig.  13  shows  a  single  pisolite, 
including  py rite-crusts,  from  Hamman  Meskoutine. 

I  have  had  opportunity  to  see  a  completely  analogous  result 
produced  by  falling  drops  at  Offenbanya,  where,  at  certain 
points  in  an  adit  abandoned  for  some  thirty  years,  water  rich 
in  lime  carbonate  trickled  from  the  roof,  forming  upon  the 
floor  a  deposit  several  centimeters  thick.  At  the  spot  where 
the  drops  fell  directly  upon  the  floor,  a  small  basin-like  depres- 
sion was  formed,  in  which  lay,  like  eggs  in  a  bird's  nest,  various 
bodies  like  pisolites,  consisting  of  a  sand-grain  at  the  center, 
surrounded  by  concentric  crusts  of  carbonate.  Some  of  these 
formations  lying  in  the  middle  of  the  nest  were  quite  loose,  so 
that  they  were  turned  over  by  the  force  of  the  falling  drops, 
which  explained  the  tolerably  uniform  incrustation  upon  them. 
Others  situated  near  the  edge  were  already  fixed,  could  not 
move  any  longer,  and  showed  at  points  a  deposit  of  sinter* 
(Figs.  14  and  15).  Similar  formations,  known  as  "  birds'  nests," 
are  described  by  Schmidt  in  the  old  mine-workings  of  Blegels- 
dorf  and  Bieber.f  Such  formations  appear  to  be  by  no  means 

*  F.  Posepny,  "Ueber  concentrisch-schalige  Mineralbildungen,"  k.  Akad.  d. 
Wissensch,  Vienna,  1868.  f  Beitrage  zu  der  Lehre  von  den  Gdngen,  p.  42. 


THE    GENESIS    OF    ORE-DEPOSITS.  55 

rare  in  metal-mines.  I  found,  for  instance,  in  Oftenbanya,  at 
the  face  of  a  level  which  had  been  abandoned  for  some  years, 
that  small  chips  of  rock  had  been  covered  by  the  falling  drops 
with  two  separate  thin  crusts :  first,  a  white  lustrous  smithson- 
ite,  and  thereupon  a  black,  easily-detached  crust  of  a  manga- 
niferous  substance.*  (Fig.  16.)  The  pisolitic  bodies  formed  by 
falling  drops  are  not  easily  confounded  with  those  formed  by  a 
flowing  spring,  and  when  such  are  found  in  the  interior  of  an 
ore-filling,  they  cannot  well  be  ascribed  to  drippings. 

Pisolitic  forms  appear  in  many  ore-deposits.  Thus  the  cala- 
mine-deposit  of  Santander  in  Spain  betrays  an  oolitic  structure, 
and  I  have  observed  in  the  gold-mines  of  Yerespatak  pisolitic 
forms,  the  kernel  being  an  aggregation  of  gold,  and  the  sur- 
rounding thin  crusts,  carbonates  of  lime,  manganese  and  iron. 
To  this  subject  I  shall  recur. 

From  what  has  been  said  concerning  the  structural  relations 
of  mineral-spring  deposits,  it  appears  that  at  the  mouths  of 
such  springs  phenomena  are  shown,  such  as  crustifications  of 
wall-deposits,  pisolitic  forms,  etc.,  which  we  meet  frequently  in 
ore-deposits  also — an  additional  reason  for  declaring  the  latter 
to  have  been  formed  by  mineral  springs. 

5.  ORIGIN  OF  ORE-DEPOSITS  IN  THE  DEEP  EEGION. 

We  have  seen  that  the  mineral  springs  which  ascend  to  the 
surface  are  dilute  metallic  solutions,  and  that  at  their  outflow 
(the  only  point  where  we  can  directly  observe  their  activity) 
they  form  deposits,  containing  metals,  among  other  things,  and 
exhibiting  a  structure  which  occurs  in  ore-deposits  likewise. 
We  have  followed  to  a  not  inconsiderable  depth  one  ore-de- 
posit which  occurs  upon  an  ascending  spring,  and  have  found 
that,  apart  from  changes  conditioned  by  the  vicinity  of  the  sur- 
face, it  continues  its  character.  Finally,  we  have  encountered 
mineral  springs  in  many  places  where  mining  has  followed  ore- 
deposits  in  depth.  Joining  these  several  links  of  observation, 
we  cannot  avoid  the  conclusion  that  the  ore-deposits  found  in 
the  deep  region  are  the  products  of  mineral  springs,  the  more 
so  since  many  of  them  have  a  structure  and  form  which  can 
only  be  explained  as  the  result  of  precipitation  from  liquids 

*  See  my  paper  on  crustified  mineral  formations,  cited  above. 


56  THE    GENESIS    OF    ORE-DEPOSITS. 

circulating  in  channels.  The  deposits  from  these  liquids  con- 
tain substances  which  are  foreign  to  the  surface  and  to  the 
shallow  region,  and  hence  could  not  have  been  brought  into 
circulation  by  the  descending  ground-water,  but  must  have 
come  from  a  deep  region,  where  higher  temperature  and  pres- 
sure (the  two  factors  increasing  the  solubility  of  all  substances) 
exist. 

Comparing  the  average  density  of  the  earth  (which  is,  ac- 
cording to  the  very  recent  and  careful  investigations  of  R. 
von  Sterneck,*  5.6)  with  the  average  density,  2.5,  of  the  rocks 
forming  the  earth's  crust,  we  must  admit  that  in  the  central 
mass  substances  much  denser  than  5.6  have  been  accumulated, 
that  is  to  say,  the  deep  region  is  the  peculiar  home  of  the  heavy 
metals. 

If  we  imagine  ourselves  standing  in  the  deep  region  in  front 
of  the  profile  of  an  ore-lode,  like  the  Adalbert  at  Przibram, 
for  instance,  1110  m.  (3600  feet)  below  the  surface  and  564  m. 
(1850  feet)  below  sea-level,  we  perceive  a  fissure-space  of  dis- 
cission,  filled  with  symmetric  mineral  crusts,  chiefly  argentif- 
erous lead  sulphide.  Remembering  that  this  filling  has  been 
stoped  continuously  to  the  surface,  we  can  find  no  other  satis- 
factory explanation  than  the  hypothesis  that  it  was  brought  up 
from  still  greater  depths,  and,  in  view  of  the  comparative  in- 
solubility and  the  large  quantity  of  the  metallic  sulphide  here 
accumulated,  it  must  have  been  deposited  from  perpetually  re- 
newed, and,  therefore,  from  ascending,  mineral  solutions.  Who- 
ever has  had  opportunity  to  study  an  ore-lode  in  the  deep  re- 
gions can  conceive  no  other  explanation.  The  miners  them- 
selves have  always  held  this  opinion;  in  other  words,  they 
have  all  been  ascensionists.  In  the  case  of  ore-deposits  occupy- 
ing tubular  channels  in  soluble  rocks,  the  origin  of  these  spaces 
is  not  at  once  clear ;  and  it  has  thus  happened  that  one  or  an- 
other observer,  misunderstanding  the  analogy  of  the  substance 
and  the  conditions  of  filling,  has  suggested  a  different  hypoth- 
esis, as,  for  instance,  S.  F.  Emmons,  whose  conclusions  as  to 
the  Leadville  deposits  I  shall  take  the  liberty  of  controverting 
in  a  later  part  of  the  present  paper.  I  do  not  deny  that  there 

*  I  would  call  attention  to  the  labors  of  v.  Sterneck,  pursued  upon  this  point 
for  a  decade,  and  described  in  the  Mittheilungen  des  k.  k.  Militdr.  Oeograph.  Insti- 
tutes, in  Vienna. 


THE    GENESIS    OF    ORE-DEPOSITS.  57 

are  ore-deposits  permitting  such  a  different  explanation,  but 
they  occur  in  the  shallow  region  only,  and  not  in  the  deep 
region. 

In  the  two  groups  of  ore-deposits  already  discussed,  and 
formed  in  pre-existing  spaces,  a  distinct  crustification  leaves  no 
doubt  as  to  the  manner  of  filling.  Where  crustification  is  ob- 
scure or  absent,  it  is  indeed  not  possible  at  once  to  offer  this 
convincing  proof  of  the  manner  of  deposition.  Recourse  must 
then  be  had  to  the  analogy  of  the  substances  and  their  para- 
genesis.  If  these  correspond  with  the  contents  of  spaces  filled 
with  crusted  deposits,  a  similar  origin  must  be  inferred ;  that 
is  to  say,  even  in  cases  in  which  mineral  solutions,  ascending 
from  the  deep  region,  found  no  open,  continuous  channels,  but 
were  forced  to  create  the  necessary  space  by  the  removal  of  a 
previously-existing  material,  the  conditions  of  the  deep  circu- 
lation still  controlled.  From  these  considerations  it  follows 
that  all  the  deposits  of  the  deep  region  are  referable  to  one 
general  ruling  process,  clearly  shown  to  be  the  action  of  as- 
cending mineral  solutions;  that  is,  they  were  all  formed  by 
ascension. 

This  conception  is  diametrically  opposed  to  the  view  re- 
cently suggested  by  Dr.  F.  Sandberger,  that  ore-deposits  are 
formed  by  so-called  lateral  secretion.  This  view  was  at  first 
asserted  to  be  universally  applicable.  Afterwards,  the  author 
characterized  it  as  holding  good  for  the  majority  of  ore-veins 
only,  and  restricted  it  by  the  following  definition : 

"The  theory  of  lateral  secretion  was  conceived  in  this  sense  only,  that  the 
material  for  the  filling  of  veins  is  derived  from  the  country-rock  through  gradual 
leaching  by  seepage-water  (Sickerwasser),  which  brings  the  dissolved  substance 
from  both  sides  to  the  vein-fissure,  where  it  is  then  converted  by  chemical  decom- 
positions into  insoluble  gangue-minerals  and  ores,  and  so  deposited."* 

It  will  be  seen  that  he  started  from  the  wholly  erroneous 
assumption  that  the  ore-veins  of  the  deep  region  stood  open 
(like  the  fissures  in  a  rock  upon  the  surface),  so  that  seepage- 
water  from  both  sides  could  deposit  material  in  them.  That 
is,  he  conceived  of  a  fissure  containing  air  only,  and  forgot 
entirely  that  such  open  fissures  are  found  exclusively  above  the 

*  F.  Sandberger,  Untersuchungen  uber  Erzgange,  2tes  Heft,  Wiesbaden,  1885,  p. 
159. 


58  THE    GENESIS    OF    ORE-DEPOSITS. 

ground-water  level,  below  which  every  newly-formed  fissure 
must  be  immediately  filled  with  water.  The  term  sickern  cor- 
responds with  the  English  "  seep,"  "  trickle,"  or  "  drop,"  and 
can  only  be  understood  as  describing  the  downward  movement 
of  a  small  quantity  of  liquid.  It  is  thus  impossible  to  suppose 
that  Sandberger's  meaning  has  been  misunderstood ;  and  we 
are  forced  to  conclude  that  he  boldly  extended  his  conclusions 
to  cover  a  region  with  the  physical  conditions  of  which  he  was 
unacquainted. 

A  lateral  secretion  in  this  sense  is,  as  I  have  elsewhere  shown,* 
possible  above  the  ground-water  level  only.  It  is  indeed  con- 
ceivable that  even  in  the  deep  region  isolated  spaces  may  exist, 
from  which  accumulated  gases  find  no  way  to  the  surface,  and 
in  which  formations  may  occur  similar  to  those  in  cavities  above 
water-level ;  but  such  instances  (as  at  Wiesloch,  in  Baden,  and 
Raibl,  in  Carinthia)  are  demonstrably  exceptions  to  the  general 
rule  above  stated. 

What  interests  us  most  is,  that  in  order  to  establish  his 
theory,  Sandberger  was  forced  to  discredit  the  fact  of  actual 
deposition  in  the  channels  of  mineral  springs.  The  proof  of 
this  fact  at  Sulphur  Bank  and  Steamboat  Springs  was  highly 
inconvenient.  Since,  as  he  had  said,  "  waters  which  flow  with 
such  rapidity  as  that  of  ascending  mineral  springs  containing 
carbonic  acid  are  shown  by  experience  to  produce  no  deposits 
in  their  channels,  but  to  do  this  only  in  the  immediate  vicinity 
of  their  outflow  "  (op.  tit.,  p.  5),  he  was  not  convinced  by  the 
conditions  shown  at  Steamboat  Springs,  where  the  deposits  are 
near  the  outflow.  With  regard  to  Sulphur  Bank,  he  was  not 
acquainted  with  the  works  of  Le  Conte  and  G-.  F.  Becker, 
showing  that  the  ore-deposit  is  found  in  the  channel  itself. 
Although  he  did  not  doubt  "  that  ore-deposits  are  here  observed 
in  process  of  formation "  (1.  c.,  p.  13),  he  recalled  the  well- 
known  solubility  of  mercury  sulphide  in  alkaline  sulphides ; 
argued  that  "  the  leaching  of  pre-existing  quicksilver-deposits 
by  alkaline  sulphides  presents  no  difficulty"  (1.  c.,  p.  15);  and 
was  inclined  to  believe  that  the  cinnabar-deposits  near  the  out- 
flow were  referable  to  older  ones.  Endeavoring  thus  to  render 
harmless  the  two  instances  unfavorable  to  the  lateral-secretion 

*  "Ueber  die    Bewegungsrichtung    der   unterirdisch    circulirenden   Flussig- 
keiten." — Comptes  rend,  de  la  session  du  Congres  geol.  internat.,  Berlin,  1885. 


THE    GENESIS    OF    ORE-DEPOSITS.  59 

theory,  he  summed  up  his  consideration  of  them  at  that  time 
with  the  remark  that  "  in  California  no  proof  is  presented  of 
the  formation  of  ore-veins  by  ascending  springs  "  (op.  cit.,  p. 
16).  After  reading  Le  Conte's  account  he  returned  to  the  sub- 
ject in  the  second  part  of  his  work,*  asserting  (p.  162)  that  in 
the  numerous  excavations  connected  with  the  walling-in  of  min- 
eral springs,  it  has  never  been  observed  that  hot  springs  have 
deposited  "  metals "  in  the  immediate  vicinity  of  their  chan- 
nels. He  confesses  again  (p.  161)  that  here  is  "  unquestionably 
an  ore-deposit,  formed  by  the  precipitation  of  silica  and  cin- 
nabar from  a  hot  alkaline  sulphur-spring,  which  has  found  and 
dissolved  mercury  sulphide  somewhere  below;"  and  admits 
that  hot  alkaline  sulphur-waters  may  precipitate,  besides  quick- 
silver, also  gold,  tin,  bismuth,  arsenic,  and  antimony, — but  not 
copper,  silver,  and  lead-ores,  which  are  often  associated  with 
the  foregoing.  These,  he  says,  cannot  have  been  deposited 
from  hot  alkaline  sulphur-springs.  "  There  is,  therefore  (p. 
162),  no  reason  in  the  conditions  of  Sulphur  Bank  for  restor- 
ing the  ascension  theory  to  its  former  authority  in  the  science 
of  ore-veins." 

It  will  be  seen  that  his  chief  argument  is,  that  according  to 
his  opinion,  no  metallic  deposit  has  ever  been  found  in  the 
channel  of  a  spring,  for  he  seems  not  to  consider  as  conclusive 
the  deeper  workings  at  Sulphur  Bank.  Such  a  sweeping  asser- 
tion is  easy;  for  it  is  not  likely  that  in  walling  a  mineral 
spring  excavations  will  be  carried  deep  enough  to  reveal  the 
condition  of  its  channel  proper. 

Sandberger's  contention  comprises  two  propositions :  (1) 
Metals  have  been  found  hitherto  only  in  the  ocherous  deposits 
from  mineral  springs;  and  (2)  in  walling  mineral  springs,  de- 
posits formed  in  their  channels  have  not  yet  been  found. 
These  two  assertions  are  not  controverted ;  but  the  conclusion, 
that  because  hitherto,  in  digging  out  mineral  springs,  we  have 
found  no  metals  in  their  channels,  therefore  they  cannot  be  de- 
posited in  the  channels,  but  only  at  the  outflow,  is  illogical. 

Excavations  for  the  walling  of  mineral  springs  do  not  extend 
to  the  channels  of  the  deep  region.  Heavy  pumping  is  re- 
quired to  penetrate  even  a  few  meters  below  the  ground-water 

*   Untersuchungen  uber  Erzgange,   Wiesbaden.     First  part,    1882 ;   second  part, 

1885. 


60  THE    GENESIS    OF    ORE-DEPOSITS. 

level ;  whereas,  to  decide  this  question,  a  depth  must  be  reached 
at  which  the  ascending  spring  is  not  altered  by  the  descending 
ground-water,  the  oxidation  and  chlorination  due  to  surface 
agencies  no  longer  appear,  etc. 

We  know  that  temperature  and  pressure,  the  two  great  fac- 
tors of  solubility,  are  continually  diminished  as  the  surface  is 
approached;  and  we  can  directly  observe  one  result  of  this 
change  in  the  liberation  of  the  carbonic  acid  absorbed  at 
greater  depths.  Why  should  not  the  substances  rendered  in- 
soluble by  the  decrease  of  these  factors  be  deposited  in  the 
channels  ?  If  no  such  deposition  has  occurred,  then  the  pre- 
cipitates must  have  been  carried  upward  by  the  current,  and 
should  be  separable  by  filtration  from  the  water.  GT.  F.  Becker, 
in  filtering  the  Steamboat  Springs  water  before  analysis,  found 
(1.  c.,  p.  346)  in  the  filtrate  a  precipitate  of  antimony  and 
arsenic  sulphides,  with  silica,  which  he  ascribes  to  the  fall  of 
temperature  and  the  action  of  low  forms  of  plant-life. 

But  we  find  in  various  closed  conduits  of  mineral  water — 
i.e.,  in  artificial  channels — that  deposits  are  formed,  not  only  at 
the  mouth,  but  also  in  the  channel  itself.  Why  should  natu- 
ral channels  form  an  exception  ? 

I  think  it  has  been  shown  that  Dr.  Sandberger's  chief  objec- 
tion to  the  formation  of  ore-deposits  by  ascending  mineral 
springs  is  without  foundation,  and  that  the  entire  chain  of  phe- 
nomena corroborates  our  explanation.  But  the  lateral-secre- 
tion theory  of  Sandberger  suffers  from  several  other  funda- 
mental defects,  which  I  cannot  avoid  indicating  in  this  place, 
because  that  theory  was  for  a  while  accepted  as  a  simple  and 
welcome  explanation  of  the  genesis  of  ore-deposits,  and  began 
to  hinder  the  progress  of  knowledge  on  that  subject. 

It  found  many  disciples,  especially  among  mineralogists,  be- 
cause it  permitted  the  most  extensive  genetic  generalizations, 
without  requiring  the  observer  to  leave  his  mineral  collection 
and  laboratory,  to  descend  into  the  mine,  and  to  study  the  ore 
in  the  place  of  its  origin.  On  the  other  hand,  it  must  be  con- 
fessed that  the  promulgation  of  this  theory  led  to  many  inves- 
tigations of  rocks,  which  will  be  useful  to  science  in  other 
directions. 

Sandberger,  being  convinced  that  he  had  detected  foreign 
admixtures  of  the  metals  in  silicates,  felt  himself  warranted  in 


THE    GENESIS    OF    ORE-DEPOSITS.  61 

explaining  by  his  theory  all  ore-deposits  in  the  silicate  rocks ; 
but  he  could  not  so  well  deal  with  those  in  limestone,  which 
were  cited  by  Stelzner  as  a  chief  argument  against  the  univer- 
sality of  his  conclusion.*  With  regard  to  Raibl,  in  Carinthia, 
it  occurred  to  him  to  examine  the  marly  slates  (Mergelschiefer) 
overlying  the  limestone ;  and  finding  in  these,  besides  traces 
of  Li,  Cr,  and  Cu,  more  considerable  quantities  of  Pb  and 
Zn,  he  concluded  that  the  metals  in  the  ore-channels  of  the 
limestone  under  these  slates  had  been  leached  out  of  the  latter 
(op.  cit.,  p.  34).  This  was  already  a  descending,  and  not  a  lat- 
eral secretion. 

In  a  paper  upon  the  applicability  to  this  case  of  the  lateral- 
secretion  theory, f  however,  I  pointed  out  that  also  below  the 
ore-bearing  limestone  of  Raibl,  at  Kaltwasser,  there  are  sili- 
cate rocks,  which  probably  contain  likewise  minute  quantities 
of  metal,  and  that  if  Sandberger  had  successfully  analyzed 
these,  he  would  have  been  obliged  to  assume  an  ascent.  In 
the  same  paper  I  argued  that  the  lateral-secretion  theory  does 
not  account  for  the  sulphur  and  the  metallic  sulphides;  and  I 
brought  forward  for  discussion  the  veins  of  Przibram,  assum- 
ing that  in  that  district,  where  sedimentary  rocks  are  traversed 
by  heavy  eruptive  masses,  Sandberger  could  consider  the  latter 
only  as  the  original  source  of  the  metals  in  the  veins.  From 
average  analyses  for  the  latest  year  of  production,  I  calcu- 
lated that  each  square  meter  (10.75  square  feet)  of  vein-sur- 
face stoped  represented  190  kilogrammes  (426  Ibs.)  of  me- 
tallic sulphides,  or  in  detail : 

Pb.         Zn.      Fe.       Cu.         Ag.  S.  Sb.         As. 

Kilogrammes,      132        13        5        0.3        0.8        34.6        2.5        3.7 

If  these  substances  had  been  derived  by  lateral  secretion 
from  the  country-rock  (the  eruptive  mass  being  30  meters 
thick  by  the  main  vein,  or  100  meters  for  the  whole  group  of 
veins)  there  must  needs  have  been  in  each  cubic  meter  (35 
cubic  feet)  of  the  country-rock  1.9  to  6.3  kilogrammes  (4  to 
14  pounds)  of  metallic  ingredients — a  quantity  not  to  be  called 
minute.  Or,  reversing  the  calculation,  and  starting  with  the 
largest  proportion  of  metal  ever  found  in  these  eruptive  rocks, 

*  A.  Stelzner,  Jahrb.f.  Min.,  1881,  p.  209. 

t  Oester.  Zeitsch.  f.  B.  u.  H.,  1882,  xxx.,  p.  607. 


62  THE    GENESIS    OF    ORE-DEPOSITS. 

it  would  have  required  more  than  one  hundred  times  the  thick- 
ness of  such  rocks  actually  present  in  the  district  to  supply  the 
contents  of  the  veins.  By  these  calculations  and  other  argu- 
ments, I  showed,  as  I  thought,  the  special  inapplicability  of  the 
theory  to  Przibram,  but  I  expressed  a  willingness  to  examine 
some  of  the  eruptive  dikes  for  minute  metallic  admixtures, 
preferring  only  that  such  an  examination  should  be  checked  by 
another  person. 

The  management  of  the  government  mining  department  en- 
trusted to  the  chemist,  A.  Patera,  the  investigation  of  individual 
samples  of  Przibram  rock,  but  also  called  Dr.  F.  Sandberger  to 
Przibram,  where  the  first  tests  were  executed  with  the  aid  of 
a  Commission,  of  which  I  was  a  member.* 

Unfortunately  an  ailment  of  the  eyes  forced  me  to  inactivity, 
and  I  could  do  little  on  the  Commission. 

Dr.  Sandberger  submitted  a  statement  (op.  cit.,  pp.  305-327) 
or  compilation,  from  which  it  appeared  that  he  attached  less 
importance  to  the  analysis  of  the  eruptive  rocks  than  to  that 
of  the  stratified  rocks,  composed  of  the  detritus  of  the  central 
Bohemian  gneiss  mass.  According  to  this  view,  the  metals  of 
the  Przibram  veins  came  from  the  mica  of  the  gneiss  detritus. 
According  to  Dr.  Sandberger,  however  (op.  cit.,  pp.  362-3),  the 
investigation  disclosed  that  "  an  essential  part  of  the  lead  and 
silver  contents  of  the  ore-veins  is  due  to  the  eruptive  rocks  " — 
which  involves  a  modification  of  the  above  theory. 

Twenty-five  rock-samples,  selected  by  the  Commission,  were 
tested  for  metallic  admixtures  according  to  a  method  agreed 
upon  (but  not  very  strictly  followed)  by  Dr.  Sandberger,  H. 
Freiherr  von  Foullon,  A.  Patera  and  C.  Mann,  with  tolerably 
concordant  results,  although  Patera  in  particular  expressed 
some  doubts  as  to  the  correctness  of  the  method.  This  led 
Prof.  A.  Stelzner  in  Freibergf  to  make  a  thorough  test  of  the 
means  employed,  which  showed  that  Sandberger's  method  can- 
not decisively  determine  whether  the  metals  detected  in  the 


*  "  Untersuchungen  von  Xebengesteinen  der  Przibramer  Gange  mit  Riicksicht 
auf  die  Lateralsecretionstheorie  von  Dr.  F.  V.  Sandberger,  ausgefiihrt  1884-7  und 
veroffentlicht  im  Auftrage  Seiner  excellenz  des  k.  k.  Ackerbauministers  J.  Graf  en 
von  Falkenhayn."  —  B.  u.  H.  Jahrb.  d.  k.  k.  Bergakad.,  etc.,  xxv.,  1887,  p.  299. 

f  A.  Stelzner,  "Die  Lateralsecretionstheorie  und  ihre  Bedeutung  fur  das  Przi- 
bramer Ganggebiet. " — Jahrbuch  der  k.  k.  Bergakad.,  1889,  p.  1. 


THE    GENESIS    OF    ORE-DEPOSITS.  63 

silicate  were  original  constituents,  or  whether  they  are  not 
secondary  impregnations,  left  undissolved  by  the  reagents  em- 
ployed. 

It  is  thus  rendered  probable  that  minute  metallic  admixtures 
detected  in  the  country-rock  by  Sandberger's  method  are  really 
derived  from  the  ore-deposit,  i.e.9  are  not  idiogenous  but  xenog- 
enous.  His  assumptions  in  this  field  also  are  thus  shown  to  be 
indefensible. 

While  I  acknowledge  fully  the  great  importance  of  chemical 
data  for  the  explanation  of  vein-phenomena,  I  cannot  give 
here,  without  becoming  too  prolix,  all  the  chemical  views,  often 
quite  discordant,  and  must  content  myself  with  the  description 
of  a  theory  of  ore-deposits  based  upon  purely  chemical  grounds, 
which  has  just  been  made  public  by  De  Launay.  The  author 
starts  chiefly  from  the  views  of  Elie  de  Beaumont*  concerning 
volcanic  and  metallic  emanations,  adding  to  these  the  results 
of  the  studies  of  Fouque,  Senarmont,  Ebelmen,  St.  Claire  De- 
ville,  Daubree,  etc.  He  begins  with  the  primitive  occurrence 
of  magnetite  in  the  eruptive  rocks,  which  he  extends  to  many 
other  metals  a"nd  minerals  whose  primitive  presence  in  erup- 
tives  has  not  been  demonstrated.  Certain  metallic  substances 
were  segregated  in  cooling  from  the  molten  mass ;  others  have 
been  dissolved  from  the  eruptive  rock  in  depth  by  "  mineral- 
izers,"  such  as  emanations  of  chlorine,  fluorine,  sulphur,  etc., 
and  have  been  deposited  in  the  channels  leading  to  the  sur- 
face. De  Launay  is  a  very  positive  ascensionist ;  he  also  doubts 
the  primitive  deposition  of  ores  in  marine  basins,  and  thus 
comes  by  the  path  of  chemical  speculation  to  results  analogous 
to  mine.  Volcanic  and  ancient  eruptive  rocks ;  fumaroles  and 
mofettes ;  geysers  and  thermal  springs — these  indicate  the  ways 
by  which  the  metals  have  reached  the  earth's  surface.  But  of 
such  assumptions  we  must  obtain  assurance  through  observa- 
tions in  other  directions.  Views  based  upon  purely  chemical 
conclusions  are  not  sufficiently  convincing  for  us,  because  they 
are  gained  in  the  chemical  laboratory  under  conditions  different, 
especially  as  to  pressure  and  temperature,  from  those  which 
obtain  in  the  deep  region. 

*  Elie  de  Beaumont,  Bulletin  de  la  Soc.  geol.  de  France,  2  ser.,  iv.,  p.  1249. 


64  THE    GENESIS    OF    ORE-DEPOSITS. 

Manner  of  Filling  of  Open  Spaces  in  General. 

We  know  already  that  cavities,  however  originated,  are 
always  filled  in  analogous  ways.  We  find  in  vein-spaces,  in 
the  spaces  of  dissolution,  and  even  in  individual  geodes  of  opal 
and  chalcedony,  always  the  same  elements  of  structure,  though 
in  the  most  widely  different  materials. 

Considering  the  matter  closely,  we  find  that  many  things 
are  peculiar  to  the  shallow  region,  as  the  nearest  to  atmos- 
pheric influences ;  but  some  things  experienced  in  that  region 
may  be  used  to  explain  the  phenomena  of  deposits  in  the  deep 
region  also. 

Since  we  have  seen  that  the  precipitate  in  an  approxi- 
mately horizontal  pipe,  entirely  filled  with  liquid,  attaches 
itself  to  the  whole  interior  surface,  the  same  must  be  true  for 
an  underground  channel,  and  all  the  more  if  it  approaches  a 
vertical  position.  Under  such  circumstances  the  deposit  or 
mineral  crust  will  cover  uniformly  the  whole  wall-surface. 

Evidently  the  same  laws  govern  here  as  in  sedimentation. 
When  the  section  of  the  passage  through  which  the  liquid 
flows  under  a  given  pressure  is  relatively  small,  the  deposit 
will  take  place  only  when  the  passage  is  enlarged.  This  ex- 
plains the  sometimes  unequal  distribution  of  ore  in  one  and  the 
same  mineral-water  channel. 

As  in  a  saturated  solution  a  precipitate  may  be  obtained  upon 
any  solid  body  introduced,  so  in  our  mineral-water  channels 
deposits  will  be  made  upon  all  solid  bodies — splinters  or  masses 
of  rock  fallen  into  the  fissure,  loose  pieces  of  older  mineral 
crusts,  and  individual  crystals  floating  in  the  liquid. 

The  size  of  the  rock-fragments  here  considered  is  very  varia- 
ble. We  might  include,  for  instance,  those  which  are  inclosed 
between  two  regular  vein-branches.  But  we  will  narrow  our 
view  to  what  can  be  seen  from  a  single  standpoint  in  the  mine, 
and  then  we  observe  that  horses  of  several  square  meters'  sur- 
face are  uniformly  crusted,  like  small  pieces  of  country-rock 
found  in  the  vein-filling,  the  only  difference  being,  perhaps, 
that  the  crusts  are  thicker  and  more  numerous  upon  the  larger 
masses.  The  fragments  of  rock,  either  angular  or  already 
more  or  less  rounded,  form,  when  incrusted,  the  so-called 
sphere-,  cocarde-,  or  ring-ores.  Crusted  rock-kernels  may  often 
be  observed  coexisting  with  distinct  wall-crusts.  Sometimes 


THE    GENESIS    OF    ORE-DEPOSITS.  65 

the  latter  are  less  prominent  than  the  former,  and  the  ore-de- 
posit then  has  the  appearance  of  a  breccia  or  a  conglomerate, 
the  several  fragments  of  which  are  held  together  by  the  min- 
eral crusts.  If,  on  the  plane  of  a  given  section,  there  appear 
no  points  of  contact  between  the  fragments,  it  must  not  be 
concluded  that  they  originally  hung  free  in  the  vein-space,  or 
that  they  have  been  pressed  apart  at  a  later  period  by  the  force 
of  crystallization  of  the  mineral  crusts,  for  the  actual  points  of 
contact  can  be  found  in  a  parallel  section;  at  least,  I  have 
always  found  them  when  I  have  sliced  into  plates  a  specimen 
on  the  surface  of  which  they  were  not  shown.  I  mention  this 
circumstance  because  many  extensive  discussions  have  been 
based  upon  imperfect  views  of  single  sections,  giving  deceptive 
indications  of  structure.* 

I  w^ould  recommend  the  frequent  preparation  of  sections  and 
slides  of  such  apparently  complicated  structures,  and  I  am  con- 
vinced that  seeming  contradictions  and  difficulties  would  be 
simply  explained  thereby.  It  is  only  a  question  of  correct  ob- 
servation and  representation,  for  which,  it  must  be  confessed, 
the  use  of  coloring  may  be  necessary.  In  this  connection  I 
must  remark  that  illustrations,  erroneous  in  this  respect,  have 
found  their  way  even  into  text-books,  as,  for  instance,  the  pic- 
ture of  cocarde-oil  given  by  Cotta,f  which  is  taken  from  a  care- 
ful but  uncolored  drawing  by  Weissenbach,J  of  which  I  repro- 
duce a  part  in  Fig.  17.  Fragments  of  mica-slate  are  crusted 
with  layers  of  quartz  and  pyrite,  and  in  the  vugs  there  is  some- 
times also  manganese  or  brown-spar.  The  radial  appearance 
of  the  crusts  in  the  drawing  is  evidently  due  to  the  position 
of  the  crystals  perpendicular  to  the  wall-surfaces,  and  is,  as  a 
rule,  observable  in  all  such  cases.  The  same  figure  from  Weis- 
senbach  has  been  used  by  A.  Daubree  also,§  as  an  instance  of 
a  filon  br&cheform, ;  but  the  several  crusted  rock-fragments  are 
separated  by  heavy  lines,  which  make  the  representation  not 
only  incorrect  but  incomprehensible. 

The  phenomenon  may  be  most  generally  illustrated  by  Fig. 

*  E.g.,  Trans.  A.  I.  M.  K,  1883,  xi.,  119. 

t  Lehre  v<m  den  Erzlagerstatten,  Part  L,  Freiberg,  1859,  p.  33. 

t  G.  G.  A.  von  Weissenbach.  Abbildung  merhviirdiger  Gangverhaltnisse.  Leip- 
zig, 1836,  Fig.  2. 

\  A  Daubree.  Les  eaux  souterraines  aux  epoques  anciennes.  Paris,  1887,  Fig.  24, 
p.  64. 


66  THE    GENESIS    OF    ORE-DEPOSITS. 

18,  which  represents  a  section  through  a  gold-specimen  from 
the  Katrontza  ore-body  at  Verespatak,  and  of  which  I  intend 
to  publish  in  my  monograph  on  the  occurrence  of  gold  in 
Transylvania  a  series  of  parallel  sections  in  color.  Four  peb- 
bles, three  of  quartz-porphyry  and  one  of  mica-slate,  are  regu- 
larly crusted  with  (1)  a  thin  zone  of  horn  stone,  (2)  a  thin  crust 
of  pyrite,  composed  of  several  layers  no  thicker  than  paper, 
(3)  hornstone,  in  which  occurs  (4)  a  zone,  5  mm.  (0.2  in.)  in 
average  thickness,  of  fine  aggregates  of  native  gold,  extending 
often  into  the  next  following  crust  (5)  of  quartz,  containing 
scattered  clouds  of  hornstone.  The  series  ends  in  this  speci- 
men (6)  with  open  central  druses.  But  other  specimens  from 
the  same  deposit  show  also  minute  crusts  of  manganese-spar, 
to  which  I  shall  recur. 

Fig.  11,  representing  the  occurrence  of  cinnabar  in  the 
deeper  workings  at  Sulphur  Bank,  is  an  interpretation  of  the 
description  and  sketch  given  by  Le  Conte  (op.  cit.,  p.  28). 
Fragments  of  sandstone  and  slate  with  somewhat  rounded 
edges  are  regularly  surrounded  with  crusts  of  cinnabar  which 
fill  the  space  between,  up  to  the  central  druse.  Sometimes 
crusts  of  hydrated  silica  and  pyrite  appear  also.  Fig.  10  is  a 
picture  of  a  rich  portion  of  the  surface-workings  of  1874, 
which  I  sketched  at  that  time  in  my  note-book.  The  basaltic 
country-rock  is  thoroughly  cut  up  by  irregular  seams,  which 
have  disintegrated  it  to  a  shaly  mass.  In  the  seams,  especially 
where  they  come  together,  larger  spaces  have  been  formed, 
often  filled  with  decomposed  country-rock,  often  showing 
separate  crusts  of  cinnabar  and  opal,  with  a  central  druse. 
The  porous  material  of  rock  and  filling  is  impregnated  with 
native  sulphur. 

Fig.  19  shows  the  filling  of  a  space  of  dissolution  at  Raibl. 
It  is  a  diagram  from  the  accurate  picture  in  my  monograph 
upon  the  deposit.*  A  nucleus  of  limestone  is  surrounded  by 
innumerable  fine  crusts  of  wurtzite  and  more  compact  but  less 
regular  layers  of  galena. 

Fragments  of  earlier  mineral  crusts,  which  have  been  in 
some  way  separated  from  their  original  position,  are  often 
found  surrounded  by  mineral  crusts  of  later  origin.  An  ex- 

*  "Die  Blei-und  Galmei-Lagerstatten  von  Eaibl  in  Karnthen." — Jahrb.  d.  k.  k. 
geol  E.  Anstalt,  xxiii.,  1873,  Bd.  I.,  Fig.  13. 


THE    GENESIS    OF    ORE-DEPOSITS.  67 

ample  is  shown  in  Fig.  20,  representing  boiler-scale  from  one 
of  the  Przibram  pumping  plants.  Here  fragments  of  disloca- 
ted scale,  about  2  mm.  (0.08  inch)  in  diameter,  are  enveloped 
in  later,  thin  crusts,  and  thus  united  to  a  breccia.  The  mass 
consists  chiefly  of  fibrous  gypsum,  the  fibers  of  which  stand 
perpendicular  to  the  surfaces  to  which  they  are  attached. 

Figs.  21  and  22  present  a  very  distinct  example,  in  which 
earlier  mineral  crusts,  together  with  adhering  pieces  of  country- 
rock,  are  surrounded  by  recent  crusts.  These  figures  are  taken 
from  the  valuable  treatise  of  I.  Ch.  Schmidt,*  and  refer  to  Zel- 
lerfeld  in  the  Hartz,  whence  A.  von  Grroddeck  also  has  ob- 
tained very  interesting  illustrations  of  vein-filling. f 

I  have  seen  a  more  complicated  example  from  the  Katrontza 
ore-body  at  Verespatak,  where  very  rough  ancient  crusts  of 
black  hornstone  and  parti-colored  quartz  have  been  cemented 
together  by  deposits  of  later  quartz  and  manganese  spar  to  a 
compact  mass,  with  some  central  druses.  Similar  conditions 
will  be  seen  to  obtain  in  the  so-called  pipe-ores  of  Raibl, 
Figs.  25  to  28. 

The  variable  relation  between  the  diameter  of  the  nucleus 
and  the  thickness  of  the  surrounding  crust  naturally  contrib- 
utes greatly  to  the  variety  of  the  resulting  appearances.  In 
the  pisolitic  formation,  for  instance,  the  crust  is  many  times 
thicker  than  the  nucleus. 

In  some  cases  the  kernels  are  individual  crystals.  I.  Ch.  L. 
Schmidt  describes  pisolitic  forms  from  Warstein,  in  West- 
phalia, the  kernel  of  which  is  a  crystal  of  yellow  eisenkiesel, 
about  5  mm.  (0.2  inch)  in  diameter,  showing  prismatic  and 
dihexahedric  faces,  and  covered  first  with  a  thin,  white  coating, 
upon  which  are  crusts  of  coarsely  fibrous  eisenkiesel.  The 
edges  of  these  are  gradually  rounded,  until  egg-shaped  sphe- 
roids, about  12  mm.  (0.5  in.)  in  diameter,  are  formed,  touching 
each  other  at  single  points,  and  leaving  interspaces,  which  are 
either  filled  entirely  with  granular  eisenkiesel,  or  contain  resid- 
ual vugs  lined  with  transparent,  finely  crystalline  quartz. 

Fig.  24  represents  the  geologically  important  occurrence  of 

*  I.  Christian  Lebrect  Schmidt. — Beitrage  zu  der  Lehre  von  den  Gdngen,  Sie- 
gen,  1827. 

f  A.  von  Groddeck. — Ueber  die  Erzgdnge  des  Oberharzes.  (Inaugural  dissertation. ) 
Berlin,  1867. 

5 


68  THE    GENESIS    OF    ORE-DEPOSITS. 

crusted  kernels  of  native  gold  from  the  Matyas  Kiraly  mine  at 
Verespatak.  Minute  aggregates  of  native  gold  are  system- 
atically surrounded  by  distinct,  beautifully  pink  to  carmine, 
thin  crusts  of  rhodonite  or  rhodochrosite.  So  long  as  the 
kernels  were  completely  separated,  or  were  kept  suspended  by 
the  disturbance  traversing  the  cavity,  these  crusts  were  depos- 
ited entirely  around  each.  After  they  had  become  fixed,  later 
deposits  of  the  same  sort  covered  them;  then  followed  car- 
bonates of  lime  and  iron ;  and  finally  came  the  quartz,  the 
beautiful  water-clear  crystal-tips  of  which  project  into  the  cen- 
tral druses. 

The  occurrence  of  gold  in  manganese  spar  is  not  rare  at 
Verespatak;  ornaments  cut  from  this  material  are  pretty 
widely  sold.  But  I  have  found  but  once  such  a  distinct  envel- 
opment of  the  gold  by  the  rhodochrosite  crusts.  The  figure 
represents  a  piece  cut  for  a  brooch,  which  is  in  my  wife's  pos- 
session. It  is  specially  interesting,  also,  as  showing  that  the 
gold  was  not  derived  from  the  secondary  decomposition  of  au- 
riferous sulphides  or  tellurides  in  loco,  but  was  directly  precipi- 
tated from  the  mineral  solutions  which  subsequently  deposited 
the  surrounding  crusts. 

We  have  seen  that  within  the  domain  of  vadose  or  shallow 
circulation  peculiar  deposits,  classed  as  stalactites,  are  very  com- 
mon, not  only  in  the  spaces  eroded  by  the  natural  circulation 
of  the  ground-water,  but  also  in  spaces  created  through  the 
artificial  depression  of  the  water-level  by  mining.  In  the  latter 
case,  since  mining  often  follows  ore-deposits  into  the  deep  re- 
gion, a  much  larger  variety  of  substances  is  exposed  to  altera- 
tion, so  that  stalactitic  formations  of  all  kinds  of  materials  may 
be  encountered.  Chiefly,  however,  we  find  in  this  form  the  re- 
sults of  oxidation,  and  it  is  somewhat  exceptional  to  meet  with 
the  products  of  reduction,  effected  by  organic  matter  in  the 
mine.  The  most  frequent  of  these  are  stalactites  of  pyrite. 

This  circumstance  led  to  the  opinion  that  stalactites  in  an 
ore-deposit  should  be  taken  as  characteristic  of  a  vadose  or 
shallow  origin,  through  the  descending  movement  of  the  solu- 
tions which  formed  the  stalactites.  This  view  has  been  most 
clearly  advanced  by  Dr.  A.  Schmidt.*  The  earliest  formations 

*  Die  Zinkerzlagerstatten  von  Wiesloch  in  Baden,  Heidelberg,  1881,  p.  94. 


THE    GENESIS    OF    ORE-DEPOSITS.  69 

in  the  instructive  Wiesloch  deposits  are  the  sulphides,  mar- 
casite,  galena  and  wurtzite,  to  the  decomposition  of  the  latter 
of  which,  through  the  metasomatic  replacement  of  the  carbon- 
ate of  lime  by  the  carbonate  of  zinc,  the  zinc-ore  deposits  are 
due.  These  he  held  to  be  clearly  vadose  in  origin ;  and  since 
the  sulphides  also  occur  in  stalactites,  he  concluded  that  they 
likewise  must  have  been  formed  by  infiltration  from  above. 
The  fact  that  these  latter  formations  now  lie  below  water-level, 
whereas  the  formation  of  stalactites  requires  a  space  filled  with 
air  or  gas,  only  forced  him  to  endeavor  to  explain  this  contra- 
diction by  the  hypothesis  of  suitable  elevations  and  depressions 
either  of  the  water-level  or  of  the  land  itself. 

But  all  this  would  have  been  unnecessary  if  he  had  borne  in 
mind  that  ascending  liquids  under  a  certain  pressure  will  pene- 
trate into  a  cavity  from  all  sides,  and  may  enter  through  the 
roof  if  the  bottom  and  walls  are  less  permeable.  He  distin- 
guishes in  general  two  forms  of  development  in  the  original 
ore-deposition,  namely,  the  filling  of  the  lower  part  of  a  cavity 
with  nearly  horizontal,  undulating  crusts  of  wurtzite,  with  a 
little  galena,  and  the  stalactites  which  hang  from  the  roof,  there 
being  no  discoverable  trace  of  corresponding  stalagmites  below. 
This  indicates  that  the  cavity  was  not  wholly  filled  with  gas, 
but  only  in  its  upper  part,  to  which,  consequently,  the  stalac- 
titic  forms  are  confined.  As  to  the  manner  of  the  later  decom- 
position of  the  wurtzite,  which  extends  down  to  the  present 
water-level,  there  can  be  no  doubt  (op.  tit.,  p.  101). 

Similar  conditions  are  found  in  Raibl,  where  I  have  carefully 
studied  the  stalactites  locally  called  "  pipe-ores."*  I  find  these,  it 
is  true,  not  in  their  original  position  at  the  roof  of  the  cavities, 
but  in  the  midst  of  the  filling,  already  broken  off  and  surrounded 
by  the  latest  mineral  crust,  in  a  dolomite  spar.  They  seem  to 
have  occurred  at  many  points  in  this  deposit,  but  my  observations 
were  confined  to  two,  one  of  which  was  on  the  5th  Johanni  level, 
about  400  meters  (1312  feet)  above  the  deepest  adit  (the  bottom 
of  the  valley),  while  the  other  was  on  the  7th  deep  level,  about 
60  meters  (196  feet)  below  the  said  adit.  The  former  of  these 
two  points  was  within  the  influence  of  the  ground-water. 

*  F.  Posepny,  "Die  Blei-und  Galmei-Erzlagerstatten  von  Eaibl."  Jahrb.  d. 
k.  k.  geol.,  E.  A.,  xviii.,  1873,  p.  372;  also  "  Ueber  die  Kohrenerze  von  Kaibl," 
Verhandl.  d.  k.  k.  g.  R.  A. ,  1873,  p.  54. 


70  THE    GENESIS    OF    ORE-DEPOSITS. 

Under  the  conditions,  decomposition  of  pyrite  and  zinc- 
blende  had  been  specially  great;  that  of  galena  less  so.  It  was 
often  possible  to  extract  from  the  dolomite  mass  the  stems  of 
galena  which  were  loose  in  it.  The  axis  of  such  a  stalactite- 
stem  (frequently  over  10  centimeters — 4  inches — long)  was 
often  an  open  space  through  which  one  could  blow  air,  whence 
the  name  "  pipe-ore "  given  to  this  surprising  occurrence. 
Specimens  not  decomposed  or  in  early  stages  of  alteration 
showed,  besides  galena,  crusts  of  pyrite  and  zinc-blende,  con- 
centrically disposed  around  the  axis. 

Figs.  25,  26,  27  and  28  (taken  from  my  former  treatise)  and 
representing  sections  of  individual  stalactites,  are  intended  to 
cover  the  variety  of  forms  in  these  occurrences.  Fig.  25  shows 
a  circular  stalactite  in  which  small  quantities  of  galena  may  be 
seen  in  the  pyrite  surrounding  the  axial  cavity.  The  outer 
crust  consists  of  thin  layers  of  wurtzite  (Schalenblende).  In  Fig. 
27  a  galena  mass  of  rhombic  section,  with  regular  striations  of 
secretion,  sits  immediately  on  the  side  of  the  cavity.  In  Fig. 
26  the  annular  mass  of  galena  is  surrounded  by  blende.  In 
Fig.  28  a  decomposed  body  of  blende  lies  within  the  galena 
mass,  which  latter  is  deposited  immediately  in  the  granular 
dolomite.  It  wrill  be  seen  that  the  crusts  upon  the  stalactites 
present  a  varying  order  of  succession,  and  that  the  stalactites 
have  fallen  from  the  roof  at  different  stages  of  their  growth. 

That  portion  of  the  ore-deposits  which  surrounds  the  locali- 
ties of  these  stalactites  has  an  entirely  normal  structure,  corre- 
sponding with  that  of  other  portions,  and  can  only  have  been 
formed  in  the  same  way,  namely,  from  ascending  mineral  solu- 
tions in  the  deep  region.  When,  under  such  circumstances,  a 
cavity  contains  stalactitic  deposits  instead  of  the  ordinary  wall- 
deposits,  that  particular  part  of  the  channel  must  have  been 
filled  with  gas.  The  decomposition  of  the  blende  is  due  here, 
as  in  Wiesloch,  to  the  subsequent  action  of  the  vadose  circu- 
lation. 

In  the  Matyas  Kiraly  mine  in  Yerespatak,  from  which  I  have 
already  described  the  envelopment  of  gold-aggregates  by  vari- 
ous metallic  carbonates  and  quartz,  there  has  been  found  also 
a  stalactitic  form  of  analogous  composition.  This  specimen  is 
in  my  possession,  but  there  are  two  others  in  the  National 
Museum  at  Budapest  which  practically  came  from  the  same 


THE    GENESIS    OF    ORE-DEPOSITS. 

mine.  One  of  the  latter  is  shown  in  Figs.  29  and  30,  and  my 
own  in  Fig.  31,  in  twice  the  natural  size.  The  latter  showed, 
after  being  broken  from  the  rock  in  which  it  occurred,  a  pro- 
jecting thread  of  gold;  and  in  polishing  the  surface  several 
annular  (and  hence  crystalline)  gold-aggregates  were  found  in 
the  axis  of  the  stalactite.  The  shaded  portion  indicates  the 
pink  manganese  crusts,  and  the  unshaded  portion  the  colorless 
carbonates.  The  outermost  crusts,  separated  here  and  there 
from  the  others  by  a  small  druse,  is  quartz. 

Wonderful  occurrences  of  this  kind  must  exist  in  the  Yalle 
mines  in  Missouri ;  but  we  have  only  mere  diagrams  of  them, 
which  do  not  exhibit  the  true  details  and  cannot  be  corrected 
with  the  aid  of  the  accompanying  text.  The  careful  objective 
representation  of  a  series  of  these  tubular  deposits  would  be  a 
service  to  science.  I  shall  recur  to  these  relations,  represented 
in  Figs.  32  to  35,  when  I  come  to  consider  the  Missouri  de- 
posits again. 

The  variety  of  the  occurrences  described  above  might  be  still 
further  illustrated ;  but  enough  has  been  said  to  furnish  from 
observation  the  elements  for  explaining  the  tilling  of  all  crus- 
tified  deposits.  When  the  elements  actually  found  in  such  de- 
posits are  taken  together  with  what  we  know  of  the  conditions 
of  underground  circulation,  no  competent  person  can  well  be- 
lieve in  any  other  origin  for  these  deposits  than  that  of  the  cir- 
culation we  have  described.  Whoever  has  followed  the  fore- 
going simple  statement  of  the  whole  chain  of  phenomena  will 
be  led  to  distinguish  sharply  between  the  effects  of  the  descend- 
ing vadose  and  those  of  the  ascending  profound  circulation,  and 
to  avoid  the  confusion  of  the  two  which  sometimes  character- 
izes the  discussion  of  the  subject. 

But  there  remains  a  serious  difficulty  in  determining  the 
genesis  of  non-crustified  deposits.  Here  the  indications,  by 
which  the  structure  and  gradual  growth  of  the  deposit  may  be 
traced,  are  at  first  lacking.  But  they  will  certainly  be  found 
by  patient  search ;  and  this  knowledge  must  be  furnished  by 
engineers  who  have  opportunity  to  study  the  phenomena  on 
the  spot  where  they  occur,  namely,  in  the  mine. 

The  non-crustified  deposits  consist,  however,  of  the  same 
minerals  as  the  crustified,  and  cannot  well  have  a  different 
origin ;  only  we  are  not  yet  in  a  position  to  offer  for  them 


72  THE    GENESIS    OF    ORE-DEPOSITS. 

similar  proofs  of  the  manner  of  their  formation.  Certainly 
they  also  are  the  products  of  ascending  mineral  solutions;  hut 
they  were  not  deposited  in  pre-existing  spaces,  and  conse- 
quently they  show  no  crustification.  In  describing  various  in- 
stances of  this  class,  I  shall  have  occasion  to  adduce  some  data 
bearing  upon  their  genetic  relations. 

But  even  the  crustified  deposits  need  to  be  further  illustrated 
by  examples,  especially  because  they  seldom  occur  in  nature  in 
pure,  unmixed  types.  We  ought  not  to  consider  ore-deposits 
without  reference  to  the  medium  which  contains  them ;  hence 
we  must  take  into  consideration  the  country-rock,  and  seek  to 
represent  the  analogies  of  nature  by  grouping  them  graphic- 
ally, as  it  were,  with  relation  to  two  axes,  representing  respec- 
tively the  genetic  class  and  the  country-rock.  "We  may  thus 
distinguish  the  following  general  groups  : 

Fillings  of  spaces  of  discission  (fissures,  etc.). 

Fillings  of  spaces  of  dissolution  in  soluble  rocks. 

Metamorphic  deposits  in  soluble  rocks ;  in  simple  sediments ; 
in  crystallines  and  eruptives. 

Hysteromorphous  deposits  (secondary  deposits,  due  to  sur- 
face agencies). 

PART  II. 

EXAMPLES  OF  CLASSES  OF  DEPOSITS. 

I  have  attempted  to  show  above  that  in  the  two  regions  of 
subterraneous  circulation  the  formation  of  ore-deposits  must 
have  taken  place  according  to  different,  almost  diametrically 
opposed  principles :  in  the  vadose  region  through  descension 
and  lateral  secretion,  and  in  the  profound  region  by  ascension, 
as  the  product  of  upward  currents.  I  have  pointed  out  that 
the  deepest  rocks  reached  by  mining  can  scarcely  be  the  origi- 
nal sources  of  the  metallic  solutions,  and  that  these  sources 
must  lie  at  still  greater  depths. 

That  is  to  say,  I  advocate  the  views  of  the  old  school,  and 
stand  opposed  to  the  assumptions  of  the  new  one,  lately  become 
popular,  which  does  not  need  to  go  to  inaccessible  depths  for 
the  source  of  the  metals,  but  professes  to  find  it  conveniently 
by  simple  chemical  tests,  without  the  necessity  of  leaving  the 
laboratory  and  searching  out  the  natural  deposits.  The  new 
doctrine  has  thus  far  failed  to  take  into  consideration  the  two 


THE    GENESIS    OF    ORE-DEPOSITS.  73 

different  underground  regions ;  and  we  may  expect  that  in  pro- 
portion as  it  comes  to  do  so,  its  conclusions  will  acquire  quite 
another  meaning. 

I  think  it  has  been  shown  that  the  deposits  of  the  deep  re- 
gion are  precipitates  from  ascending  springs.  It  remains  to 
inquire,  what  has  become  of  the  substances  which  were  not 
precipitated  in  such  channels,  but  reached  the  surface  in  solu- 
tion ?  Evidently  these  have  been  taken  up,  partly  by  the  sur- 
face circulation,  partly  by  the  vadose  underground  currents; 
and,  in  the  latter  case,  the  deposition  of  such  substances  in  the 
vadose  region  is  possible.  But  I  do  not  believe  that  we  are  as 
yet  in  a  position  to  form  a  correct  conception  of  the  process 
of  such  a  deposition ;  and  therefore  I  leave  this  question  open. 
Possibly,  many  impregnations,  for  which  we  can  trace  no  direct 
connection  with  ascending  springs,  yet  which  are  certainly  not 
idiogenous  (i.e.,  of  contemporaneous  origin  with  the  rock- 
matrix),  may  have  originated  in  this  way.  Possibly,  the  sul- 
phides which  occur  confined  to  the  neighborhood  of  organic 
remains  have  been  reduced  from  sulphates.  But  this  must  be 
confirmed  in  each  case  by  a  direct  study  of  the  facts,  and  not 
propounded  as  a  safe  generalization  for  all  cases. 

All  these  conclusions  are  based  upon  the  undoubtedly  cor- 
rect hypothesis  that  the  individual  minerals  of  the  deposits  are 
precipitates  from  aqueous  solutions.  The  important  part  played 
by  the  direct  products  of  the  barysphere — the  eruptive  rocks — 
is  not  ignored.  But  there  has  been  a  tendency  of  late  to  con- 
sider the  proof  of  any  solvents  as  superfluous,  and  apparently 
to  assume  that  certain  minerals  were  segregated  directly  from 
the  eruptive  magma.  With  respect  to  ferriferous  oxides,  this 
view  has  some  foundation;  but  the  notion,  apparently  held  in 
some  quarters,  that  sulphides  also  were  thus  segregated  from 
the  magma,  surpasses  my  comprehension.  It  is  true  that  pyrite 
is  sometimes  seen  upon  the  lavas  of  active  volcanoes ;  but  this 
occurs,  so  far  as  I  know,  only  when  fumaroles  and  solfataras 
emit  gases  and  vapors  which  decompose  the  rock,  and  there- 
fore the  agency  of  a  solvent  is  not  lacking.  I  am  therefore 
obliged  to  conclude  that  aqueous  solvents  are  the  chief  factor 
in  the  genesis  of  ore-deposits ;  and  I  shall  be  guided  by  this 
principle  in  the  following  illustrations  of  the  leading  genetic 
groups. 


74  THE  GENESIS  OF  ORE-DEPOSITS. 

1.  ORE-DEPOSITS  IN  SPACES  OF  DISCISSION. 

The  spaces  produced  in  rocks  by  mechanical  forces  are  pre- 
dominantly fissures ;  but  simple  forms  are  sometimes  rendered 
irregular  by  pre-existing  conditions,  such  as  those  of  stratifica- 
tion. Splitting  upon  a  bedding-plane,  coupled  with  a  simulta- 
neous longitudinal  movement  (such  as  gave  rise  to  the  ore- 
stock-works  which  the  Norwegian  miners  call  "  lineal ")  may 
produce  very  complicated  spaces,  which  must,  however,  be 
classed  as  spaces  of  discission. 

Every  fissure  is  the  consequence  of  a  tendency  to  dislocation 
transmitted  into  the  rock.  Hence  the  principal  effect  of  the 
process  is  the  production  of  the  dislocation,  not  that  of  the  fis- 
sure.* Where  yielding  stratified  rocks  are  exposed  to  such  a 
force,  they  first  bend  in  its  direction,  and  the  fracture  takes 
place  when  the  limit  of  elasticity  is  passed.  In  such  cases  it 
is  evident  that  the  movement  precedes  the  fracture.  Fig.  70, 
from  Rodna,  and  Fig.  69,  from  Raibl,  are  examples.  In  the 
latter,  the  gently  southward-dipping  contact  between  limestone 
and  slate  is  bent  and  faulted  by  a  IN",  and  S.  fissure.  At  Kis- 
banya,  in  Transylvania  (Fig.  99),  the  strata  of  gneiss  and  chlor- 
itic  slate,  striking  N".  and  S.,  are  so  bent  by  the  E.  and  "W. 
^Tagynyerges  vein  as  to  give  the  appearance  of  an  ore-bed. 

Although  the  fissures  produced  by  dislocating  forces  appear 
to  be  straight,  they  exhibit  (as  may  be  observed  where  veins 
have  been  traced  for  long  distances)  various  changes  of  direc- 
tion and  more  or  less  gradual  curves.  This  hinders  or  checks 
the  movement  of  one  convex  portion  upon  another,  and  pro- 
motes the  creation  of  open  spaces.  The  dislocating  force,  how- 
ever, continually  crowds  the  projecting  surfaces  together,  and 
thus  a  space  already  partly  filled  with  mineral  deposit  may  be 
closed,  or  an  open  space  may  be  filled  with  the  detritus  of  fric- 
tion. But  the  space  finally  left  open  facilitates  communication 
with  the  deep  region,  from  which  it  is  filled. 

According  to  this  conception,  the  vein-sheet  must  not  be  re- 
garded (as  is  too  often  done)  as  a  uniform  plate  of  ore.  On  the 
contrary,  it  consists  of  several  portions  of  very  unequal  value. 
The  most  valuable,  doubtless,  is  the  cavity-filling  which  forms 

*  F.  Posepny,  "Geol.  Betracht.  iiber  die  Gangspalten, "  Jahrb.  d.  k.  k.  Berga- 
kademien,  Vienna,  1874. 


THE    GENESIS    OF    ORE-DEPOSITS.  75 

the  bonanza  proper.  In  another  portion  the  mineral  solutions 
have  been  forced  to  penetrate  the  country-rock  and  impregnate 
it  with  ore.  A  third  portion  remained  altogether  impenetrable 
to  the  solutions,  and  represents  barren  ground.  These  three 
kinds  of  ground  may  evidently  show,  at  least  in  the  same  dis- 
trict, a  certain  regularity  of  relation ;  and  of  course  it  is  most 
important  to  determine  for  a  given  district  some  law  of  distri- 
bution of  the  rich  ore-bodies.  In  certain  instances  some  knowl- 
edge of  this  distribution  has  been,  in  fact,  successfully  acquired 
for  a  given  vein  before  it  had  been  exhausted  by  mining.  In 
many  other  cases  we  cannot  establish  the  law,  even  afterwards, 
because  the  most  necessary  records  were  not  made  during  the 
exploitation.  On  the  whole,  we  must  confess  that  our  knowl- 
edge of  the  laws  of  bonanzas  is  nothing  to  be  proud  of.  In 
this  respect  the  work  of  Professor  Moissenet  may  be  con- 
sulted.* 

Obviously,  in  all  such  investigations,  the  question  of  the 
origin  of  the  fissure  must  be  separated  from  that  of  its  filling. 
The  former  can  be  answered  only  upon  the  broad  basis  of  a 
knowledge  of  the  stratigraphic  relations  of  the  whole  vicinity, 
and  with  reference  chiefly  to  the  physical  properties  of  the 
rocks,  while  in  the  latter  their  chemical  properties  come  to  the 
front. 

As  a  rule,  however,  the  country-rock  of  an  ore-vein  is  more 
or  less  altered,  not  only  by  decomposition,  but  also  by  subse- 
quent solidification,  thus  rendering  much  more  difficult  the 
comparison  with  conditions  existing  far  from  the  vein.  This 
alteration  of  the  country-rock  is  universally  ascribed  to  the 
mineral  solutions  which  deposited  the  ore ;  and  it  is  not  im- 
probable that  a  close  study  of  it  might  enable  us  to  draw  con- 
clusions as  to  the  nature  of  these  solutions.  Unfortunately, 
petrography  is  still  confined  mainly  to  fresh,  typical  rocks,  and 
the  study  of  the  decomposed  country-rock  of  ore-veins  has  not 
been  cultivated  so  much  as  could  be  wished. 

All  veins  which  exhibit  friction-phenomena,  such  as  crushed 
country-rock,  slickonsides,  and  striations,  are  structurally  fault- 
fissures.  Such  a  vein  may  be  conceived,  therefore,  as  the 

*  M.  L.  Moissenet,  Etudes  sur  les  filons  de  Cornwall;  Parties  riches  des  filons ; 
Structure  de  ces  parties,  etc.,  Paris,  1874.  Engl.  tr.  by  J.  H.  Collins,  London, 
1877. 


76  THE    GENESIS    OF    ORE-DEPOSITS. 

boundary-surface  of  a  mass  which  has  undergone  movement. 
The  vein-phenomena  of  the  Hartz.  especially  support  this  con- 
ception. 

Some  vein-fissures  are  confined  to  a  given  rock,  and  do  not 
extend  into  the  adjacent  rock.  These  cannot  be  ascribed  to 
structural  dislocation,  but  must  rather  be  considered  as  caused 
by  changes  of  volume  in  the  immediate  formation.  They  are 
often  called  fissures  of  contraction.  The  most  striking  exam- 
ple which  I  have  encountered  is  shown  in  Fig.  36,  which  is 
from  the  gold-district  of  Beresov,  in  the  Ural  mountains.  Pa- 
Iseozoic  slates  are  there  traversed  by  a  number  of  granite  veins, 
20  to  40  meters  (66  to  131  feet)  thick,  and  striking  chiefly  K 
and  8. ;  and  each  of  these  granite  veins  is  again  traversed  by 
E.  and .  W.  gold-quartz  veins,  which  at  the  borders  of  the 
granite  either  become  barren  or  cease  altogether.  Near  the 
Beresov  is  the  Pysminsk  district,  in  which  the  granite  veins 
are  replaced  by  diorite  and  serpentine ;  but  strange  to  say,  the 
gold-quartz  veins  occupy  in  these  rocks  the  same  position  as 
in  the  peculiar  Beresov  granite,  locally  called  beresite.  Judg- 
ing from  Beresov  alone,  one  might  suspect  the  veins  to  have 
been  filled  from  the  granite ;  but  the  occurrence  in  Pysminsk 
suggests  caution. 

Finally,  the  veins  of  the  well-known  very  deep  mines  of  Przi- 
bram  might  be  ascribed  to  the  contraction  of  the  eruptive 
dikes  in  which  they  occur  (although  they  depart  here  and  there 
into  the  stratified  rocks);  but  we  cannot  dream  of  deriving 
their  metallic  filling  from  the  dikes.  The  Commission,  already 
mentioned,  established  to  test  the  applicability  of  the  lateral- 
secretion  theory  to  Przibram  conditions,  found  the  material  of 
the  dikes  to  be  the  same  in  depth  as  in  the  upper  zones.  The 
largest  amount  of  metallic  contents  attributed  to  the  diorite 
dikes  would  account  for  a  portion  only  of  the  thickness  of  ore 
in  the  veins.  The  greater  part  must  certainly  be  regarded 
as  of  deep  origin  ;  and  it  is  more  convenient  to  treat  the 
entire  metallic  contents  of  the  veins  as  derived  from  greater 
depths. 

Granting,  then,  that  the  vein-spaces  at  Beresov  were  formed 
by  the  contraction  of  the  granite  dikes,  the  vein-filling  must  be 
ascribed,  like  that  of  other  deposits,  to  metallic  solutions  as- 
cending from  the  deep  region. 


THE    GENESIS    OF    ORE-DEPOSITS.  77 

With  regard  to  structure,  the  fillings  of  ore-veins  very  often 
exhibit  distinct  crustification,  and  sometimes  even  a  symmetric 
succession  of  crusts  from  both  walls  to  the  central  druse.  But 
this  phenomenon  often  retires  into  the  background ;  crustifica- 
tion becomes  indistinct  or  disappears,  as  is  frequently  the  case 
in  gold-quartz  and  other  metamorphosed  veins,  in  which  its  last 
traces  appear  in  the  crystal-tips  of  the  central  druse  and  the 
occasional  indication  of  fibers  perpendicular  to  the  walls. 

Sometimes  one  part  of  a  vein  shows  distinctly  a  crustification 
which  in  other  parts  is  discerned  with  difficulty,  or  is  even 
wholly  absent.  Fig.  53  represents  a  specimen  from  the  Drei 
Prinzen  Spat  vein  in  the  eighth  level  of  the  Churprinz  Friedrich 
August  mine  at  Freiberg.  It  is  interesting  also  by  reason  of 
the  two  dislocations  which  it  exhibits.  The  oldest  vein  (a)  of 
quartz,  with  irregularly  disseminated  galena  and  zinc-blende, 
is  traversed  and  faulted  by  a  second,  very  clearly  crustified, 
vein,  the  filling  of  which  consists  of  hundreds  of  very  thin 
alternate  crusts  of  (6)  fluorite  and  quartz  and  (c)  barite,  sym- 
metrically arranged  on  both  sides,  with  a  central  druse  (d)  con- 
taining a  gray  earthy  mass.  A  quartz  seam  (ef)  then  faults 
both  veins.  The  manager  of  the  vein  assured  me  that  the 
specimen  occurred  in  the  vertical  position  in  wliich  I  sketched 
it.  (In  order  to  be  certain  at  all  times  on  this  important  point,  it 
is  advisable,  before  removing  a  specimen  from  its  natural  position, 
to  mark  it  in  color  with  a  vertical  arrow,  head  downward.) 

Very  often  the  crustification  of  a  vein-formed  ore-deposit  is 
only  to  be  traced  in  the  appearance  of  the  whole,  since  each 
of  many  irregular  veinlets  may  represent  separate  mineral 
crusts.  Accurate  pictures  of  such  occurrences  are  highly  in- 
structive, since  the  complications  are  often  so  great  that  the 
most  detailed  description  can  convey  no  correct  notion.  Figs. 
45  to  52,  by  reason  of  their  small  scale,  do  not  give  all  the 
details  contained  in  the  originals  from  which  they  are  taken. 
Figs.  45,  46,  and  47  are  from  Weisenbach's  famous  book,* 
and  represent  Freiberg  occurrences.  The  rest  are  from  Aus- 
trian publications. f  Figs.  48,  49,  and  50  refer  to  Przibram, 

*  Abbildung  merkw.  Gangverhaltn.  aus  d.  sacks.  Erzgebirge,  Leipzig,  1836. 

f  Auf  Befehl  s.  Exc.  Julius  Graf  en  Falkenhayn  herausgegebene  Silder  v.  d.  Lagerst. 
d.  Silber-u.  Bleibergb.  zu  Przibram,  etc.,  Vienna,  1887.  GeoL-bergmtinn  Karte  mil 
Profilen  u.  Ortsbildern  zu  Joachimsthal,  etc.,  Vienna,  1891. 


78  THE    GENESIS    OF    ORE-DEPOSITS. 

Figs.  51  and  52  to  Joachims  thai.  We  have  in  Fig.  47  a  speci- 
men, so  to  speak,  of  the  transition  from  a  vein  to  a  bedded 
deposit.  But  this  is  not  the  type  called  by  the  Germans  bed- 
vein  (Lagergang),  which  is  strictly  a  fissure-vein,  the  fissure 
of  which  coincides  with  the  plane  of  stratification  instead  of 
crossing  it.  Sometimes  it  is  a  joint  or  cleavage-plane  (often 
confounded  with  the  bedding)  which  the  bed-vein  occupies — a 
case  which,  I  believe,  I  have  found  at  Mitterberg,  in  Salzburg, 
and  at  the  Rammelsberg,  near  Goslar. 

In  this  category  belong  also  the  instances  of  a  squeezing  of 
strata  near  the  vein,  so  that  hanging-  or  foot-wall,  or  both,  show 
for  a  certain  distance  a  stratification  parallel  with  the  ore- 
deposit,  and  only  beyond  this  zone  does  the  normal  stratifica- 
tion in  a  different  plane  appear.  This  case  is  best  represented 
by  Fig.  99,  a  sketch  showing  an  E.  and  W.  vein  in  a  country 
of  slate  striking  !N".  and  S.  The  occurrences  atRodna  (Fig.  70) 
and  Raibl  (Fig.  69)  furnish  also  some  illustrations,  though  here 
it  is  chiefly  barren  fissures  which  traverse  and  bend  the  strati 
fication. 

The  text-books  usually  present  only  simple  outline-sketches 
of  such  conditions;  and  accurate  pictures  are  calculated  to 
surprise  those  who  have  not  been  much  in  mines,  by  exhibiting 
the  complications  of  the  actual  occurrences.  (Of  course,  com- 
plete objective  accuracy  would  require  photographs  of  polished 
surfaces.)  I  will  here  refer  only  to  one  of  the  most  complex 
pictures,  shown  in  Fig.  47  and  taken  from  Weissenbach's  col- 
lection (op.  cit.,  Plate  22).  The  Gabe  Gottes  vein  of  the  Bescheert 
Gliick  mine  at  Freiberg  consists  of  separate  masses  of  decom- 
posed gneiss,  bounded  by  barren  fissures,  and  the  stratification 
of  which  has  been  disarranged  by  their  mutual  pressure.  The 
fissures  have  no  filling,  but  the  gneiss  shows  filling,  nearly  rep- 
resenting its  stratification,  i.e.,  in  planes  almost  perpendicular 
to  the  walls  of  the  vein.  According  to  my  view,  the  vein 
being  in  this  place  split  up  into  small  fissures,  a  movement  must 
have  occurred,  probably  on  the  lowest  of  these  fissures  shown 
in  the  picture ;  but  the  result,  instead  of  being  an  ordinary 
fault,  was  a  pulling-apart  of  the  hanging-wall  strata,  which 
created  spaces  perpendicular  to  the  vein-plane,  and  approxi- 
mately between  the  strata.  These  spaces  were  subsequently 
filled  in  the  same  way  as  was  the  simple  main  fissure  itself  in 


THE    GENESIS    OF    ORE-DEPOSITS.  79 

other  parts  of  this  vein.     The  case  may  furnish  also  an  expla- 
nation for  certain  kinds  of  bed-veins. 

The  greater  number  of  ore-veins,  as  of  ore-deposits  in  gen- 
eral, occur  in  eruptive  rocks — a  circumstance  which  doubtless 
indicates  that  their  metallic  contents  have  been  derived,  directly 
or  indirectly,  through  these  or  other  media,  from  the  bary- 
sphere.  The  most  productive  ore-veins  are  wholly  in  such 
rocks,  but  others  occur  in  stratified  rocks,  traversed  by  erup- 
tives.  Comparatively  few  occur  wholly  in  stratified  rocks.  In 
such  cases  large  faults  have  unquestionably  opened  communi- 
cation with  the  barysphere.  To  emphasize  these  relations,  I 
will  bring  forward  some  illustrations  from  well-known  ore-vein 
districts  comprising  such  occurrences : 

a.  In  stratified  rocks,  entirely  unconnected  with  eruptives; 

b.  In  the  neighborhood  of  eruptive  masses,  and  partially  en- 
closed therein ; 

c.  Wholly  within  large  eruptive  formations. 

a.    Ore- Veins  in  Stratified  Rocks. 

Genuine  ore-veins  entirely  unconnected  with  eruptive  rocks 
are  not  easily  to  be  found — especially  not  in.  cases  of  important 
and  well-studied  districts.  Clausthal,.  in  the  Hartz,  still  comes 
nearest  to  fulfilling  these  conditions.  The  Hartz  range  is  a 
mass  of  folded  palaeozoic  strata,  which  lifts  itself,  in  lenticular 
form,  above  the  North  German  plateau  of  mainly  Mesozoic 
rocks.  The  strata  comprising  the  Hartz  generally  strike  at 
right-angles  to  the  W.  ~N.  W.  direction  of  the  axis  of  the  range, 
but  most  of  the  faults  are  approximately  parallel  to  this  axis, 
so  that  the  terms  "  axial "  and  "  cross  "  mean  here  the  opposite 
of  what  they  would  mean  in  ranges,  the  main  axes  of  which 
coincide  with  the  strike  of  the  strata. 

Clausthal. — The  ore-veins  of  Clausthal  are  somewhat  pecu- 
liar. There  are  zones  of  altered  rocks,  20  to  80  meters  (66  to 
262  feet)  wide  and  extending  as  far  as  about  15  km.  (9  miles), 
in  which  the  ore-bodies  are  somewhat  irregularly  distributed. 
These  rock-zones  are  called  vein-clay-slates  (Gangthonschiefer), 
to  distinguish  them  from  the  ordinary  slates  (Culmschiefer)  of 
the  district;  and  recent  careful  investigations  have  shown  that 
their  composition  practically  corresponds  with  that  of  the  latter. 
They  are  therefore  in  fact  country-rock,  altered  for  the  most 


80  THE    GENESIS    OF    ORE-DEPOSITS. 

part  mechanically,  and  only  to  a  slight  extent  chemically. 
They  are  foliated ;  but  the  foliation  rather  parallels  the  planes 
of  movement,  being  somewhat  steep,  while  the  strata  of  the 
surrounding  region  have  generally  but  a  slight  dip.  These 
zones  may  therefore  be  best  conceived  as  the  result  of  the 
friction  of  the  great  masses  which  have  here  been  rubbed  to- 
gether. 

In  recent  times,  chiefly  by  A.  von  Groddeck,  it  has  been 
actually  proved  that  these  zones  represent  great  faults,  along 
which  either  the  foot-wall  mass  was  moved  S.  W.  downward,  or 
the  hanging-wall  was  lifted  IS".  E.  The  vertical  movement, 
measured  at  certain  points,  would  be  about  400  meters  (1312 
feet) ;  but  it  is  probable  that  the  movement  of  one  mass  upon 
the  other  did  not  follow  the  true  dip,  and  that  the  horizontal 
component  wras  much  greater  than  the  vertical.  The  faulted 
portions  of  a  kersantite  vein  discovered  by  Groddeck  show 
that  each  southern  mass  was  moved  further  west,  or  each 
northern  mass  further  east. 

The  network  in  these  zones  of  dislocation  is  also  peculiar. 
As  indicated  in  Fig.  37,  lenticular  masses  have  been  isolated, 
after  undergoing  severally  a  movement  in  the  direction  of  the 
axis  of  the  Hartz  range ;  so  that  the  whole  zone  of  lenticular 
masses  expresses  the  displacement  which  the  solid  crust  has 
experienced.  The  structural  significance  of  the  zones  is  thus 
clearly  disclosed,  as  a  means  of  communication  with  a  deep  re- 
gion from  which  the  mineral  solutions  ascended,  to  deposit 
ores  in  the  fissures  of  dislocation.  As  I  have  already  remarked, 
an  ore-vein  is  thus  represented  as  the  boundary  of  a  displaced 
rock-mass,  and  so  is  brought  into  direct  structural  relation  with 
the  country-.rock. 

A  glance  at  the  geological  map  of  the  Hartz  Mountains  will 
show,  however,  that  even  this  region  is  not  free  from  eruptive 
rocks ;  for  the  stratified  formations  crossing  the  mountain  axis 
are  traversed  by  masses  of  granite,  which  have  evidently  played 
a  part  in  the  building-up  of  the  range  above  the  plateau. 
Moreover,  according  to  the  investigations  of  Dr.  K.  A.  Lossen,* 
and  others,  contact-metamorphosis  of  the  stratified  rocks  has 

*  "Geol.  u.  petrogr.  Beitrage  zur  Kenntniss  des  Harzes,"  Jahrb.  der  k.  preuss. 
geol.  Landesanstalt  il.  Bergak.  fur  1881,  p.  47. 


THE    GENESIS    OF    ORE-DEPOSITS.  81 

proceeded  from  them.  E.  Kayser*  fixes  the  elevation  of  the 
granite  between  the  end  of  the  Carboniferous  and  the  begin- 
ning of  the  Permian,  and  since  several  of  the  faults  extend  into 
this  rock,  he  thinks  it  cannot  have  been  a  factor  in  the  fissure- 
formation.  Lessen,  on  the  other  hand,  is  inclined  to  ascribe 
to  the  granite  an  active  part  in  the  formation  of  the  ore-deposits, 
and  (if  I  understand  him  correctly)  to  believe  that  these  deposits 
were  influenced  by  their  position  against  the  granite  nucleus 
of  the  Hartz  Mountains,  which  is  said  to  lie  steep  on  one  side 
and  more  flat  on  the  other,  beneath  the  sedimentary  strata. 

Accurate  geological  surveys  of  the  Hartz  have  noted  a  large 
number  of  fault-fissures,  some  of  which  connect  the  two  great 
ore-deposits  of  Clausthal  and  Andreasberg.  Those  which  are 
called  Euscheln  resemble  the  dislocation  zones  of  Clausthal. 
They  are  fissures,  up  to  30  meters  (98  feet)  wide,  approxi- 
mately parallel  with  the  mountain-axis,  and  filled  with  a  clayey 
or  fragmentary  material,  full  of  striations  and  slickensides,  and 
generally  of  dark  color. 

Andreasberg. — Roughly  parallel  with  these  Huscheln  run  the 
silver-ore  veins  of  Andreasberg,  which  carry  ore  only  on  one 
side  of  the  Ruscheln,  and  lose  their  ore  when  they  approach  the 
latter.  It  was  formerly  imagined  that  the  two  main  JRuscheln 
enclosed  a  lenticular  mass  of  the  country,  to  which  the  silver- 
ores  were  confined ;  and  H.  Crednerf  still  expresses  this  view. 
But  Kayser  (op.  cit.,  p  443)  observes  that  the  mines  have  dis- 
closed a  convergence  of  the  Euscheln  to  the  west  only,  and  that 
a  similar  convergence  to  the  east  has  been  purely  assumed  from 
analogy,  whereas  the  surface-indications  are  rather  those  of  a 
wider  separation  in  that  direction.  (See  Fig.  38.) 

We  have  here  a  case  in  which  the  ores  occupy,  not,  as  in 
Clausthal,  a  previously  prepared  zone  of  dislocation,  but  a  net- 
work of  veins.  H.  Credner  has  pointed  out  that  the  mineral 
solutions  were  unable  to  penetrate  the  walls  of  the  dislocation- 
zones,  and  conceived  in  this  connection  that  these  walls  en- 
closed a  lenticular  body  of  rock.  But  the  main  question  con- 
cerns the  origin  of  the  more  recent  network  of  fissures.  We 

*  "Ueber  d.  Spaltensystem  am  S.  W.  Abhang  des  Brockenmassivs,"  etc., 
Ibid.,  p.  452. 

f  "Geogn.  Beschreib.  d.  Bergw.  distrikts  von.  Andreasberg,"  Zeitsch.  d.deutsch 
geol.  GeselL,  xvii.,  p.  221. 


82  THE    GENESIS    OF    ORE-DEPOSITS. 

must  assume  that  when  the  dislocation-zones  were  formed,  the 
mineral  solutions  had  no  opportunity  to  enter  them,  because 
(as  was  the  case  in  many  great  faults,  e.g.,  those  of  Przibram) 
no  spaces  of  discission  were  formed.  Afterwards,  however,  a 
second  system  of  fissures  originated,  adjusting  itself  to  the  con- 
ditions created  by  the  first,  and  producing  rock-fragments,  the 
relatively  slight  movement  of  which  did  not  fill  the  interstitial 
spaces  with  the  detritus  of  friction. 

But  outside  of  the  angle  between  the  'Ruscheln,  there  are  also 
veins,  which,  considering  their  direction,  may  be  continuations 
of  the  silver-veins  inside,  although,  being  differently  filled,  they 
are  not  so  regarded. 

It  was  formerly  attempted  to  connect  two  eruptive  rocks  with 
the  formation  of  these  ore-veins  :  the  granite  which  appears  to 
the  north,  beyond  the  fault-fissures;  and  the  diabase  which 
touches  them  at  many  points  to  the  south.  The  latter,  how- 
ever, is  now  considered  to  be  a  stratified  layer  in  the  series  of 
the  country.  Both  rocks  have  been  passive  in  the  formation 
and  the  filling  of  the  fissures,  and  we  must  look  again  to  the 
deep  region  as  the  source  of  the  ores. 

b.  Ore-  Veins  in  the  Neighborhood  of  Eruptive  Masses. 

The  Erzgebirge. — It  would  be  impossible  here  to  pass  in  re- 
view the  innumerable  veins  of  the  Erzgebirge  in  Saxony  and 
Bohemia.  Such  a  review  will  soon  be  furnished  by  the  publi- 
cation of  a  work  on  this  subject  by  the  eminent  Saxon  mining 
geologist,  H.  Miiller  (who  has  received  the  honorary  title  of 
"  Gangmiiller,"  to  distinguish  him  from  the  many  other  Miil- 
lers  of  Germany).  In  this  region,  veins  in  the  greatest  variety 
occur  in  gneiss,  with  here  and  there  an  eruptive  dike ;  but  the 
latter  can  scarcely  be  considered  as  more  than  indications  of  a 
former  communication  with  the  barysphere. 

Besides  different  porphyries  and  diorites,  there  is  an  occa- 
sional dike  of  basalt.  At  Joachimsthal,  in  Bohemia,  we  can 
recognize  pre-  and  post-basaltic  ore-deposition.  We  find  here, 
as  in  many  other  districts,  two  vein-systems  at  right  angles ; 
one  striking  N.-S.,  and  accompanied  with  porphyry  dikes;  the 
other  striking  E.-W.,  and  accompanied  with  dikes  of  basalt 
and  (according  to  recent  views)  phonolite.  The  E.-W.  fissures 
are  occupied  partly  by  basaltic  dikes,  partly  by  ore-veins  which 


THE    GENESIS    OF    OKE-DEPOSITS.  83 

were  deposited,  some  before  and  some  after  the  basalt,  a  satis- 
factory proof  that  the  fissures  were  formed  at  the  period  of 
basaltic  eruption.  How  far  the  basalt  took  part  in  the  ore-de- 
position, however,  has  not  yet  been  shown. 

In  the  basaltic  and  "  basalt-wacke  "  dikes  of  this  district,  at 
the  considerable  depth  of  some  300  meters  (984  feet)  below  the 
surface,  petrified  tree-trunks  were  found,  a  fact  which  fur- 
nishes an  analogy  to  the  reported  discoveries  in  the  Bassick 
mine  in  Colorado. 

Przibram. — An  entirely  different  picture  is  presented  by 
Przibram  in  central  Bohemia,  where  we  encounter  not  only  a 
great  structural  fault,  but  also  eruptive  dikes,  which  are  fol- 
lowed by  most  of  the  ore-veins. 

In  central  Bohemia  the  general  strike  is  NE.-SW.  for  all 
rocks  except  the  diorite  dikes,  which  strike  N.-S.,  thus  vary- 
ing 45°  from  the  prevailing  direction.  Above  the  granite  lies 
first  a  formation  of  pre-Cambrian  slates ;  upon  this  follows  un- 
conformably  the  Cambrian  system,  consisting  below  of  con- 
glomerates and  sandstones,  and  above  of  fossiliferous  slates. 
Sections  across  the  strike  show  repetitions  of  the  pre-Cambrian 
and  Cambrian  strata  due  to  great  faults,  which  likewise  strike 
KE.-SW.  (Fig.  40). 

The  one  main  fault  which  has  been  exposed  by  mining  to 
the  depth  of  1110  meters  (3600  feet)  is  properly  a  so-called 
Wechsel,  by  which  the  older  stratum  (in  the  hanging-wall  of 
the  fault)  has  been  slid  over  the  later  stratum  (in  the  foot- wall). 
Several  other  faults,  similar  in  character,  though  not  explored 
on  an  equal  scale,  occur  in  the  district ;  and  it  may  be  imagined 
that  before  this  shoving  together  of  the  Palaeozoic  strata  of 
central  Bohemia  they  must  have  occupied  a  much  larger  area 
than  at  present. 

This  main  fault,  called  the  " LettenUuft"  is  constituted  by  a 
zone  of  clay  and  crushed  rock,  from  2  to  10  meters  (6.5  to  33 
feet)  wide.  At  Przibram  itself,  the  sandstones  which  contain 
the  ore  are  succeeded  in  the  hanging-wall  side  by  pre-Cambrian 
slates.  A  little  further  SW.,  at  Bohutin,  granite  appears  on 
the  hanging-wall  of  the  Lettenkluft — evidently,  as  the  cross- 
section  indicates,  the  granite  foundation,  here  outcropping  a 
second  time,  of  the  whole  Palaeozoic  series. 

Numerous  N.-S.  dikes  occur,  and  in  the  ore-bearing  zone 

6 


84  THE    GENESIS    OF    ORE-DEPOSITS. 

they  are  so  close  together  that  some  cross-sections  show  them 
to  constitute  almost  one-third  of  the  total  rock-mass.  The  ore- 
veins  are  mostly  in  these  diorite  dikes.  Only  occasionally  do 
they  enter  the  stratified  rocks,  returning  soon  to  the  dikes  they 
have  left,  or  to  others  of  the  group.  In  dip  also  they  mainly 
follow  the  dikes,  so  that  we  may  here  assert  with  confidence 
that  the  already  existing  dikes  determined  the  formation  of  the 
ore-hearing  vein-fissures. 

As  already  narrated  in  Part  I.,  this  district  was  made  a  test 
of  Sandberger's  lateral-secretion  theory.  Careful  and  repeated 
analysis  showed  the  presence  of  metals  in  the  rocks,  but  could 
not  decide  the  question  whether  these  metals  were  primitive 
ingredients  or  secondary  impregnations.  Since  such  metallic 
traces  occur  in  both  the  eruptive  and  the  sedimentary  rocks, 
but  cannot  possibly  be  in  both  cases  primitive,  it  is  probable 
that  they  are  in  both  cases  secondary.  There  is  then  in  this 
case,  notwithstanding  the  connection  of  the  ore-veins  with  the 
dikes,  no  proof  that  they  were  formed  by  the  leaching  of  the 
country-rock.  If  the  vein-material  (as  is  very  likely)  was  de- 
rived from  eruptive  rocks,  these  were  situated  much  deeper 
than  the  eruptive  rock  disclosed  down  to  1110  meters  (3640 
feet)  below  the  surface,  or  500  meters  (1640  feet)  below  sea- 
level. 

The  Cambrian  sandstone  basin  of  Przibram  is  unsymmetri- 
cal ;  one  side  dips  gently  northwest,  the  other  (next  to  the  fault) 
slightly  southeast.  In  the  latter  part,  which  is  also  more  highly 
metamorphosed,  lies  the  bonanza  or  rich  ore-ground,  which 
therefore  starts  from  the  intersection  of  the  great  structural  fault 
with  the  zone  of  eruptive  rocks,  in  other  words,  from  the  point 
relatively  nearest  to  the  barysphere. 

In  the  steeply-dipping  sandstone  series,  certain  strata  are 
petrographically  characteristic ;  and  when  these  are  traced  to 
the  intersecting  dikes,  it  becomes  clear  that  the  latter  (and 
hence  the  ore-veins  also),  are  fissure-faults.  Thus  Fig.  39,  a 
section  through  the  Franz  Joseph  shaft,  shows  dislocations  of 
the  strata  (adinole-beds)  as  great  as  about  200  meters  (656 
feet). 

It  should  be  added  that  the  dikes  present  different  kinds  of 
eruptive  rock,  and  that  they  are  generally  decomposed  in  the 
neighborhood  of  the  ore-veins — a  result  naturally  to  be  attrib- 


THE    GENESIS    OF    ORE-DEPOSITS.  85 

uted  to  the  action  of  the  mineral  springs ;  also,  that  stratified 
rocks  show,  near  the  granites,  a  contact-metamorphosis  which 
has  converted  them  into  hornstone.  This  phenomenon  recalls 
the  Hartz,  especially  the  St.  Andreasberg  district. 

c.  Ore-  Veins  Wholly  Within  Large  Eruptive  Formations. 

Hungary. — If  we  turn  to  Hungary,  we  find  many  veins 
wholly  included  in  eruptive  rocks.  One  of  the  best  known 
districts  is  that  of  Schemnitz,  which  presents  in  geological  con- 
ditions the  nearest  analogue  of  the  Washoe  district  and  the 
Comstock  lode  in  Nevada. 

In  both  cases,  various  eruptives,  principally  Tertiary,  such  as 
diorite,  andesite,  trachyte  and  rhyolite,  ranging  to  basalt,  are 
spread  over  a  Mesozoic  (mainly  Triassic)  foundation.  The  "N. 
and  S.  extension  of  these  masses  and  of  the  ore-veins  they  con- 
tain is  alike  in  both  districts.  The  number  of  veins  at  Schem- 
nitz is  very  large,  and  they  exhibit  a  very  great  variety  of  fill- 
ing. In  some  of  them,  so-called  "  ore-columns,"  i.e.,  specially 
rich  ore-channels  (chimneys  or  shoots),  have  been  recognized. 
Those  in  the  Griiner  vein,  according  to  M.  Y.  Lipold,*  are 
short  horizontally,  but  much  prolonged  in  the  direction  of 
their  pitch,  obliquely  on  the  dip  of  the  vein.  In  other  ore- 
veins,  e.g.,  in  the  Spitaler  master-lode,  which  is  about  40  meters 
(131  feet)  wide,  and  has  been  traced  for  8  km.  (5  m.) ;  also  in 
the  Bieber  and  other  veins,  the  ore-bodies  are  said  to  have 
covered  large  areas  of  the  vein-sheet.  The  ore  richest  in  gold 
is  reported  to  be  the  so-called  Zinnopel,  a  crust  consisting  of 
jasper,  with  pyrite,  chalcopyrite  and  galena,  which  surrounds 
fragments  of  an  earlier  quartz  crust. 

In  the  trachyte  range  of  Yihorlat  Grutin,  which  runs  !N"W. 
and  SE.,  approximately  parallel  with  the  Hungarian  boundary, 
there  is  a  series  of  gold  and  silver  mining  districts,  containing 
occasional  large  veins  with  numerous  small  ones.  Among  the 
former  are  those  of  Nagybanya  and  Felsobanya,  where  several 
domes  of  trachyte  or  of  andesite,  breaking  through  the  late 
Tertiary  "Qongerien"  strata,  are  in  turn  traversed  by  large 
veins,  which  split  up  near  their  outcrops,  so  as  to  exhibit  in 
vertical  cross-section  a  fan-shaped  arrangement. 

*  "  Der  Bergbau  von  Schemnitz  in  Ungarn,"  Jahrb.  d.  k.  k.  geol.  E.  AnstalL, 
1867,  p.  403. 


86  THE    GENESIS    OF    ORE-DEPOSITS. 

Further  east  is  the  Kapnik  mining  district,  containing  a 
series  of  separate  veins ;  then  comes  Rota,  similar  in  character ; 
and  finally  (over  the  line  in  Transylvania),  the  district  of 
Olahlaposbanya,  the  veins  of  which  are  partly  in  the  eruptive 
rock,  partly  in  the  old  Tertiary  strata  which  it  traverses. 

Throughout  the  range,  silver-ores  predominate,  occasionally 
with  a  considerable  gold-value.  In  the  eastern  portion,  copper- 
ores  appear. 

The  Dacian  Gold-Field. — In  southwestern  Transylvania,  in 
the  Dacian  gold-district,  all  the  gold-mines  are  grouped  in  con- 
nection with  four  separate  eruptive  zones  of  recent  origin. 
The  main  rock  of  the  region  is  Cretaceous  sandstone,  with  oc- 
casional exposures  of  Jurassic  and  Triassic  strata,  the  latter  of 
which  include  heavy  outflows  of  melaphyre,  and  also  masses 
of  crystalline  rocks.  The  recent  eruptives,  comprising  por- 
phyry, diorite,  andesite,  basalt,  etc.,  occur  in  a  triangle,  the 
base  of  which  is  formed  by  the  widest  range,  the  Cietrasian, 
which  strikes  N~W.  and  SE.,  and  in  which  are  the  mines  of 
Nagyag,  Magura,  Fiizesd,  Boiza  and  Ruda.  In  a  second,  ap- 
proximately parallel  range,  are  the  mines  of  Faczebaja  and 
Almas;  in  a  third,  those  of  Yulkoj  and  Verespatak;  and  in 
a  fourth,  forming  the  apex  of  the  triangle,  those  of  OfFen- 
banya.* 

These  mines,  which  are  for  the  most  part  very  ancient  (pre- 
Roman),  I  shall  treat  fully  in  a  monograph  now  in  course  of 
preparation.  In  the  whole  Dacian  gold-district  the  predomi- 
nant deposits  are  fissure-veins,  sometimes  represented  by  mere 
"  knife-blade  "  seams,  continuous  for  short  distances  only.  In 
some  places,  as  in  the  celebrated  Yerespatak  district,  other 
types  of  deposit  are  represented,  the  ores  of  which,  however, 
also  occur  in  spaces  of  discission,  namely,  in  eruptive  breccias, 
between  the  related  fragments,  in  the  form  which  I  have  else- 
where called  typhonic  masses ;  but  these  are  ore-bearing  only 
where  they  are  in  contact  with  the  ore-veins.  The  same  is 
true  of  the  conglomerates  into  which  these  breccias  sometimes 
pass,  and  in  which  the  ore  takes  the  place  of  the  interstitial 
cement,  as  I  have  explained  in  a  preceding  chapter,  and  illus- 

*  F.  Posepny,  "Allgem.  Bildd.  Erzfiihrung  im  Siebenb.  Golddistrikte, "  Jahrb. 
d.  k.  k.  geol.  E.  Anstalt.,  xviii.,  p.  297. 


THE    GENESIS    OF    ORE-DEPOSITS.  87 

trated  in  Fig.  18.  For  further  elucidation,  I  show  in  Fig.  41 
a  breccia,  and  in  Fig.  42  a  conglomerate.  (It  should  be  ob- 
served that  the  mutual  relation  of  the  fragments  of  a  breccia 
can  be  recognized  only  when  they  have  not  suffered  much 
movement  after  fracture.)  In  both  these  specimens,  the  rock 
is  quartz-porphyry  with  quartz-crystals  of  pea-size.  In  Fig.  41 
the  interior  of  the  fragments  is  considerably  decomposed, 
whereas  the  exterior  shows  a  thin  layer,  either  of  undecom- 
posed  rock,  or  of  material  subsequently  impregnated  with 
silica  from  the  open  interstices,  and  thus  made  capable  of  re- 
sistance. Sometimes  the  porphyry  is  found  to  be  traversed 
by  a  complex  network  of  fissures,  filled  (except  as  to  some 
wider  spaces  of  intersection)  with  a  clastic  mass,  like  sand- 
stone. The  interstices  of  the  conglomerate,  Fig.  42  (ex- 
cept the  spaces  containing  crusts  of  manganese  spar  and 
quartz),  are  filled  with  a  clastic  cement,  mostly  silicified  into 
hornstone. 

This  sort  of  ore-filling  is  comparable  in  some  degree  with 
ore-deposits  in  soluble  rocks,  when  the  filling  has  passed  from 
the  space  of  discission  proper  into  the  rock,  after  room  has 
been  made  for  it  in  the  latter  by  dissolution.  In  the  cases  be- 
fore us  such  room  was  made  by  the  partial  washing  away  of 
the  (probably  clayey)  cement  of  the  breccias  and  conglom- 
erates. 

Verespalak. — The  gold-district  of  Yerespatak  is  situated  at 
the  north  end  of  the  second  eruptive  range.  The  two  por- 
phyry masses  of  Kirnik  and  Boi  form  a  center,  around  which 
sandstone  and  porphyry-tufa  lie  almost  horizontally,  and  in 
part  unconformably,  upon  folded  Cretaceous  sandstones  below. 
The  whole  district  is  surrounded  by  a  zone  of  trachytes,  an- 
desites,  and  their  lavas,  which  once  (as  may  be  inferred  from 
the  fragments  remaining  on  the  porphyry  and  tufa)  overspread 
the  entire  district,  and  have  been  removed  by  erosion,  laying 
bare  the  two  older  eruptive  masses  of  the  porphyry. 

A  funnel-shaped  depression  seems  to  have  been  formed  in 
the  folded  Cretaceous  strata,  from  the  middle  of  which  as- 
cended the  porphyry-outflows,  furnishing  also  the  material  for 
the  porphyry-tufa,  which  fills  this  funnel-shaped  basin. 

The  principal  gold-bearing  rock  is  the  porphyry,  yet  the 
tufas  and  the  Cretaceous  rocks  near  the  porphyry-outflow  carry 


88  THE    GENESIS    OF    ORE-DEPOSITS. 

gold ;  whereas,  no  gold  or  ore  of  any  kind  occurs  in  the  tra- 
chytic  and  aiidesitic  lavas  which  once  covered  the  region. 

Vulkoj. — At  Vulkoj,  however,  at  the  southern  end  of  the 
second  eruptive  range,  almost  the  opposite  is  the  case.  Here 
the  older  and  deeper  quartzose  rock  carries  little  ore,  while 
gold  abounds  in  the  overlying  andesites.  Several  mines  of  the 
Dacian  gold-district  have  encountered  in  depth  the  stratified 
rocks  through  which  the  eruptives  came,  and  the  result  has 
generally  been  disastrous  to  the  miner,  the  ore-veins  having 
either  ceased  entirely  or  become  pinched  to  barren  fissures. 
In  the  first  case  it  would  appear  that  the  vein-fissures  had  been 
formed  by  the  contraction  of  the  eruptive  material.  But,  in 
general,  it  should  be  said  that  these  phenomena  are  by  no 
means  clearly  and  reliably  reported.  The  prejudices  of  the 
miners  play  too  large  a  part  in  their  reports.  This  much  is 
certain,  that  any  fissure,  in  passing  from  one  rock  to  another, 
is  likely  to  exhibit  a  certain  irregularity  in  both  direction  and 
filling,  and  that  a  change  of  this  kind  should  not  be  allowed 
to  discourage  at  once  all  further  exploration. 

In  some  cases  there  has  been  found,  below  an  eruptive  rock 
containing  ore- veins,  a  decomposed  breccia  of  the  same,  which 
was  quite  barren.  The  great  porphyry  mass  of  Kirnik,  at 
Verespatak,  has  been  pierced  through  and  through  with  ancient 
and  modern  workings,  like  the  pores  in  a  sponge.  In  recent 
years  deep  adits  have  been  driven  into  it  to  reach  fresh  ground, 
but  with  unsatisfactory  results.  A  short  time  ago  the  deepest 
of  these  adits  encountered  in  the  nucleus  of  the  Kirnik  mass, 
not  the  ore-bearing  porphyry,  but  decomposed  clastic  rock  and 
porphyry-breccia,  which  may  be  supposed  to  be  the  filling  of 
the  crater-opening.  The  Yulkoj  mass,  which  has  been  almost 
cut  into  two  halves  by  very  ancient  open-workings  along  its 
crest,  contained  a  series  of  N.-S.  veins,  the  richest  of  which 
(the  Jeruga)  was  cut  in  depth  by  adits  from  both  sides.  On 
the  south  side  appears  a  slaty  Cretaceous  rock,  underlying  the 
porphyry,  and  extending  (see  Fig.  43)  upon  the  Jeruga  plane, 
with  two  offsets,  to  the  deepest  adit  on  the  north  side,  where  it 
strikes  the  decomposed  breccias,  in  which  the  very  rich  ores 
mined  above  can  no  longer  be  found  to  continue. 

As  to  the  continuation  of  the  veins  in  the  slaty  rock,  the 
following  facts  are  pertinent.  West  of  the  Vulkoj  mass,  in  the 


THE    GENESIS    OF    ORE-DEPOSITS.  89 

sandstones  and  slates,  there  is  another  gold-field,  that  of  Botesiu, 
the  veins  of  which  are  analogous,  both  in  strike  and  in  ore- 
filling,  to  those  of  Vulkoj.  Botesiu  shows  no  eruptive  rocks; 
nevertheless,  a  study  of  the  whole  region  shows  that  the  forma- 
tion of  its  vein-fissures  must  have  been  connected  with  them, 
and  it  is  even  not  impossible  that  they  may  once  have  extended 
as  far  as  this,  and  may  have  been  removed  by  subsequent  ero- 
sion. It  follows  that  we  must  assume  the  Yulkoj  veins  to  ex- 
tend below  the  andesite  into  the  slate,  though  this  has  been 
doubted  by  some.  Fig.  44  shows  the  situation  in  an  E.-W. 
section. 

In  the  region  of  Boitza  the  eruptive  zone  (predominantly 
of  quartzose  dacites  or  porphyries)  crosses  an  exposure  of  Meso- 
zoic  limestones  and  melaphyrs,  and  the  veins  pass  directly  from 
the  porphyry  into  the  underlying  melaphyr. 

At  Nagyag,  Magura,  and  Fiizesd,  in  following  the  gold-veins 
in  depth,  masses  of  Tertiary  sandstones  and  conglomerates  are 
formed,  broken  through  and  enveloped  by  the  eruptive  rocks. 

At  four  places  in  the  Dacian  gold-district,  namely,  Offen- 
banya,  Faczebaja,  Fericiel  and  Nagyag,  telluric  ores  occur.  In 
the  neighborhood  of  Zalatna  there  is  cinnabar,  and  at  several 
points  near  Korosbanya  there  are  copper-ores  carrying  a  little 
gold.  Gold  is,  however,  mainly  connected,  as  has  been  ob- 
served, with  the  four  ranges  of  Tertiary  eruptives,  and  appears 
chiefly  in  these  rocks,  though  also  in  the  stratified  rocks  which 
they  traverse. 

The  occurrence  of  gold  in  this  case  is  thus  somehow  related 
to  the  eruptions ;  but  since  I  have  never  found  it  as  a  primitive 
or  idiogenous  constituent  of  these  rocks,  I  do  not  believe  that 
it  was  derived  originally  from  them.  There  is,  therefore, 
nothing  left  but  to  consider  the  eruptions  as  the  agents  of  a 
communication  with  the  deep  region,  from  which  at  these 
points  the  mineral  springs  ascended.  The  Dacian  gold-district 
will  furnish,  upon  further  exploration,  important  contributions 
to  the  inquiry  into  the  original  source  of  the  gold.  For  in- 
stance, if  the  auriferous  character  of  the  veins  of  Yulkoj  should 
be  found  to  continue  in  the  shaly  sandstones  underlying  the 
andesite,  my  view  would  be  confirmed. 

The  Comstock  Lode. — The  most  thoroughly  studied  Ameri- 
can vein-phenomena  bearing  on  this  question  are  doubtless 


90  THE    GENESIS    OF    ORE-DEPOSITS. 

those  of  the  Comstock  lode.  It  is  not  necessary  to  enter  here 
upon  a  detailed  description.  I  content  myself  with  a  reference 
to  the  three  large  treatises  upon  the  district,*  of  which  Becker 
especially  discusses  the  genetic  question.  To  appreciate  this 
question,  however,  some  simple  illustrations  are  required ;  and 
these  have  been  compressed  into  Figs.  58  to  63. 

As  already  observed,  the  general  geological  conditions  of  the 
Comstock  lode  show  a  strong  analogy  to  those  of  the  Schem- 
nitz  district.  Only  occasional  bodies  of  sedimentary  rocks  are 
found,  while  the  principal  mass  of  the  whole  elevated  region 
consists  of  a  great  variety  of  eruptive  rocks,  principally  of  the 
more  recent  periods.  The  altitudes  of  the  more  important 
points  above  sea-level  are  about  as  follows : 

Meters.  Feet. 

Mount  Davidson  (the  highest  point  of  the  re- 
gion),        .        .         .        .        .        .        .  2420  7941 

Outcrop  at  the  Gould  and   Curry  mine  (the 

datum-line  for   measurements   of    depth),  1950  6400 

The  Sutro  Tunnel,  at  different  points,  1840  to  f  1390  4560 

1865  feet  below  datum-line,        ...  I  1382  4535 

The  deepest  point  in  the  Belcher  and  Crown 

Point  shaft,  3414  feet  below  datum,   .        V,  910  2986 

These  figures  alone  indicate  the  immense  extent  of  the 
eruptive  material. 

The  stratified  rocks  occur  in  a  considerable  continuous  body 
at  Gold  Hill,  in  the  southern  part  of  the  district,  while  in  the 
northern  part  only  a  small  body  enclosed  in  eruptive  rocks  is 
found  in  the  Sierra  Nevada  shaft. 

The  several  eruptive  rocks  have  been  differently  defined  at 
different  times,  according  to  the  changes  in  petrography  and 
in  the  methods  of  investigation  pursued.  Becker  distinguishes  : 
1.  Basalt  (B).  2.  Later  hornblende-andesite  (LHA).  3.  Augite- 
andesite  (AA).  4.  Earlier  hornblende-andesite  (EHA).  5. 
Later  diabase  or  black  dike  (LDb).  6.  Earlier  diabase  (EDb). 
7.  Quartz-porphyries  (QP).  8.  Metamorphosed  diorites  (MDr). 
9.  Porphyritic  diorites  (PDr).  10.  Granular  diorites  (GDr). 

*  Clarence  King,  U.  S.  Geol.  Explr.  of  the  40th  Parallel,  iii.,  Mining  Industry, 
Washington,  1870. 

J.  A.  Church,  The  Comstock  Lode :  Its  Formation  and  History,  New  York,  1879. 

G.  F.  Becker,  "Geology  of  the  Comstock  Lode,"  etc.  —  U.  S.  Geol.  Survey 
Monograph,  Washington,  1882. 


THE    GENESIS    OF    ORE-DEPOSITS.  91 

11.  Metamorphic  rocks  (M).  12.  Granites  (G).  This  classi- 
fication is  based  upon  careful  microscopic  examination.* 

The  two  principal  veins  (the  Comstock  and  the  Occidental) 
strike  K-S.,  and  the  Comstock  has  been  traced  5  or  7  km.  (3 
or  4  m.),  according  as  its  branches  are  omitted  or  included  in 
the  measurement.  The  position  and  the  branching  of  the 
veins  are  shown  in  the  sketch-map,  Fig.  58,  in  which  the  two 
most  important  eruptive  rocks,  the  diorite  and  the  diabase,  are 
emphasized  by  shading,  the  others  being  indicated  by  letters, 
as  in  the  above  list,  The  diorite  forms  the  foot-wall  from  Gold 
Hill  to  Virginia  City.  South  of  Gold  Hill  metamorphic  slates 
form  the  foot-wall,  and  even  extend  across  in  part  to  the  hang- 
ing-wall side,  as  does  the  diorite  to  the  north  of  Virginia  City. 
Moreover,  in  one  place  a  dike  of  diabase — the  so-called  "  black 
dike," — occurs  immediately  on  the  foot-wall. 

The  hanging-wall  is  principally  diabase,  at  least  in  depth. 
In  the  upper  region  it  is  sometimes  covered  with  other  erup- 
tives,  most  frequently  with  hornblende-andesite. 

On  the  whole  (with  variations  at  some  places),  the  Comstock 
presents  wide,  gently-dipping  masses,  predominantly  of  crushed 
and  decomposed  country-rock,  and  enclosing  large  flat  "horses" 
of  the  same.  The  filling  is,  as  a  rule,  saccharoidal  granular  quartz 
(sometimes  more  compact),  in  which  the  ores  are  very  finely 
disseminated.  At  some  points  they  have  occurred  concentrated, 
forming  the  bonanzas  to  which  the  colossal  gold-  and  silver- 
production  of  the  district  is  due.  The  ores  are  silver-ores 
(stephanite,  polybasite,  argentite),  with  sometimes  galena  and 
zinc-blende.  The  bullion  produced  from  them  contains  about 
half  its  value,  or  6  to  7  per  cent,  of  its  weight,  in  gold. 

Some  of  these  bonanzas  were  in  the  upper  region  and  came 
to  the  surface.  Others  (like  the  richest  one  of  all,  in  the  Con- 
solidated Virginia  and  California  mine)  were  found  in  the 
deep  region  ;  and  it  is  asserted  that  they  were  limited  on  all 
sides,  without  connection  with  other  ore-bodies.  This  would 

*  Messrs.  Arnold  Hague  and  J.  P.  Iddings  (Bull.  17,  U.  S.  Geol.  S.,  1885, 
"On  the  Development  of  Crystallization  in  the  Igneous  Kocksof  Washoe,"  etc.) 
have  stated  as  their  conclusion  that  GDr,  EDb  and  AA  are  identical ;  PDr.  is 
EHA  ;  MDr  is  LHA ;  and  LDb  is  B  ;  apparent  differences  being  due  to  con- 
ditions of  cooling.  In  Bull.  No.  6,  Gal.  Acad.  of  Sc.,  1886,  Mr.  Becker,  after  a 
reinvestigation  of  the  locality,  denies  this  conclusion  in  toto,  so  far  as  the  Corn- 
stock  rocks  are  concerned. 


92  THE    GENESIS    OF    ORE-DEPOSITS. 

make  them  unlike  our  ore-channels  or  chimneys,  which  usually 
do  have  interconnection.  But  I  cannot  conceive  of  their  forma- 
tion in  any  other  way  than  upon  the  hypothesis  that  in  such 
places  more  open  spaces  existed,  through  which  larger  quanti- 
ties of  dilute  metallic  solutions  passed  and  made  deposits. 

The  distribution  of  the  bonanza-areas  upon  the  vein-area  is 
quite  irregular ;  and  it  has  not  been  possible  hitherto  to  trace 
any  connection  between  the  bonanzas  and  the  petrographic  or 
structural  conditions  in  their  vicinity.  In  form  they  are 
equally  without  any  law,  as  far  as  has  yet  been  observed.  The 
bonanzas  of  the  Con.  Ya.  and  Cal.  consisted  of  a  main  body 
and  three  lenticular  masses  higher  up,  which,  taken  together, 
have  a  flat  pitch  to  the  north.  The  bonanza  between  Belcher 
and  Yellow  Jacket,  on  the  other  hand,  followed  the  true  dip 
of  the  vein;  while  the  bonanza  in  Justice — a  mine  on  the 
NW.-SE.  branch,  which  dips  KE.  much  less  steeply  than  the 
main  lode — shows  again  a  north  pitch. 

This  NW.-SE.  branch  of  the  Comstock  shows  a- filling  dif- 
ferent in  some  respects  from  that  of  the  main  lode,  and  may 
be  considered  as  a  cross-vein,  running  into  the  Oomstock,  or 
into  the  black  dike  which  accompanies  its  foot-wall.  (Becker's 
atlas,  ix.) 

In  the  Justice  mine,  namely,  the  filling  is  mostly  calcite,  with 
little  quartz,  instead  of  quartz  with  very  subordinate  calcite,  as 
in  the  main  lode.  According  to  Becker  (1.  <?.,  p.  219)  the  calcitic 
filling  is  characteristic  of  the  whole  SE.  branch.  According  to 
Church  (op.  cit.,  173),  compact  crusts  of  calcite  alternate  in  the 
Justice  mine  with  their  quartz  crusts.  This  is  the  only  clear 
report  of  crustification  anywhere  on  the  Comstock.  (I  be- 
lieve, however,  that  I  was  able  to  observe  upon  a  rich  speci- 
men from  the  Con.  Va.  bonanza,  after  polishing,  a  parallel 
structure  in  the  mineral  aggregate.  I  received  this  specimen 
in  1876  from  Mr.  Fair,  one  of  the  "  bonanza  kings,"  as  a  sort 
of  compensation  for  the  refusal  to  permit  me  to  enter  the  then 
rich  mine !) 

A  comparison  of  the  many  cross-sections  of  the  Comstock 
published  by  King,  Church  and  Becker,  and  representing,  of 
course,  various  stages  of  knowledge  of  the  vein,  shows  that  no 
normal  or  average  section  can  be  given,  because  the  condition 
at  different  points  on  the  strike  are  so  different,  and  at  some 


THE    GENESIS    OF    ORE-DEPOSITS.  93 

places,  e.g.  the  junctions  of  the  branches,  developments  have 
not  given  satisfactorily  complete  exposures.  The  sections,  Figs. 
59  to  63,  are  given  (on  a  scale  too  small  to  show  much)  merely 
to  illustrate  the  distribution  of  the  country-rocks.  They  are 
reduced  from  Becker's  monograph.  In  the  three  northerly 
sections  the  foot-wall  is  granular  diorite ;  in  the  two  southern 
(Yellow  Jacket  and  Belcher),  and  along  the  SE.  branch,  it  is 
metamorphic  slate.  In  the  southern  portion,  the  so-called 
black  dike  (according  to  Becker,  later  diabase)  appears  on  the 
foot-wall,  and  follows  the  vein  beyond  the  point  where  the  SE. 
branch  leaves  it.  The  hanging-wall  is  diabase,  except  at  the 
northern  end,  where  diorite  becomes  the  hanging-wall  as  well 
as  the  foot-wall.  In  the  upper  region,  however,  earlier  diabase 
is  covered  by  other  eruptives.  Diabase  is  the  hanging-wall  of 
the  SE.  branch  also ;  but  in  the  foot-wall  of  that  branch,  besides 
the  metamorphous  slates,  granular  diorite  and  quartz-porphyry 
appear. 

So  far  as  the  sources  of  the  eruptive  rocks  can  be  inferred, 
they  were  all  (except  that  of  the  diorite)  on  the  hanging-wall 
side  of  the  vein,  as  were  also  the  mineral  springs  which  sub- 
sequently decomposed  these  rocks.  But  the  ascending  thermal 
waters  encountered  in  these  mines  were  within  the  vein  itself; 
whence  it  may  be  concluded  that  the  ore-bearing  solutions 
came  by  that  road  from  the  deep  region,  and  not,  according  to 
the  lateral-secretion  theory,  from  the  side.  In  other  words,  the 
Comstock  ores  were  not  washed  from  those  rocks  which  have 
been  mined  between  1950  and  910  meters  (7941  and  2986 
feet)  above  sea-level,  but  from  material  lying  much  deeper. 

The  investigations  of  Gr.  F.  Becker  were  made  at  a  time  when 
importance  was  still  attached  to  Sandberger's  theory,  and  the 
correctness  of  his  method  of  inquiry  was  assumed.  The  mat- 
ter takes  a  different  aspect  when  we  (quite  justifiably)  doubt 
whether  the  minute  metallic  admixtures  detected  by  wet  or 
dry  analysis  were  originally  in  the  rock,  and  acknowledge  that 
they  may  possibly  have  entered  it  afterwards.  This  is  evi- 
dently the  case  with  the  precious  metals  in  the  pyrite  of  the 
ore-bearing  rock.  That  this  pyrite  is  a  secondary  impregna- 
tion can  be  proved  with  the  microscope,  and  is  admitted  by 
Becker  also.  In  my  opinion,  any  eruptive  rock  may  give  rise 
by  metamorphosis  to  the  type  which  we  call,  in  Hungary, 


94  THE    GENESIS    OF    ORE-DEPOSITS. 

greenstone,  greenstone-trachyte,  etc.,  and  which  F.  von  Richt- 
hofen  named  propylite,  because  of  its  frequent  occurrence  as 
the  country-rock  of  ore-deposits.  Whether  the  precious  metals 
can  be  detected  in  this  rock  depends  wholly  upon  its  impregna- 
tion, or  that  of  one  of  its  constituent  minerals,  with  pyrite. 
But  it  does  not  follow  that  this  was  the  primitive  condition. 
From  this  standpoint  are  to  be  regarded  the  metallic  values 
reported  by  Becker,  and  here  reduced,  for  the  sake  of  better 
understanding,  from  cents  per  ton  to  grammes  per  1000  kilo- 
grams. A  pyrite  washed  from  decomposed  diabase,  near  the 
face  of  the  north  branch  of  the  Sutro  tunnel,  contained  3  cents 
silver -and  8  cents  gold,  i.e.,  0.72  grm.  silver  and  0.12  grm.  gold, 
per  metric  ton.  The  pyrite  from  the  slates  in  the  Belcher 
mine  carried  even  18  c.  (4.32  grm.)  silver  and  20  c.  (0.30  grm.) 
gold.  Fresh  diabase  is  said  to  have  contained  4  to  5  c.  (0.6  to 
0.7  grm.)  gold;  the  diorite  of  Bullion  ravine,  only  a  trace; 
while  the  andesite  yielded  about  as  much  as  the  diabase. 
Augite  separated  by  Thoulet's  method  from  the  diabase  was 
found  to  be  eight  times  as  rich  as  a  corresponding  quantity  of 
the  feldspar. 

Comparative  investigations  are  reported  to  have  shown  that 
the  decomposed  diabase  contains  only  half  as  much  silver  as 
the  fresh — a  circumstance  which  was  interpreted  in  favor  of  the 
lateral-secretion  theory,  on  the  assumption  that  the  decomposed 
diabase  had  given  up  half  its  silver  to  the  vein-filling. 

Since  the  diorite  in  the  upper  portion  of  Bullion  ravine 
shows  only  traces  of  silver,  but  at  the  mouth  of  the  ravine,  near 
the  vein,  contains  a  considerable  amount,  Becker  considers  this 
indicative  rather  of  an  impregnation  of  the  rock  proceeding 
from  the  vein. 

Moreover,  the  andesites  and  quartz-porphyries  also  contain 
small  amounts  of  silver;  while  the  strongly  calcareous  meta- 
morphic  diorite  carries  8  c.  (1.92  grms.)  per  ton,  which  might 
be  connected  with  the  vein-filling  in  the  Justice  mine.  Finally, 
the  basalt  contains  nearly  as  much  silver  as  the  older  diabase ; 
but  the  basalt  cannot  be  cited  as  a  source,  because  it  comprises 
the  freshest  rock  in  the  district,  and  shows  no  trace  of  decom- 
position in  its  olivine  (Becker,  I.  c.,  pp.  223-225).  These  facts 
would  be  favorable  to  the  notion  of  lateral  secretion,  if  only  it 
could  be  proved  at  the  same  time  that  the  metalliferous  char- 


THE    GENESIS    OF    ORE-DEPOSITS.  95 

acter  was  primitive.  But  our  knowledge  does  not  go  so  far  as 
that;  and  the  Comstock,  like  the  deep  mines  of  Przibram, 
ceases,  therefore,  to  be  a  proof  of  the  lateral-secretion  theory. 
The  Comstock  differs  in  many  respects  from  typical  ore- 
veins.  It  is  properly  a  quartz-vein,  in  which,  at  various  points, 
important  ore-concentrations  have  been  formed,  not  showing 
(except  in  the  Justice  mine)  any  clear  crustifieation,  though  this 
may  have  been  present  at  some  time,  and  may  have  been  ob- 
literated by  metamorphosis  of  the  vein-mass,  e.g.,  through  the 
replacement  of  calcite  by  quartz.  It  is  also,  in  the  main,  a 
contact-vein,  between  a  diorite  foot-  and  a  diabase  hanging-wall, 
with  steep  spurs  running  upward  into  the  diabase  and  travers- 
ing also  still  more  recent  eruptives.*  Some  of  these  peculiar- 
ities are  represented  in  other  districts. 

2.  ORE-DEPOSITS  IN  SOLUBLE  ROCKS. 

In  this  group  we  shall  find  two  genetic  types  represented  : 
the  fillings  of  spaces  of  dissolution,  and  the  metasomatic  de- 
posits, the  origin  of  which  will  be  particularly  considered,  to- 
gether with  some  related  metamorphic  deposits  in  soluble 
rocks,  which  have  not  yet  been  sufficiently  studied  to  be  classed 
apart, 

The  expression  "  soluble  rock  "  is  to  be  understood  in  its  or- 
dinary sense  of  solubility  in  the  waters  commonly  represented 
on  the  earth's  surface.  Acid  and  caustic  waters  will  attack, 
more  or  less,  nearly  all  rocks,  though  not  so  as  to  dissolve  them 
completely,  as  we  see  limestone  dissolved.  I  include  especially 
among  the  soluble  rocks,  rock-salt,  gypsum,  limestone,  and 
dolomite.  Of  the  following  instances  I  shall  describe  most 
fully  those  which  I  have  personally  studied,  giving  only  the 
essential  outlines  of  other  related  occurrences. 

Eodna. — The  ore-deposit  of  Rodna,  in  NE.  Transylvania,  is 
interesting  to  me  (apart  from  analogies  which  it  offers  with 
Leadville,  Colo.),  as  the  first  in  which  I  had  the  opportunity  to 
study  the  origin  of  an  ore-deposit  by  replacement. 

It  is  situated  on  the  line  of  two  andesite  ranges,  having  a 
common  strike, — the  Hungarian  Vihorlat  Gutine,  stretching 

*  This  is  denied  by  Hague  and  Iddings,  op.  cit.,  p.  41. — See  foot-note  on  p.  91 
of  this  paper. 


96  THE    GENESIS    OF    ORE-DEPOSITS. 


,  and  the  Transylvanian  Hargitta  range,  running  SE.,  — 
and  at  the  point  where  this  line  cuts  through  the  mass  of  the 
Rodna  Alps.  The  predominant  rock  is  mica-slate,  with  numer- 
ous intercalations  of  limestone,  and  is  traversed  by  many  dikes 
and  masses  of  andesite.  Ore-deposits  have  been  found  at  many 
points  in  the  district.  The  most  important,  situated  in  the 
Benyes  mountain,  was  carefully  studied  by  me  in  1862,  after 
the  ore-bodies  in  the  mine  had  been  worked  out.  J.  Grimm 
had  examined  the  mine  in  1834,  and  had  considered  the 
deposits  to  be  primitive  beds  at  the  contact  between  lime- 
stone and  mica  slate,  and  to  have  occupied  that  position  be- 
fore the  andesite  eruption,  by  which  they  had  been  much 
shattered. 

The  ores  (pyrites,  black  zinc-blende,  and  argentiferous  galena, 
slightly  auriferous,  with  quartz  and  calcite)  often  occurred,  it  is 
true,  on  the  gently-dipping  contact-planes;  but  in  certain  E. 
and  "W.  lines  they  stood  steeply,  much  like  veins.  In  these 
places  the  flat  deposit,  and  with  it  the  stratification,  had  sud- 
denly turned  upward,  and  it  was  clear  to  me  that  the  occurrence 
represented  a  peculiar  form  of  fault,  namely,  a  bending  of  the 
strata,  followed  by  fracture  in  the  direction  of  the  dislocating 
force,  when  the  limit  of  cohesion  had  been  passed.  Here  and 
there,  in  these  steep  places,  the  stopes  had  been  carried  beyond 
the  contact,  and  the  resulting  appearance  was  as  if  the  steep 
deposit  had  been  the  primary  one,  and  had  supplied  the  ore  to 
the  contact.  Occasionally  eruptive  breccias  were  observed 
along  the  steep  deposits.  At  lower  levels,  in  the  downward 
continuation  of  the  fissure  of  the  steep  deposit,  eruptive  rocks 
and  thin  breccias  occurred  ;  and  these  became  predominant  in 
the  lowest  part  of  the  mine. 

The  structure  of  the  ore-beds  was  mainly  massive,  and  not 
crustified.  In  some  places,  however,  druses  had  been  devel- 
oped, which  showed  the  same  paragenetic  succession  as  the 
mass  of  the  bed,  and  which  contained  pseudomorphs  of  pyrite 
and  galena  after  calcite.  The  thickness  of  the  ore-bed  was  ex- 
tremely variable,  the  greater  part  of  the  contact-area  being 
scarcely  worth  working,  while  at  single  points  colossal  masses 
of  ore  were  found.  These  circumstances  led  me  to  consider 
the  deposits,  not  as  contemporaneous  in  origin  with  the  rock, 
but  as  subsequently  formed  by  the  circulation  of  mineral  waters 


THE    GENESIS    OF    ORE-DEPOSITS.  97 

along  the  contact-planes.  In  other  respects  I  adopted  at  that 
time  the  explanation  of  J.  Grimm.* 

Mining  was  then  active  chiefly  on  the  north  slope  of  the 
Benyes  divide  ;  and  the  sedimentary  rocks  were  cut  off  towards 
the  south  by  andesite.  I  pointed  out  that  on  the  south  slope, 
beyond  the  andesite,  there  were  various  ancient  mines,  and  rec- 
ommended that  they  be  explored  in  depth,  by  means  of  an  adit. 
This  led  to  the  discovery  of  several  deposits,  which  gave  new 
life  to  the  industry.  After  cutting  through  the  andesite,  the 
explorers  found  steep  deposits  at  the  contact  of  andesite  and 
limestone,  and,  in  the  limestone,  near  its  contact  with  the  mica- 
slate,  a  flat  deposit,  which,  being  above  the  ground-water  level, 
had  been  transformed  into  carbonate  of  lead. 

The  somewhat  complicated  conditions  are  shown  in  Fig.  70, 
as  far  as  this  can  be  done  in  a  single  section.  The  deposit  at 
the  contact  of  andesite  and  limestone  indicates  at  once  a  genetic 
connection  with  the  eruptive  rock,  and  renders  it  probable  that 
the  ore-beds  also  are  due  to  the  after-effects  of  the  eruption. 
Even  on  the  north  slope  there  were  some  reasons  for  this  con- 
clusion. For  instance,  at  the  ore-bodies  locally  called  Thon- 
strassen,  ores  occurred  in  the  midst  of  eruptive  breccia,  which 
could  not  be  taken  for  fragments  of  the  orignal  bed.  Baron 
Constantine  von  Beustf  found  traces  of  "  ring-ores,"  indicating 
a  formation  in  open  cavities. 

In  seeking  an  explanation  of  all  the  facts,  I  was  led  to  give 
up  the  view  of  J.  Grimm, J  which  he,  however,  still  maintained, 
citing  Offenbanya  as  another  instance  in  which  a  pre-existing 
deposit  on  the  contact  between  limestone  and  mica-slate  had 
been  shattered  by  an  andesite-eruption.  But  in  that  instance, 
also,  I  had  the  opportunity  to  satisfy  myself  that  the  then  ac- 
cessible mine-workings  showed  no  fragments  of  an  earlier  ore- 
deposit,  but  only  ore-formations  under  the  influence  of  the 
andesite. 

Grimm  had  had  in  mind  the  deposits  of  Rodna  and  Offen- 

*  Some  results  of  my  studies  at  Kodna  will  be  found  in  the  Verhandlungen  d.  k. 
k.  g.  R.  Anstalt.,  1865,  pp.  71,  163, 183,  and  1870,  p.  19. 

f  "  Berne rkungen  uber  d.  Erzvorkommen  von  Rodna,"  Verh.  d.  k.  k.  geol.  R. 
A.,  1869,  p.  367. 

I  J.  Grimm,  "  Zur  Kenntniss  der  Erzvorkommen  von  Rodna,  "Fer^.  d.  k.  k. 
geol.  R.  A.,  1869,  p.  367  ;  and  F.  Posepny,  "Die  Natur  der  Erzlagerstatten  von 
Rodna,"  iWd.,  1870,  p.  19. 


98  THE    GENESIS    OF    ORE-DEPOSITS. 

banya  when  he  established,  under  the  first  division  in  his  sys- 
tematic classification,*  the  second  sub-division,  "  Occurrences 
of  Ores  as  Fragments  of  Earlier  Deposits,  in  Breccias,"  etc. 

Offenbdnya. — Offenbanya,  in  the  Transylvania  gold  district, 
has  various  deposits  analogous  to  those  of  Rodna,  and  also 
veins,  with  telluride  ores.  We  are  here  interested  in  its  mass- 
deposits,  at  the  contact  of  limestone  and  andesite,  one  of  which 
is  illustrated  in  Fig.  71. 

Beneath  the  limestone  widely  extending  through  the  district, 
mining  has  disclosed  a  mica-slate  (the  so-called  underground 
slate) ;  and  at  the  contact  of  the  two  a  flat,  pyritous  deposit. 
The  whole  stratified  series  is  traversed  by  andesite ;  but  near 
its  contact  with  the  limestone  a  steep,  rich  mass-deposit  extends 
from  the  surface  down  to  the  mica-slate.  This  deposit  is  highly 
crustified,  and  was  evidently  formed  in  a  pre-existing  space. 

The  flat  deposit  shows  no  crustification,  and  may  have  been 
formed  by  metasomatic  replacement  of  the  lime  at  the  contact 
between  the  impermeable  and  the  soluble  rock.  The  analogy 
with  the  conditions  on  the  south  slope  of  the  Benyes  mine,  at 
Rodna,  is  evident,  though  I  do  not  know  whether  at  Rodna  the 
flat  deposit  has  been  followed  as  yet  to  its  junction  writh  the 
steep  one.f 

Rezbdnya. — Rezbanya  in  SE.  Hungary  represents  different 
conditions.  Here,  in  an  indistinctly  stratified  Mesozoic  lime- 
stone, occur  long  spaces  filled  with  ore,  descending  steeply  and 
irregularly  in  shape  like  that  of  the  cavity  produced  by  pour- 
ing a  stream  of  warm  water  upon  a  snow-bank.  This  extreme 
case  is  of  great  theoretical  interest,  although  such  ore-bodies 
having  but  one  considerable  dimension,  and  that  in  the  most 
unfavorable  direction  for  mining,  mainly  downward,  are  not 
attractive  from  a  commercial  standpoint.  I  visited  Rezbanya 
first  in  1868,  and  published  some  observations  concerning  it, 
which  may  have  contributed  to  induce  the  Hungarian  govern- 
ment to  take  up  the  subject  later,  and  intrust  to  me  a  more 
thorough  investigation.  I  will  here  mention  only  some  things, 

*  Die  Lagerstdtten  der  nutzbaren  Mineralien,  Prague,  1869,  p.  32. 

t  At  the  time  of  the  visit  of  G.  vom  Eath,  in  1878  (described  by  him  in  the 
Zeitschr.  d.  d.  geol.  Gesellsch.,  xxx.,  1878,  p.  556),  this  ore-body,  28  meters  (92 
feet)  thick,  had  been  developed  for  a  height  of  85  meters  (280  feet)  and  a  length 
of  120  meters  (394  feet)  without  reaching  its  termination. 


THE    GENESIS    OF    ORE-DEPOSITS.  99 

interesting  from  the  genetic  standpoint,  and  refer  for  details  to 
my  published  monograph  upon  the  subject.* 

In  the  Rezbanya  region,  lying  above  clay  slates  and  Permian 
and  Liassic  sandstones,  appear  numerous  isolated  bodies  of 
limestone,  indicated  by  their  fossils  to  be  of  various  ages,  from 
the  Lias  to  the  Neocomian,  seldom  distinctly  stratified,  and, 
when  they  are  traversed  by  eruptive  rocks,  often  showing  a 
crystalline  structure.  The  ore-filling  is  mostly  confined  to  the 
neighborhood  of  the  eruptives,  and  sometimes  to  the  contact, 
where  garnet-rock  occurs  as  a  well-known  product  of  local 
metamorphosis.  Since  my  examination,  there  may  have  been, 
in  this  region,  many  interesting  and  scientifically  important  de- 
velopments, which  are  unfortunately  unknown  to  me.  On  the 
basis  of  my  old  notes  only,  I  shall  confine  myself  to  the  de- 
scription of  a  single  district,  cut  off  from  commercial  commu- 
nication, that  of  Yalle  Sacca.  The  name  is  that  of  the  valley, 
which  heads  in  a  high  mountain  range  of  Permian  and  Liassic 
sandstones,  and  after  a  short  course  ends  in  a  wild  limestone 
canon,  leading  into  the  Galbina  valley.  The  sides  of  Valle 
Sacca  consist  chiefly  of  limestone,  which  is  traversed  by  a  num- 
ber of  eruptive  dikes  and  one  larger  mass  of  a  syenitic  char- 
acter. Fig.  64  gives  a  somewhat  generalized  section  of  the 
!N"W.  slope  of  the  valley  and  district  on  the  line  of  the  so-called 
fourth  adit.  At  the  adit-mouth  is  cut  the  syenite  mass,  which 
extends  also  to  the  opposite  slope;  and  the  adjoining  portion 
of  the  limestone  has  been  metamorphosed  to  a  crystalline  mass, 
while  the  limestone  further  SW.  is  for  the  most  part  still  com- 
pact. On  the  west  side,  the  limestone  adjoins  sandstone  along 
a  !N".— S.  line,  which  doubtless  represents  a  large  fault.  Approx- 
imately parallel  to  it  run  the  greenstone  dikes,  which,  though 
they  seem  to  be  mutually  parallel,  in  reality  intersect  one  an- 
other at  very  acute  angles,  thus  constituting  a  highly  elongated 
net-work.  The  dikes  are  not  alike.  Most  of  them  may  be 
considered  aphanitic  or  dioritic;  one,  however,  is  quartz-por- 
phyry, with  dihexahedra  of  quartz,  of  pea-size. 

The  principal  deposit  is  the  so-called  Reichenstein  stock, 
which  had  been  worked,  during  the  period  prior  to  my  visit, 
to  a  depth  of  about  400  meters  (1300  feet),  from  its  outcrop, 

*  Geologisch-montanistische  Studie  der  Erzlagerstdtten  von  Rezbdnya,  Budapest,  1874. 

7 


100  THE    GENESIS    OF    ORE-DEPOSITS. 

340  meters  above  the  deepest  adit,  to  a  level  60  meters  below 
the  adit.  Fig.  65  shows  the  form  of  the  ore-channel  on  the 
strike.  The  horizontal  section  of  the  body  was  most  frequently 
circular  or  elliptical.  In  some  places  one  dimension  strongly 
predominated,  so  as  to  give  the  appearance  of  a  fissure-filling. 
At  the  outcrop,  according  to  the  old  maps,  there  was  but  one 
channel.  Below,  this  divided  into  neighboring  and  mutually 
connected  branches.  Several  of  these  might  continue  parallel 
and  independent  for  considerable  distances.  The  total  sectional 
area  of  the  channels  averaged  perhaps  20  to  30  square  meters 
(215  to  322  square  feet) ;  but  at  some  levels  the  deposit  was  only 
present  in  traces,  whereas  at  others  it  had  many  times  its  aver- 
age section.  Fig.  66  shows,  by  the  difference  between  the 
plumb-line  and  the  arrow,  the  angle  between  the  true  dip  and 
the  pitch  of  the  ore-body,  oblique  to  it. 

The  ores  were  doubtless  sulphides  originally,  but  were  after- 
wards oxidized  in  places.  Rich  silver-ores  predominated,  espe- 
cially argentite,  pieces  of  which  weighing  several  pounds  ap- 
pear to  have  been  no  rarity.  Besides  this  mineral  there  were 
hessite  (telluride  of  silver),  tetrahedrite,  redruthite,  galena,  bis- 
muthinite,  and  various  pyrites.  Taking  these  together  with 
the  oxidized  ores,  the  deposit  represented  a  whole  mineral 
cabinet.  The  maximum  silver-value  was  reported  as  12  to  20 
kilos  per  1000  (1.2  to  2  per  cent),  the  gold  being  3  grammes 
to  each  kilo  of  silver.  The  percentage  of  lead  was  about 
twenty  times,  and  that  of  copper  about  ten  times,  as  great  as 
of  silver.  The  metric  ton  (2206  pounds)  would  yield,  at  this 
rate,  24  to  40  per  cent,  of  lead,  12  to  20  per  cent,  of  copper,  12 
to  20  kilos  (386  to  643  ounces  Troy)  of  silver,  and  36  to  60 
grammes  (1.15  to  1.83  ounces  Troy)  of  gold.  The  deposit  was 
therefore  a  bonanza  in  the  American  sense.  In  fact,  it  yielded 
from  $100  to  $150  per  ton. 

Although  I  could  not  see  this  deposit  in  process  of  extrac- 
tion, I  was  able  to  conclude  positively,  from  specimens  of  the 
ore  and  from  the  analogy  of  similar  deposits  in  the  district, 
that  it  had  been  formed  by  the  precipitation  of  successive 
crusts. 

As  regarded  the  origin  of  the  cavity,  I  was  at  first  influenced 
in  my  views  by  the  numerous  caves  of  the  region.  The  mines 
repeatedly  reached  caves,  into  which  the  mine-water  could  be 


THE    GENESIS    OF    ORE-DEPOSITS.  101 

discharged  without  filling  them,  there  being  some  subterranean 
outlet.  But  these  caves,  as  I  have  explained  in  Part  I.,  were 
formed  by  descending  liquids  of  the  vadose  circulation ;  and 
to  assume  a  similar  origin  for  the  cavities  filled  by  the  ore- 
bodies  would  be  to  assume  that  the  latter  cavities  were  formed 
in  a  manner  directly  opposite  to  that  in  which  they  were  filled 
— which  is  highly  improbable. 

It  was  not  until  later,  when  I  had  become  acquainted  with  the 
observations  of  J.  Noggerath  (cited  in  Part  I.)  on  the  thermal 
springs  of  Burtscheid,  that  I  recognized  that  ascending  mineral 
springs  are  able  to  cut  their  own  way  to  the  surface,  forming 
the  channels  which  they  ultimately  fill  with  ore.  The  most 
difficult  feature  of  all,  namely,  the  nearly  cylindrical  form  of 
the  ore-bodies  of  Yalle  Sacca,  wras  thus  satisfactorily  ex- 
plained. 

The  channel  of  the  Reichenstein  body  runs  vertically  for  400 
meters  (1312  feet)  in  limestone  between  greenstone  dikes ;  or, 
in  other  words,  in  a  zone  of  lime  between  two  zones  of  im- 
permeable rock.  The  dikes  therefore  control  its  direction.  It 
follows  downward  nearly  at  the  angle  of  their  steepest  dip,  but 
with  a  pitch  southward,  giving  it  a  "  false  dip." 

The  sections  of  the  various  workings  show  that  the  ore-body 
apparently  ended  at  one  side  of  the  dike  and  recommenced  at 
the  other  side,  as  if  it  had  passed  through.  In  that  case, 
porous  places  in  the  dike-mass,  at  the  intersection,  will  have 
determined  the  track  of  the  channel.  It  is  significant  that  the 
Reichenstein  ore-channel  passes  in  depth  through  the  dikes 
to  the  SW.,  towards  what  is  probably  a  great  fault-fissure,  and 
not  in  the  direction  of  the  present  drainage.  Nor  could  the 
former  deep  drainage  from  this  channel  have  been  to  the 
NE.  along  the  contact  between  the  limestone  and  the  underly- 
ing Liassic  sandstone  (which,  in  fact,  appears  at  a  lower  level, 
where  the  Yalle  Sacca  joins  the  Galbina  valley),  for  the  reason 
that  all  the  barriers  of  the  greenstone  dikes,  unquestionably 
extending  from  the  limestone  into  .the  sandstone,  would  have 
opposed  that  flow.  The  stratigraphical  conditions  thus  exclude 
the  possibility  that  this  channel  was  formed  by  vadose  circula- 
tion, and  render  more  probable  the  view  that  it  owes  its  origin 
to  the  ascending  waters  of  the  deep  circulation,  which  certainly 
affected  the  filling  of  it. 


102  THE    GENESIS    OF    ORE-DEPOSITS. 

Haibl. — Raibl,  in  Carinthia,  is  the  best  representative  of  a 
group  of  deposits  which  were  at  a  recent  period  taken  to  be 
genuine  beds  even  by  Y.  M.  Lipold,*  then  the  best  authority 
on  the  mines  of  the  Alps  in  general.  Here  and  there,  as,  for 
instance,  by  A.  Morlot,f  observations  were  made  which  threw 
some  doubt  on  this  conception  ;  but  since  they  did  not  fit  into 
the  prevailing  system,  the}7  remained  disregarded.  It  was  my 
fortune  to  establish  the  truth  of  the  situation.  Prof,  von  Grod- 
deck  kindly  characterized  my  investigation  of  it  as  "  opening 
a  new  path,"  and  adopted  the  filling  of  spaces  of  dissolution  as 
a  class  in  his  system  (op.  cit.,  pp.  10,  236,  etc.). 

Such  deposits  occur  in  Carinthia,  in  an  E.-W.  limestone 
alpine  range,  of  which  Raibl  is  the  western  end;  and  also 
somewhat  further  north,  in  the  zone  of  Bleiberg,  near  Yillach, 
chiefly  in  a  limestone,  early  denominated  for  this  reason  the 
ore-bearing  limestone,  and  more  recently  determined  as  Tri- 
assic. 

The  ores  occurred  mostly  in  the  vicinity  of  certain  inter- 
calated slates,  which  seemed  always  to  occupy  the  same  "  Raibl 
horizon,"  and  thus  led  to  the  conclusion  that  the  ore-deposits 
(naturally  believed  to  be  of  contemporaneous  origin)  likewise 
occupied  a  fixed  horizon.  But  it  soon  appeared  that  the  slate 
at  Bleiberg  belonged  to  a  somewhat  different  horizon  in  the 
Trias  ;  and  I  ventured  to  assert  that  the  impermeability  of  the 
slates,  as  compared  with  the  solubility  of  the  limestone,  had 
had  something  to  do  with  the  ore-deposition,  which  was  a  sec- 
ondary formation  in  the  rocks. 

There  are  found  at  Raibl,  some  distance  below  the  slates,  in 
the  limestone  which  conformably  underlies  them,  what  seem 
indeed  at  first  glance  to  be  beds  of  ore.  They  consist  chiefly 
of  a  coarsely  crystalline  galena,  with  pyrites,  and  a  zinc-blende 
(wurtzite)  in  very  thin  crusts,  hence  called  Schalen blende.  A 
closer  study,  however,  of  the  extremely  distinct  crustification 
reveals  that  it  does  not  represent  the  stratification,  which,  on 
the  contrary,  it  crosses  at  all  angles,  being  in  fact  the  filling  of 
irregular  spaces,  traversing  the  limestone  in  every  direction. 

Further  light  is  furnished  by  the  seams  which  here  occur. 
As  is  generally  the  case  in  limestone,  these  are  rarely  wide 

*  Jahrb.  d.  k.  k.  g.  E.  Anst.,*1862,    Verh.,  p.  292. 
t  Ibid. ,1850,  i.,p.  266. 


THE    GENESIS    OF    ORE-DEPOSITS.  103 

fissures,  but  usually  mere  partings  between  two  polished  walls 
in  close  contact.  Slickensides,  etc.,  identify  them  at  once  as 
results  of  friction,  caused  by  the  forcible  rubbing  together  of 
walls  perhaps  originally  irregular.  The  plane  of  contact  with 
the  slates  offers  a  means  of  determining  the  extent  of  the 
movement  along  some  of  these  insignificant-looking  seams; 
and  it  appears  that  dislocations  as  great  as  40  to  60  meters  (131 
to  196  feet)  have  thus  taken  place.  Since  the  slates  possess 
some  flexibility,  they  were  sharply  bent  in  the  immediate 
neighborhood  of  the  fault,  a  feature  which,  on  account  of  its 
theoretical  importance,  I  have  illustrated  in  Fig.  69. 

In  the  seams  themselves  (locally  called  Blatter  or  "  leaves  ") 
there  can  be,  of  course,  no  deposit  of  ore ;  but  such  deposition 
occurs  outside  of  the  fissure,  when  soluble  rocks  like  this  lime- 
stone are  traversed.  Geode-spaces  were  thus  leached  out,  and 
are  found  filled  with  distinct  mineral  crusts,  as  is  shown  in  Fig. 
72,  representing  the  face  of  a  level  on  the  so-called  Johanniblatt. 

It  cannot  be  doubted  that  the  ore-supply  came  from  the 
seams ;  and  when  we  find  such  seams  also  in  large  and  rich 
deposits  of  similar  character,  like  those  on  the  north  slope  of 
the  Konigsberg  at  Raibl,  we  must  concede  to  them  a  similar 
significance  as  regards  the  ore-deposition. 

To  the  more  important  of  these  seams,  J.  Waldauf  von 
Waldenstein*  and  Dr.  "W.  Fuchsf  had  already  called  attention. 
These  are  the  Morgen,  Abend,  Johann  and  Josef.  The  first 
three  meet  at  an  angle  of  about  30°,  and  form  the  boundaries 
of  ore-bodies,  extending  downwards  along  the  seams  with  a 
horizontal  length  of  40  to  80  meters  (131  to  262  feet)  and  a 
total  thickness  (including  portions  too  poor  to  work)  of  10  to 
50  meters  (33  to  164  feet).  Many  of  the  mine-managers  be- 
lieved that  there  was  here  a  continuous  ore-bed  which  had 
been  faulted  into  separate  bodies  by  the  seams,  and  numerous 
exploring  levels  were  undertaken  to  develop  this  assumed  bed, 
but  all  in  vain.  Nothing  was  found,  except  a  few  more  or  less 
independent  ore-shoots  on  one  or  both  sides  of  the  seams, 
similar  to  those  which  have  been  encountered  in  recent  years 
at  Leadville. 

*  Die  besonderen  Lagerstdtten  d.  nutzb.  Mineralien,  Vienna,  1824,  Plate  III., 
Fig.  4. 

f  Beitrage  zur  Lehre  von  den  Erzlagerstdtten,  Vienna,  1846,  Plate  I.,  p.  23. 


104  THE    GENESIS    OF    ORE-DEPOSITS. 

The  foregoing  observations  will  facilitate  a  comprehension 
of  Figs  67  and  68,  the  former  showing  a  section  (not  strictly 
in  one  plane)  of  the  ore-shoots  in  the  government  mine,  and 
the  latter  a  similar  picture  of  the  Struggl  private  mine.  In  the 
former,  separate  ore-bodies  are  observed  to  the  distance  of  500 
meters  (1640  feet)  above  the  bottom  of  the  valley,  and  in  1870 
the  continuous  ore-shoots  extended  from  425  meters  (1394  feet) 
above  to  150  meters  (492  feet)  below  that  level,  a  total  vertical 
height  of  575  meters  (1886  feet). 

It  will  be  seen  that  the  several  portions  of  the  slopes  descend 
more  or  less  parallel  with  the  stratification  and  the  lime-slate 
contact,  but  with  steps  or  offsets.  The  highest  portion  of  the 
Abendblatt  ore-shoot  is  about  300  meters  (984  feet)  in  the  foot- 
wall  of  the  slate-contact ;  at  greater  depths  there  are  portions 
130,  150,  85  and  finally  10  meters  only  (426,  492,  279  and  33 
feet)  from  that  plane. 

It  thus  appears  that  the  ore-shoots  are  approaching  the  con- 
tact in  depth,  and  will  probably  follow  it  below.  It  is,  there- 
fore, not  here  the  case  that  a  particular  layer  in  the  limestone 
has  favored  the  formation  of  spaces  of  dissolution.  If  that 
were  true,  the  ore-body,  notwithstanding  the  convergence  of 
the  seams  southward,  should  maintain  a  more  or  less  uniform 
distance  from  the  contact,  which  it  does  not  do,  either  in  the 
section  of  Fig.  67  or  in  that  of  the  Struggl  mine,  Fig.  68,  where 
the  opposite  occurs,  namely,  the  ore-shoots  depart  from  the 
contact  in  depth.  I  must  confess  myself  unable  to  explain 
these  variations  in  the  Raibl  ore-shoots  with  the  light  afforded 
by  the  mine-workings  down  to  1870.  But  I  am  convinced  that 
the  explanation  will  be  found  by  further  thorough  study. 
Meanwhile,  I  can  only  claim  the  credit  of  having  placed  the 
inquiry  upon  what  I  deem  to  be  the  true  road,  and  express  my 
regret  that  in  the  twenty  years  since  the  publication  of  my 
monograph  on  the  Raibl  deposits  no  further  progress  seems  to 
have  been  made  in  the  interpretation  of  the  very  numerous 
analogous  ore-deposits. 

The  North  of  England. — I  cannot  omit  to  mention  here  the 
region,  classic  in  this  respect,  of  the  North  of  England.  Lead 
mining  is  actively  carried  on  in  the  carboniferous  limestone  of 
Northumberland,  Durham,  Cumberland  and  Westmoreland, 
where  the  limestone  alternates  with  sandstone  and  slate,  and 


THE    GENESIS    OF    ORE-DEPOSITS.  105 

occasional  intercalated  eruptives  or  their  tufas.  This  forma- 
tion is  traversed  and  faulted  by  a  variety  of  seams  and  veins ; 
and  the  veins  are  generally  richer  where  they  are  in  the  lime- 
stone. The  thinner  and  more  extensively  faulted  of  the  lime- 
stone strata  are  entirely  severed,  so  that  they  appear  in  dif- 
ferent horizons  on  opposite  sides  of  the  faulting-fissure. 
Where  they  are  thicker  or  less  widely  thrown  by  the  fault, 
however,  limestone  appears  on  both  sides  of  the  latter.  It  is 
obvious  that  an  accurate  picture  of  these  conditions  would 
furnish  valuable  data  concerning  the  ore-genesis. 

The  several  descriptions  of  the  mines  do  not  specify  whether 
the  ore  of  such  veins  as  become  rich  in  the  limestone  occurs  in 
the  fissures  proper  or  outside  of  them  in  spaces  of  dissolution 
in  the  limestone.  The  latter  is  clearly  the  case  in  the  so-called 
"  flats."  In  certain  horizons,  where  the  seams  encounter  the 
soluble  lime-stratum,  the  ore-filling  departs  from  the  fissure 
into  the  geodes  of  the  rock,  forming  frequently  very  rich  ore- 
bodies  of  highly  irregular  form,  but  flat,  by  reason  of  their 
following  the  soluble  stratum.  The  ore-filling  continues  to  a 
very  uncertain  distance  from  the  fracture-plane,  and  is  gener- 
ally accompanied  with  frequent  cavities,  the  walls  of  which  are 
covered  with  crusts  of  calcite,  blende  and  galena.  Empty 
caverns  also  occur.*  We  cannot  but  recognize  immediately 
in  this  description  the  type  as  to  character  and  position  of  the 
Raibl  deposits,  the  druses  of  which  are  here  represented  by  the 
incrusted  cavities.  The  empty  caverns  have  doubtless  been 
formed  by  subsequent  processes  of  dissolution. 

These  phenomena  occur  in  the  North  of  England  on  a  very 
large  scale.  Veins  are  mentioned  which  have  been  traced  for 
several  miles,  and  the  connected  subterranean  channels  of  dis- 
solution must  be  also  of  considerable  length.  The  existence 
of  laterally  extensive  ore-channels,  and  hence  of  an  under- 
ground circulation  of  mineral  waters  not  formerly  suspected 
is  thus  revealed,  and  an  entirely  new  light  is  thrown  upon  the 
so-called  "  ore-beds." 

These  observations  are  confirmed  in  another  quarter  by  de- 
velopments in  Western  North  America,  where  very  numerous 

*  See  J.  A.  Phillips,  Ore-Deposits,  p.  180;  also,  D.  C.  Da  vies,  Metalliferous 
Minerals  and  Mining,  London,  1880,  p.  216  ;  and  the  works  of  W.  Wallace,  T. 
Sopwith,  Westgarth  Foster,  C.  E.  De  Kance,  E.  Hunt,  etc. 


106  THE    GENESIS    OF    ORE-DEPOSITS. 

ore-deposits  are  connected  with  limestone.  It  is  impossible  to 
bring  forward  here  the  whole  of  this  material.  I  must  limit 
myself  to  certain  localities,  which  have  been  thoroughly  studied 
and  described  in  publications. 

Leadville. — I  will  begin  with  Leadville,  the  recent  blossom  of 
the  mountain-world  of  Colorado.  I  am,  indeed,  not  person- 
ally acquainted  with  this  locality,  the  importance  of  which  was 
not  recognized  until  after  my  visit  to  the  United  States ;  but 
my  lively  interest  in  it  is  testified  by  the  article  concerning  it, 
which  I  laboriously  compiled  in  1879  from  the  incomplete  data 
then  available.*  Later,  when  S.  F.  Emmons  had  finished  his 
surveys,  but  before  the  publication  of  his  epoch-making  work,f 
I  had  opportunity  to  exchange  views  with  him  concerning  the 
genetic  condition,  and  to  confess  that  I  was  unable  to  share  his 
opinion  as  to  the  downward  course  of  the  mineralizing  solu- 
tions— an  opinion  which  was  opposed  to  the  then  prevalent  be- 
lief. The  mine-workings  have  been  greatly  extended  since  that 
time,  and  Emmons's  suggestion  has  been  shown  by  several 
mining  engineers,}  on  the  basis  of  thorough  studies  under- 
ground, to  be  untenable ;  so  that  the  Leadville  deposits  appear, 
as  regards  the  origin  of  their  metallic  contents,  to  form  no  ex- 
ception to  the  history  of  other  similar  deposits.  I  think  Em- 
mons himself  must  have  acknowledged  the  force  of  these 
criticisms,  which  do  not  detract  in  the  least  from  the  merit  of 
his  accurate  investigation  of  the  district. 

On  the  west  slope  of  the  Mosquito  range  appears  a  series  of 
undulating  Palaeozoic  strata,  with  heavy  layers  and  intrusive 
masses  of  eruptive  rocks,  and  traversed  by  numerous  faults. 
This  formation  covers  a  large  area,  only  a  comparatively  small 
portion  of  which,  namely,  the  vicinity  of  Leadville,  is  ore- 
bearing, — a  circumstance  which  of  itself  points  to  a  local  origin 
for  the  ore.  As  is  well-known,  the  series  of  rocks  has  the  fol- 
lowing order  downwards  :  white  porphyry,  blue  limestone,  gray 
porphyry,  white  limestone,  lower  quartzite, — which  I  will  de- 

*  "Leadville,  die  neue  Bleistadt  in  Colorado."— Oesterr.  Zeitsch.,  1879. 

t  "  Geology  and  Mining  Industry  of  Leadville." — U.  S.  Geol.  Survey,  Monogr. 
xii.,  Washington,  1886. 

t  F.  T.  Freeland,  "The  Sulphide -Deposits  of  South  Iron  Hill."— Trans.  A.  I. 
M.  E.,  1885,  xiv.,  181  ;  C.  M.  Kolker,  "The  Leadville  Ore-Deposits."—  Ibid.,  p. 
273;  A.  A.  Blow,  "The  Geology  and  Ore-Deposits  of  Iron  Hill."—  Ibid.,  1889, 
xviii.,  145. 


THE    GENESIS    OF    ORE-DEPOSITS.  107 

note,  for  brevity,  by  their  initial  letters.  The  ore-deposits  occur 
chiefly  at  the  contact  between  the  first  two  members  of  the 
series,  below  the  WP.  and  above  the  BL.  In  the  upper  levels 
they  are  oxidized  and  chloridized  (doubtless  in  this,  as  in  other 
places,  through  the  action  of  descending  ground-water);  in 
lower  levels  they  appear  in  their  original  form  as  sulphides. 
That  this  was  the  condition  in  which  they  were  originally  pre- 
cipitated, Emmons  admits ;  only  their  position  seems  to  him 
to  exclude  the  hypothesis  of  ascending  solutions.  He  says  (op. 
cit,  p.  573)  : 

"  The  principal  water-channel  at  the  time  of  deposition  was  evidently  the  upper 
contact  of  the  blue  limestone  with  an  overlying  porphyry  ;  and  from  this  surface 
they  penetrated  downwards  into  the  mass  of  the  limestone.  It  may  be  assumed, 
therefore,  that  the  currents  were  descending  under  the  influence  of  gravity,  rather 
than  ascending  under  the  influence  of  heat." 

But  he  omits  to  explain  how  he  conceives  it  possible  that 
mineral  solutions  descending  by  gravity,  and  hence  certainly 
having  been  in  contact  with  the  surface-region,  could  deposit 
sulphides.  Assuming  such  an  explanation  to  be  furnished  by 
reduction  through  organic  substances,  the  question  arises 
whither  such  descending  currents  could  go.  Here  the  theory 
is  in  conflict  with  our  conception  of  the  underground  circula- 
tions. 

As  A.  A.  Blow  has  shown,  however,  a  leaching  of  the  WP. 
cannot  by  any  means  have  supplied  the  ore ;  for  this  rock  is 
not  at  all  decomposed,  as  in  that  case  it  must  have  been.  On 
the  other  hand,  there  are  found  in  the  intrusive  beds  and  dikes 
of  the  lower  GP.  various  indications  that  this  rock  had  more 
to  do  with  the  ore-deposition.  Along  these  dikes  lie  the  ore- 
shoots, — in  other  words,  the  channels  in  which  ore  was  de- 
posited. 

It  was  at  first  tacitly  assumed  that  the  ore  occupied  the 
whole  plane  of  the  contact,  although  it  was  known  that  the 
richest  bodies  occupied  particular  zones  in  this  plane.  The  im- 
portance of  these  ore-shoots  was  recognized  later ;  and  we  may 
now  consider  the  Leadville  occurrence  as  presenting,  not  a 
single  contact-deposit  or  ore-bed,  but  a  complex  group  of  ore- 
shoots,  such  as  we  have  observed  in  other  ore-deposits  in  lime- 
stone. These  ore-shoots  lie,  in  Leadville,  at  the  contact  be- 
tween the  soluble  and  the  eruptive  rock;  while  in  Raibl  they 


108  THE    GENESIS    OF    ORE-DEPOSITS. 

appear  near  the  contact  of  two  stratified  rocks,  one  soluble  and 
the  other  impermeable.  The  physical  process  forming  these 
ore-shoots  was  doubtless  the  same  in  both  cases.  The  mineral 
solutions,  ascending  under  pressure,  and  seeking  a  path  to  the 
surface,  followed,  as  some  would  say,  the  line  of  the  least  re- 
sistance ;  or,  as  I  would  prefer  to  express  it,  there  was  estab- 
lished in  the  soluble  rock  a  line  of  maximum  circulation,  re- 
sulting in  the  dissolving-out  of  a  channel. 

Such  dissolution,  however,  occurred  not  only  on  the  contact 
between  "WT.  and  BL.,  but  also  at  other  contacts.  Thus  L.  D. 
Bicketts  (Rolker,  1.  c.,  p.  284)  gives  a  section  of  a  mine  on  Car- 
bonate Hill,  showing  a  second,  deeper  ore-horizon  between  the 
G-P.  (dike  porphyry)  and  the  underlying  limestone.  According 
to  Rolker,  the  BL.  of  Fryer  Hill  was  relatively  thin,  and  has 
been  replaced  with  ore  and  accompanying  minerals,  all  but 
small  remnants  of  dolomitic  sand.  These  are  generally  above 
the  ore,  i.e.,  along  the  upper  contact,  whereas,  according  to  Em- 
mons's  theory,  they  should  be  replaced  with  ore. 

The  sections  given  by  F.  T.  Freeland  (L  c.,  Figs.  1  and  6) 
show  two  ore-horizons,  the  thicker  of  which  is  below  the 
"WT.,  and  the  other  below  an  intrusion  of  GrP. ;  and  Mr.  Blow's 
sections  from  Iron  Hill  reveal  similar  phenomena  (see  Fig.  73, 
a  section  through  the  McKean  shaft).  The  ore-shoots  are,  of 
course,  irregular  in  form ;  but  a  main  general  direction  can  be 
recognized,  which  is  eastward  in  Fryer  Hill,  but  northeastward 
in  Carbonate  and  Iron  Hill,  representing  the  course  of  the 
channel  through  which  the  mineral  solutions  circulated. 

In  the  data  at  hand  concerning  the  structure  of  the  de- 
posits, nothing  is  said  of  a  distinct  crustification.  It  is  to  be 
remembered,  of  course,  that  mining  operations  hitherto  have 
been  largely  confined  to  the  upper  and  decomposed  zone, 
whereas  this  phenomenon,  if  ever  so  fully  developed,  would 
show  itself  clearly  only  in  the  undecomposed  zone.  When  we 
read,  however,  of  great  "  horses  "  of  country-rock,  encountered 
in  the  midst  of  the  ore,  we  must  believe  that  the  deposit  is 
due  not  so  much  to  a  metasomatic  replacement  of  the  limestone 
as  to  the  filling  of  spaces  of  dissolution ;  and  hence  it  should 
exhibit  the  characteristic  sign  of  such  a  filling,  namely,  crusti- 
fication. It  seems  to  me  that  this  *  point  has  not  received  the 
attention  it  deserves ;  and  I  hope  that  observations  in  the  un- 


THE    GENESIS    OF    ORE-DEPOSITS.  109 

decomposed  ore-zones  will  give  more  definite  data  as  to  struc- 
ture. It  is  difficult  to  believe  that  metasomatic  processes  could 
produce  such  pronounced  ore-shoots  as  those  described  at  Lead- 
ville. 

Impressed  by  Emmons's  views,  and  long  before  the  connec- 
tion of  the  ore-deposition  with  the  GP.  of  the  dikes  had  been 
shown,  I  wondered,  at  one  time,  whether  the  ore  might  not 
have  come  somehow  from  the  fault-fissures  into  the  contact- 
channels.  But  Mr.  Emmons  pointed  out  to  me  that  the  faults 
contain  only  ore  which  has  been  dragged  in  from  the  pre-ex- 
isting bodies,  the  formation  of  which  was  complete  before  the 
faulting  took  place. 

Conditions  analogous  to  those  of  Leadville  are  exhibited  in 
most  of  the  ore-deposits  in  limestone  occurring  in  the  Ameri- 
can "West.  But,  with  few  exceptions,  we  have  only  hasty  de- 
scriptions of  them,  and  sometimes  nothing  more  than  business 
"  puffs." 

Red  Mountain. — -A  remarkable  occurrence  has  been  described 
in  the  Red  Mountain  district,  Ouray  county,  Colorado.*  In 
the  midst  of  the  deposits  of  the  San  Juan  region,  which  are 
connected  with  eruptive  rocks,  appears  a  body  of  Mesozoic 
strata,  carrying,  at  the  contact  of  a  quartzite  with  the  under- 
lying limestone,  a  deposit  of  the  sulphides  of  iron,  lead,  cop- 
per, silver,  and  the  products  of  their  decomposition,  rich  in 
silver  and  somewhat  auriferous  (2110  to  3980  grammes  of  silver 
and  3  to  6  grammes  of  gold  per  metric  ton,  or  59  to  111  ounces 
of  silver  and  0.08  to  0.17  ounce  of  gold  per  ton  of  2000 
pounds).  At  certain  points  the  ores  extend  far  down  into  the 
limestone,  and  in  the  section  shown  in  Fig.  74  the  ore  follows 
a  fault-fissure  through  the  whole  thickness  of  the  limestone  into 
a  second  quartzite  stratum  below.  The  stratified  formation  is 
mostly  covered  with  andesite,  in  which  occur  ore-bearing  veins 
in  fissure-form. 

In  the  neighborhood,  at  Mineral  Farm,  another  contact-de- 
posit between  limestone  and  quartzite  is  known,  consisting  of 
barite  with  argentiferous  galena  and  tetrahedrite.  Both  the 
above  deposits  are  but  briefly  described,  and  perhaps  have  not 
been  extensively  worked.  Their  conditions  of  position  and  the 

*  G.  E.  Kedzie,  "The  Bedded  Ore-Deposits  of  Red  Mountain  District,"  Trans. 
A.  I.  M.E.,  1886,  xvi.,  570. 


110  THE    GENESIS    OF    ORE-DEPOSITS. 

predominance  of  lead-  and  silver-ores  strangely  remind  one  of 
Leadville. 

In  the  adjacent  Territories  of  New  Mexico  and  Arizona 
various  copper-deposits  occur  in  limestone,  and  at  its  contact 
with  eruptive  rocks ;  as,  for  instance  (according  to  the  outline- 
description  of  A.  F.  Wendt*),  in  the  Clifton  and  Bisbee  dis- 
tricts. The  sections  accompanying  Mr.  Wendt's  paper  remind 
me  of  some  of  the  deposits  described  in  my  monograph,  at 
Rezbanya,  at  Mednorudjansk,  and  at  Bogoslavsk  in  the  Ural. 
Fig.  75  is  an  interesting  section  from  the  Clifton  district,  in 
Arizona,  showing  two  steep  ore-shoots,  parallel  with  the  felsite 
dike,  and  a  flat  one,  parallel  with  the  bedding. 

Utah. — With  respect  to  Utah,  the  paper  of  0.  J.  Hollisterf 
gives  a  general  survey  of  the  deposits  of  the  Territory,  and 
mentions  a  number  which  occur  in  limestone.  Some  of  those 
in  central  Utah  I  have  had  the  opportunity  to  see  personally, 
during  the  period  when  mining  was  still  confined  chiefly  to  the 
decomposed  upper  levels.  I  refer  to  the  Prince  of  Wales  and 
the  Reed  and  Benson,  in  Big  Cottonwood ;  the  Emma  and  the 
Flagstaff,  in  Little  Cottonwood ;  the  Old  Telegraph,  in  West 
Mountain,  and  the  Hidden  Treasure,  in  Dry  Canon  district. 

Palaeozoic  strata  are  here  traversed  by  frequent  eruptive 
dikes,  and  by  two  intersecting  systems  of  faults.  The  ore- 
deposits,  of  varying  thickness,  in  the  limestone  have,  as  a  rule, 
the  form  of  "  chimneys,"  either  lying  flat,  with  the  bedding,  or 
standing  steeply  along  the  dikes  and  faults.  This  gave  rise  in 
the  beginning  (when  the  nature  of  the  deposits  was  not  under- 
stood, and  the  conception  of  a  typical  "  lode  "  generally  pre- 
vailed) to  a  series  of  disappointments  and  mistakes  in  mining, 
of  which  the  history  of  the  Emma  mine  furnishes  an  interest- 
ing example.  Apparently  the  irregularity  and  the  complica- 
tions of  these  deposits  came  to  be  better  known  afterwards. 

The  (sometimes  very  rich)  ores  consist  chiefly  of  sulphides  of 
lead  and  silver,  and  the  products  of  their  decomposition.  In 
some  cases  (e.g.,  Hidden  Treasure)  cuprite  occurs,  with  native 
copper ;  and  in  the  Camp  Floyd  district  cinnabar  also  is  found. 

Nevada. — In  Nevada,  adjoining  Utah  on  the  west,  deposits 
of  this  class  are  likewise  abundantly  represented.  I  will  men- 

*  "The  Copper-Ores  of  the  Southwest,"  Trans.  A.  I.  M.  E.,  1886,  xv.,  25. 
t  "Gold-  and  Silver-Mining  in  Utah,"  Trans.,  A.  I.  M.  E.,  1887,  xvi.,  3. 


THE    GENESIS    OF    ORE-DEPOSITS.  Ill 

tion  only  the  two  districts  which  have  been  most  thoroughly 
studied,  namely,  White  Pine  and  Eureka. 

With  regard  to  the  former,  the  work  of  Arnold  Hague 
(1870)*,  demonstrating  the  peculiar  character  of  the  White 
Pine  deposits,  led  me  to  seek  for  European  analogues.f  I 
found  that,  apart  from  the  condition  of  the  ores,  which  at 
White  Pine  are  found  in  the  oxidized  and  chloridized  zone, 
there  was  an  analogy  with  all  the  European  ore-deposits  in 
limestone,  but  especially  with  the  conditions  at  Raibl. 

Devonian  limestones  and  calcareous  slates  are  overlain  at 
White  Piixe  by  Carboniferous  clay-slates,  sandstones  and  lime- 
stones ;  and  the  ores  occur  only  in  Devonian  limestone  and  at 
its  contact  with  the  calcareous  slates  on  a  N".  and  S.  anticlinal. 
The  ores  and  the  associated  minerals  (quartz,  calcite,  gypsum, 
fluorspar,  barite,  rhodonite,  rhodochrosite,  with  the  chlorides, 
bromides,  oxides,  and  carbonates  of  various  metals,  especially 
silver,  lead  and  copper)  fill  the  cavities  in  the  limestone  and 
surround  its  fragments. 

The  various  mines  represent  different  stages  in  one  and  the 
same  process.  In  the  Eberhardt,  two  fissures  crossing  the 
anticlinal  bound  the  ore-body  (like  the  Morgenblatt  and  the 
Abendblatt  at  Raibl).  This  consists  of  a  lime-breccia  (Kalk- 
typhon),  the  fragments  of  which  fit  together,  and  are  cemented 
by  ore-bearing  quartz  seams.  The  Hidden  Treasure  mine  con- 
tained the  ore  in  geodes,  at  the  contact  of  the  limestone  and 
slate.  In  the  Aurora,  the  ore  was  in  bodies  stretching  ET.  and  S. 
In  Bromide,  Chloride  and  Pogonip  Flats,  the  ores  occurred  in 
geodes  and  masses  included  in  lime-breccia,  in  a  zone  parallel  with 
the  bedding.  It  is  Arnold  Hague's  opinion  that  the  Eberhardt 
mine  probably  represents  the  source  of  the  ore-solutions  which 
impregnated  the  limestone,  wherever  cavities  existed,  up  to  the 
level  of  the  overlying  calcareous  slates,  which  were  impermeable 
to  the  solution.  The  slate-cover  having  been  removed  by  ero- 
sion, the  ores  thus  accumulated  below  it  were  exposed  imme- 
diately at  the  surface ;  and  the  surprisingly  large  product  of 
the  district  was  derived  from  open  cuts  and  shallow  workings. 

*  "  Geology  of  the  White  Pine  District,"  U.  S.  Geol.  Surv.  of  the  40th  Parallel, 
vol.  iii.,  Mining  Industry,  p.  409. 

t  F.  Posepny,  ' '  Das  Erzvorkommen  vom  White  Pine  District,  u.  dessen  euro- 
paische  Analogien,"  Verh.  d.  k.  k.  g.  R.  A.,  1872,  p.  186. 


112  THE    GENESIS    OF    ORE-DEPOSITS. 

The  other  leading  analogue  in  Nevada  is  found  in  the  Eureka 
district,  and  was  made  widely  known  and  practically  significant 
by  the  law-suit  between  the  Eureka  and  Richmond  companies,* 
which  involved  the  definition  of  a  deposit  not  contemplated  in 
the  United  States  mining  law.  Similar  difficulties  have  arisen 
under  the  old  European  mining  codes.  Such  deposits  were 
known  in  some  districts  of  Europe,  but  they  were  not  so  widely 
distributed  as  the  fissure-veins,  for  the  conditions  of  which  the 
ancient  codes  were  framed.  Conflicts  were  therefore  inevita- 
ble. I  will  mention  only  Bleiberg  in  Carinthia  (which  presents 
some  degree  of  analogy  with  Eureka),  where,  besides  the 
general  mining  code,  special  statutes  became  necessary,  depart- 
ing from  the  usual  rules  with  regard  to  prospecting  and  the 
location  and  the  acquisition  of  claims. 

The  geological  conditions  of  the  district  have  been  described 
in  an  elaborate  monograph  by  J.  S.  Curtis, f  based  on  the  de- 
velopments existing  in  1882.  Further  knowledge  may  have 
been  gained  since,  but,  so  far  as  I  know,  nothing  later  has  been 
published.  I  made  a  brief  visit  to  Eureka  in  1876;  but  as  no 
comprehensive  maps  of  the  mine-workings  were  then  available, 
I  could  only  observe  in  a  general  way  the  analogy  with  Euro- 
pean deposits  examined  by  me. 

According  to  Arnold  Hague, J  the  series  here  occurring  of 
Prospect  Mt.  quartzite,  Prospect  Mt.  limestone,  Secret  Canon 
shale,  and  Hamburg  limestone  is  Cambrian.  The  ore  is  con- 
fined to  the  limestone  first  named,  and  in  particular  to  a  por- 
tion thereof  on  the  N.  E.  slope  of  Ruby  Hill,  enclosed  between 
two  fault-fissures.  The  features  of  the  NW.-SE.  ore-bearing 
zone  are  too  variable  to  be  indicated  by  a  normal  cross-section. 
Fig.  76  shows  a  generalized  and  Fig.  77  an  actual  section,  as 
represented  by  Curtis. 

The  main  fault-fissure  separates,  in  the  upper  level,  the  mas- 
sive limestone  in  its  hanging-  from  the  crushed,  ore-bearing 
limestone  in  its  foot-wall.  In  the  lower  levels  it  shows,  in  the 

*  E.  W.  Raymond,  "The  Eureka-Richmond  Case,"  Trans.  A.  I.  M.  E.,  1877, 
vi.,  371. 

t  "Silver-Lead  Deposits  of  Eureka,"  U.  S.  Geol.  Surv.,  Monogr.  vii.,  Wash- 
ington, 1884. 

J  "Abstract  of  Keport  on  the  Geology  of  the  Eureka  District,"  Third  Ann, 
Rep.  of  U.  S.  Geol.  Surv.,  1881-1882,  Washington,  1883,  p.  241. 


THE    GENESIS    OF    ORE-DEPOSITS.  113 

foot-wall,  quartzite  with  intercalated  "  Lower  shale,"  and  in 
the  hanging-wall,  further  down,  shale  and  quartzite.  An  ideal 
restoration,  above  the  present  saddle  of  Ruby  Hill,  of  the  foot- 
wall  rocks  which  have  been  removed  by  erosion,  would  bring 
to  light  a  relative  displacement  of  150  to  600  meters  (492  to 
1968  feet),  the  indications  being  that  the  foot-wall  has  been 
lifted.  This  would  explain  at  once  the  crushing  of  the  lime- 
stone in  the  foot-wall,  and  the  creation  of  a  second  fault  near 
the  contact  between  the  limestone  and  the  underlying  quartzite. 

The  ores  occur  chiefly  in  the  well-known  form  of  chimneys 
and  in  individual  masses,  mostly  interconnected  by  traces  of 
ore,  at  least  at  the  depth  where  the  two  faults  come  together. 
In  the  mines  to  the  SE.,  about  180  meters  (590  feet)  from  the 
Eureka-Blchmond  boundary,  the  fissures  come  together  at  the 
depth  of  about  400  meters  (1312  feet),  the  line  of  their  inter- 
section thus  dipping  gently  !N"W. 

The  ores  encountered  in  the  upper  zones,  above  water-level, 
were,  with  the  exception  of  a  few  insignificant  remains  of  sul- 
phides (mostly  argentiferous  galena),  oxidized  ores,  such  as 
cerussite  and  anglesite,  chlorides,  etc.,  carrying  a  considerable 
amount  of  silver  and  a  little  gold.  The  present  water-level 
follows  approximately  the  line  of  intersection  of  the  two  faults, 
but  the  fact  that  oxidized  ores  have  been  found  still  deeper  in- 
dicates that  the  water-level  was  once  lower  down. 

It  might  consequently  be  expected  that  caves  formed  by  the 
vadose  circulation  would  also  occur  at  considerable  depths, 
especially  as  the  whole  wedge  of  limestone  is  traversed  by  ore- 
shoots,  the  oxidation  of  which  would,  of  course,  give  occasion 
for  cave-formations.  The  newly-formed  caverns  would  often 
lie  along  the  ore-channels,  and  especially  in  their  upper  por- 
tions. (See  J.  S.  Curtis,  1.  c.,  p.  100.) 

Some  of  the  irregularly  distributed  ore-bodies  follow  rather 
the  quartzite-limestone  contact;  others  rather  the  main  fissures, 
with  a  N"W.  dip,  like  that  of  the  limestone  wedge.  Of  the  two 
largest  bodies,  which  have  furnished  the  chief  product  of  the 
district,  the  east  ore-body  exhibits  a  steep  SE.  pitch  for  nearly 
400  meters  (1312  feet),  and  the  west  ore-body,  for  nearly  an 
equal  distance,  a  flat  N.W.  pitch. 

In  considering  their  structure,  we  must  distinguish  sharply 
between  their  original  and  their  decomposed  condition.  The 


114  THE    GENESIS    OF    ORE-DEPOSITS. 

latter  often  hinders  a  clear  recognition  of  the  former.  The 
strata-like  deposits  of  cerussite  and  other  products  of  decompo- 
sition mentioned  by  Curtis  (1.  c.,  p.  98)  are  perhaps,  like  those 
in  my  sketch,  Fig.  78,  from  the  Old  Telegraph  mine,  remains 
of  the  original  crustification,  and  his  statement  (p.  104)  that 
"  when  the  ore  is  not  oxidized  there  are  no  signs  of  a  banded  or 
concentric  structure,  and  the  phenomena  observed  point  en- 
tirely to  substitution  of  the  sulphurets  for  country-rock,"  may 
thus  be  explained.  In  like  manner  his  assertion,  in  the  same 
place,  that  "  the  internal  structure  of  the  ore-masses  in  no  way 
resembles  those  of  Raibl,"  is  so  far  correct  that  the  original 
filling  is  at  Raibl  extraordinarily  distinct,  and  at  Eureka,  on  the 
contrary,  perhaps,  only  obscurely  traceable. 

I  personally  saw  in  the  Eureka  mine  some  small  ore-masses 
which  exhibited  crustification,  if  not  in  a  striking  degree,  yet 
sufficiently  to  be  recognized  by  an  impartial  observer.  Mr. 
Curtis  himself  (I.  c.,  p.  98)  says  that  "  rounded  boulders  of 
limestone  as  a  nucleus"  occasionally  occur  in  the  ore-mass,  and 
that  in  a  limestone-breccia  "  small  masses  of  ore  sometimes 
completely  fill  the  spaces  between  the  limestone  walls," — two 
phenomena  which  indicate  crustification,  and  are  explained  by 
the  hypothesis  of  a  filling  of  pre-existent  spaces. 

A  metasomatic  removal  of  the  limestone,  such  as  has  taken 
place  in  the  secondary  calamine-deposits  of  Raibl,  cannot  well 
be  supposed  for  the  original  ore-deposition  at  Eureka,  but  may 
have  attended  the 'formation  of  the  secondary,  decomposed 
products. 

I  believe  that  later  mining  in  deeper  zones  has  developed 
more  clearly  the  structure  of  the  original  Eureka  deposits,  and 
that  specimens  of  the  ore  have  shown,  after  polishing,  traces,  at 
least,  of  crustification. 

In  short,  I  consider  the  original  Eureka  ores  to  have  been 
deposited  in  pre-existing  spaces  by  ascending  mineral  solutions, 
while  their  decomposition  and  the  formation  of  the  caverns  are 
the  effects  of  descending  surface-waters. 

I  agree  with  Mr.  Curtis  that  the  ore-solutions  ascended  from 
the  deep  region  through  the  "  main-fissure  "  (which  has,  in  the 
NW.,  the  character  of  a  Blatt  at  Raibl,  and  in  the  SE.  part  of 
the  district  is  filled  with  rhyolite),  and  that  they  formed  and 
filled  the  ore-channels  in  the  soluble,  fissured  limestone. 


THE    GENESIS    OF    ORE-DEPOSITS.  115 

Missouri  and  Wisconsin. — We  have  dealt  thus  far  with  ore- 
deposits  in  mountain  districts,  where  tilting  and  folding,  as 
well  as  the  occurrence  of  eruptives,  betray  a  disturbance  of  the 
original  relations  of  stratification.  But  there  are  also  deposits 
in  limestone  in  plateau-regions,  where  the  strata  show  no  con- 
siderable disturbance.  Under  this  head  two  great  districts 
deserve  attention;  namely,  the  lead-regions  of  Missouri  and 
Wisconsin. 

Concerning  the  former,  we  may  refer  to  a  number  of  more 
or  less  detailed  descriptions.* 

We  have  in  this  case  not  a  perfect  plateau,  since  here  and 
there  domes  of  the  underlying  Archaean  come  to  the  surface, 
as  especially  in  the  continuation  of  the  Ozark  mountains ;  but 
the  predominant  character  is  nevertheless  that  of  a  structural 
plateau.  The  ore-deposits,  chiefly  confined  to  the  Silurian 
limestone,  are  in  part  primary  xenogenous  and  in  part  hyster- 
omorphous  (debris)  deposits;  the  latter,  as  is  well  known, 
consist  of  the  detritus  from  the  weathering  and  erosion  of  the 
outcrops  of  the  former.  In  the  former  we  find  all  the  phe- 
nomena encountered  in  the  deposits  of  mountain  regions.  One 
of  these  is  peculiarly  developed,  namely,  the  gently  inclined 
cavities  or  ore-channels,  shown  in  the  Valle  and  Bish  mines  of 
Jefferson  and  St.  Francis  counties,  concerning  which  J.  B-. 
Gage  has  given  some  (unfortunately  not  very  clear)  notes  and 
sketches. 

In  the  Valle  mines,  a  shaft  49.9  meters  (164  feet)  deep,  situ- 
ated 33.5  meters  (110  feet)  above  the  valley-bottom,  encoun- 
tered at  three  different  depths,  respectively  of  44.5,  46.3  and 
49.9  meters  (146, 151  and  164  feet),  flat-lying  ore-channels,  1  to 
2  meters  (3  to  6  feet)  wide,  which,  winding  in  different  direc- 
tions, produce  networks,  connected  at  the  intersecting  points 
by  chimneys  from  one  level  to  the  other.  The  cross-section  of 
these  channels  in  the  horizontal  limestone  or  dolomite  con- 
tracts sometimes  to  a  few  square  centimeters,  or  enlarges  to 

*  J.  R.  Gage,  "Lead-Mines  of  S.  E.  Missouri,"  Geol.  Surv.  of  Mo.,  1873-4,  p. 
603,  and  Tram.  A  L  M.  E.,  iii.,  116. 

G.  C.  Broadhead,  "TheS.  E.  Mo.  Lead-Districts,"  Ibid.,  p.  100. 

A.  Schmidt  and  A.  Leonhard,  "The  Lead- and  Zinc-Region  of  S.  W.  Mo.," 
Geol.  Surv.  of  Mo.,  1873-4,  p.  384. 

A.  Schmidt,    "  The  Lead-Region  of  Central  Missouri,"  Ibid.,  p.  503. 

8 


116  THE    GENESIS    OF    ORE-DEPOSITS. 

several  square  meters,  with  a  height  of  3  to  4  meters  (10  to  12 
feet). 

The  original  metallic  filling  was  galena,  pyrite  and  zinc- 
blende,  but  is  already  oxidized  to  cerussite,  anglesite,  smith- 
sonite  and  calamine,  which  are  accompanied  with  barite  and  a 
red  clay.  We  are  specially  interested  in  the  original  structure 
of  this  filling ;  but  this  is  not  easily  detected  in  the  mere  dia- 
grams at  hand. 

Figs.  32  to  35  reproduce  four  of  Mr.  Gage's  sections,  the 
first  three  being  Figs.  17,  18  and  19  of  his  paper  in  these 
Transactions,  and  the  fourth,  Fig.  72  of  his  article  in  the  report 
of  the  Missouri  survey.  They  indicate  for  both  the  metamor- 
phosed and  the  original  mineral  crusts  a  prevailing  horizontal 
position,  so  that  we  might  conclude  that  the  deposits  took  place 
in  cavities,  the  upper  portions  of  which  were  filled  with  gas 
only.  A  very  peculiar  formation  is  the  red  clay  which  in  some 
instances  covers  the  walls  of  the  caverns  and  surrounds  on  all 
sides  the  central  filling.  The  data  at  hand  afford  no  clue  to 
its  origin. 

Mr.  Gage's  description  of  Fig.  35  (I.  c.,  p.  618)  is  as  follows  : 

"Fig.  [72]  represents  the  occurrence  of  these  minerals.  The  solid  limestone 
contains  a  fissure,  entirely  filled  with  minerals  and  gangue.  The  minerals  are 
completely  enveloped  by  the  red  clay.  Above  are  two  thin  folds  of  silicate  of 
zinc,  separated  from  each  other  and  from  the  limestone  by  the  red  clay.  The 
folds  of  the  zinc-ore  are  sometimes  perfectly  solid,  being  from  one  to  six  inches 
thick,  and  consisting  of  alternate  layers  of  the  same  material  in  very  compact  folds  ; 
again,  the  mass  of  zinc-ore  is  from  one  to  six  inches  in  thickness,  but,  instead  of 
being  dense,  consists  of  a  thin  crust,  with  a  cavity,  whose  interior  walls  are 
lined  with  beautiful,  brilliant  crystals  of  the  silicate  and  occasionally  the  carbon- 
ate of  zinc.  More  rarely,  crystals  of  galena  are  in  the  cavities,  but  in  this  case 
are  invariably  covered  with  a  thin  coating  of  the  silicate ;  and  not  infrequently 
portions  of  the  cavities  are  partially  filled  with  red  clay,  highly  impregnated 
with  oxide  of  iron,  and  having  the  appearance  of  a  highly  decomposed  brown 
hematite.  Occasionally  heavy  spar  (barytes)  lies  in  a  dense  mass  in  close  contact 
with  the  zinc-ore ;  but  more  frequently  it  is  associated  with  the  galena.  Often, 
but  not  invariably,  immediately  below  the  folds  of  zinc-ore,  occur  irregular 
masses  of  the  zinc-ore  in  the  crystallized  form,  as  pseudomorphs  of  galena,"  etc. 

All  the/doubts  which  arise  concerning  the  mode  of  this  for- 
mation would  probably  be  solved  by  a  series  of  objective  pictures 
of  it ;  and  it  is  to  be  hoped  that  an  occurrence  so  interesting 
theoretically  will  be  accurately  recorded  before  it  is  too  late. 

The  deposits  occurring  near  the  "  islands  "  of  granite  and 


THE    GENESIS    OF    ORE-DEPOSITS.  117 

porphyry  have  special  interest.  While  the  Silurian  limestones 
of  the  surrounding  country,  farther  from  these  islands,  present 
chiefly  only  lead-  and  zinc-ores,  other  metals,  such  as  copper, 
cobalt,  and  nickel,  occur  as  the  Archaean  foundation-rocks  are 
approached;  and  this  circumstance  is,  to  my  mind,  an  indica- 
tion that  the  source  of  the  lead-deposits  also  is  to  be  sought  in 
depth. 

Mine  la  Motte. — As  an  example,  I  may  cite  the  district  of 
Mine  la  Motte,  to  which  I  once  made  a  brief  visit.  The  rock 
here  is  usually  the  same,  namely,  a  Cambrian  dolomite,  con- 
taining, however,  sandy  portions  and  a  clayey  stratum  charac- 
terized by  numerous  fossils  (Linguld).  The  ore  occurs  pre- 
dominantly as  an  impregnation  in  the  rock,  more  concentrated 
in  a  given  zone.  The  so-called  sandstone  does  not  here,  as  in 
other  instances,  cut  off  the  impregnation ;  it  is,  in  fact,  only  a 
sandy  limestone  and  dolomite,  and  its  carbonates  can  be  re- 
placed by  ore  as  well  as  those  of  adjoining  strata. 

I  thought  that  I  noticed  in  the  open  workings  called  the  Jack 
and  the  Seed-tick  diggings  a  very  remarkable  phenomenon; 
namely,  the  ore-impregnation  in  the  almost  horizontal  stratified 
rock  was  conformable  not  to  the  bedding  but  to  planes  crossing 
it  at  a  very  acute  angle  (about  10°).  A  pretty  long  terrace  was 
exposed;  and  the  impregnation-planes  cut  pretty  regularly 
through  the  sandy  dolomite  also.  This  appearance  indicates 
plainly  a  later  formation  of  the  ore,  independent  of  the  depo- 
sition of  the  rock-strata ;  and  one  is  almost  involuntarily  forced 
to  believe  that  it  was  the  former  ground-water  surface  which 
formed  the  cavities  to  be  impregnated.  But  it  was,  and  is,  in- 
conceivable to  me  how  these  cavities  could  be  filled  with  sul- 
phides ;  and  I  can  only  urge  that  occurrences  of  this  kind 
should  be  subjected  to  a  more  thorough  study  than  it  has  been 
in  my  power  to  give  to  them. 

Wisconsin. — In  Wisconsin,  and  in  parts  of  Iowa  and  Illinois, 
there  is  an  extensive  true  plateau,  the  calcareous  members  of 
which  contain  many  and  various  deposits  of  lead-  and  zinc- 
ores.  An  excellent  monograph  concerning  them,  by  my  es- 
teemed friend,  Prof.  J.  D.  Whitney,*  is  at  hand.  The  author 

*  Report  of  a  Geological  Survey  of  the  Upper  Mississippi  Lead-Region,  Albany, 
1862. 


118  THE    GENESIS    OF    ORE-DEPOSITS. 

seeks  to  show  that  the  mineral  solutions  depositing  these  ores 
came  from  above,  not  from  below.  He  appeals  to  the  circum- 
stance that  of  the  two  stratified  formations,  the  upper  and  the 
lower  Magnesian  limestone  (underlain  by  an  upper  and  a  lower 
sandstone,  respectively),  the  ores  occur  chiefly  in  the  upper,  and 
only  seldom,  and  in  small  quantity,  in  the  lower ;  while  the 
two  sandstones  (the  lower  of  which  is  assigned  to  the  Potsdam) 
do  not  reveal  any  traces  of  ore,  as  they  should  do  if  the  solu- 
tions had  come  from  below.  I  confess  that  this  conclusion  is 
not  obvious  to  me.  There  may  have  been  a  passage  through 
these  sandstones  at  a  distant  point,  not  yet  exposed ;  and  the 
mineral  solutions  may  have  found  or  created  spaces  in  the 
soluble  rock. 

The  argument  that  the  ores  must  have  come  from  above 
because  it  has  not  been  possible  to  discover,  in  the  Wisconsin 
region,  fault-fissures  and  eruptive  dikes,  such  as  have  brought 
up  similar  ores  in  the  north  of  England  and  other  places, 
seems  to  me  likewise  inconclusive.  And  as  little  can  I  accept 
the  explanation  of  an  occurrence  near  Dubuque,  discovered  by 
T.  Lavins  and  described  by  Whitney  (op.  tit.,  p.  291  and  Fig. 
on  p.  392),  which  I  reproduce  in  Fig.  79.  The  fragments  of 
galena,  crusted  with  cerussite,  which  hang  from  the  roof  of  a 
natural  cavern,  are  taken  as  a  proof  that  the  solutions  which 
deposited  them  must  have  come  from  above.  But  a  continua- 
tion of  this  cavern  is  indicated  in  the  bottom,  filled  with  clay, 
mixed  with  scattered  pieces  of  galena.  In  my  opinion,  this 
was  doubtless  originally  the  filling  of  a  vertical  fissure,  which 
was  enlarged  by  the  ground-water,  as  indicated  by  the  dotted 
line.  The  symmetrical  crusts,  as  I  suppose,  of  that  filling  were 
in  part  broken  up,  and  fell  into  the  clay  accumulating  in  the 
space  below;  while  the  upper  part  of  the  filling  remained  at- 
tached to  the  rock  of  the  roof. 

3.  METAMORPHOUS  DEPOSITS. 

Metamorphism  has  been  most  truly  defined  by  A.  de  Lap- 
parent  as  the  sum  of  the  chemical  changes  undergone  by  the 
sedimentary  rocks  after  their  deposition.  General  or  regional 
metamorphism,  affecting  the  rocks  over  wide  areas,  is  distin- 
guished from  local  or  contact-met&morphism,  caused  in  certain 
groups  of  strata  by  eruptive  intrusions.  In  studying  the  oc- 


THE    GENESIS    OF    ORE-DEPOSITS.  119 

currence  of  useful  minerals,  we  occupy  rather  the  local  stand- 
point, and  start  with  an  assumed  original  condition  of  the  rock, 
though  its  really  original  character  may  not  always  be  demon- 
strable— understanding  thereby,  for  our  purpose,  a  so-called 
typical  condition,  usually  shown  at  most  places  where  the  rock 
occurs. 

We  distinguish  the  replacement  of  some  constituents  of  a 
compound  rock,  for  which  the  term  "  impregnation  "  is  more 
appropriate,  from  the  replacement  of  the  whole  homogeneous 
mass  by  metasomasis.  But  since  every  rock  undoubtedly  con- 
tains small  primitive  cavities,  it  is  difficult,  and  sometimes 
impossible,  to  decide  whether  a  new,  xenogenous  substance 
has  not  been  deposited  in  such  pores ;  and  a  case  of  this  kind 
would  fall  under  our  notion  of  impregnation.  The  new  sub- 
stance may  indeed  have  found  entrance  through  the  pores,  if 
the  mineral  solutions  were  under  sufficient  pressure  to  over- 
come the  friction  of  their  walls,  at  least  in  the  line  of  least  re- 
sistance ;  and  these  solutions,  thus  introduced,  may  attack  and 
replace  one  or  another  element  of  the  rock.  The  entrance  of 
such  solutions  will  be  greatly  facilitated  by  the  fissuring  of  the 
rock,  whether  by  internal  or  external  forces.  AV  e  find  in  con- 
nection with  ore  veins,  and  also  with  the  thinnest  mere  seams, 
an  impregnation  of  the  country-rock,  which  Cotta  has  called 
subordinate  or  dependent  (unselbstdndige)  impregnation. 

The  particles  of  certain  substances  possess  a  peculiar  mutual 
attraction.  In  the  sandstone  of  Fontainebleau  occur  aggre- 
gates of  calcite  crystals,  which  have  come  together  in  spite  of 
the  separating  medium  of  sandstone;  and  in  a  similar  way,  as 
we  have  seen,  another  substance  of  strong  crystallizing  power, 
namely,  galenite,  forms,  in  the  pipe-ores  and  script-ores  of 
Raibl,  crystalline  masses,  in  spite  of  the  intervening  diaphragm 
of  a  foreign  medium. 

In  like  manner  are  formed  the  so-called  concretions,  the  cal- 
careous and  marly  masses  (Losskindleiri)  in  the  Loess,  and  the 
Marleker  of  the  ancient  Scandinavian  beaches.  For  the  for- 
mation of  the  former,  occasion  was  given  by  decaying  plant- 
roots  ;  for  that  of  the  latter,  by  various  animal  remains,  mussels, 
fishes,  etc.  In  Norway,  they  have  preserved  a  complete  fauna 
of  the  Glacial  and  post-G-lacial  epochs. 

Similarly,  we  find  in  some   spherosiderite   concretions  of 


120  THE    GENESIS    OF    ORE-DEPOSITS. 

the  Saarbriicken  coal-basin  the  remains  of  fishes.  A  discerni- 
ble nucleus  is  not  always  found  in  such  concretions ;  sometimes 
no  cause  for  this  peculiar  formation  can  be  discovered.  The 
concretions  occurring  in  stratified  rocks  are  usually  lenticular, 
comprising  portions  of  several  similar  strata.  Even  spherical 
forms,  resembling  pisolites,  occur. 

If  we  imagine,  for  instance,  spherosiderite  concretions 
formed  closely  side  by  side  in  one  stratum,  we  shall  have  a 
regular  bed  of  clay-ironstone.  Leaving  out  of  view  the  agency 
of  fissures,  or  contacts  with  intruded  rocks,  impregnations  fol- 
lowing certain  strata  may  be  formed,  constituting  a  second  kind 
of  ore-beds.  A  third  kind  may  result  from  the  more  or  less 
complete  replacement  of  the  original  rock,  especially  when  the 
latter  is  a  soluble  precipitate,  like  gypsum  or  limestone.  In 
thick  limestone  formations  the  ore-beds  occur  at  the  contact 
with  insoluble  rocks,  as  at  Rodna. 

In  all  these  cases  the  deposits  have  the  form  of  a  bed,  but 
the  ores  rarely  cover  the  whole  contact-surface,  occupying,  on 
the  contrary,  only  certain  zones  of  it.  In  other  words,  in 
these  as  in  other  deposits,  ore-shoots  occur. 

Much  more  complicated  relations  result  when  the  mineral 
solutions  ascend  along  structural  fissures  and  rock-contacts ; 
and  in  order  to  a  comprehensive  description  of  this  suite  of 
phenomena,  it  will  be  well  to  consider  first  the  simpler  condi- 
tions obtaining  in  soluble  rocks,  and  afterwards  the  more  com- 
plex occurrence  of  such  deposits  in  crystalline  and  eruptive 
rocks.  We  will,  therefore,  review  the  metamorphous  deposits 
as  they  occur  in  (a)  distinctly  stratified  rocks ;  (6)  soluble  pre- 
cipitates ;  and  (c)  crystalline  schists  and  eruptive  rocks. 

a.  Metamorphous  Ore-Deposits  in  Distinctly  Stratified  Rocks. 

We  find  in  unquestionable  sediments  not  only  metallic  oxides 
and  salts,  but  also  sulphides,  in  the  form  of  ore-beds  which,  by 
reason  of  this  stratigraphical  relation,  have  been  held  to  be  of 
contemporaneous  origin,  that  is,  idiogenous.  As  a  consequence, 
it  has  been  necessary  to  assume  that  they  were  precipitated  in  a 
sea-basin,  in  which,  before  and  after  their  precipitation,  only 
barren  sediments  were  deposited.  These  metals  must,  there- 
fore, have  been  dissolved  in  the  water  of  the  basin,  and  that  in 
very  large  quantity,  as  indicated  by  the  frequently  great  thick- 


THE    GENESIS    OF    ORE-DEPOSITS.  121 

ness  of  the  ore-beds.     But  for  such  an  assumption  we  have  no 
present  analogy. 

The  Deposition  of  Ores  from  Sea-  Water. — In  this  particular, 
however,  we  have  to  do  rather  with  suggestions  than  with 
demonstrations  of  fact.  So  far  as  sea-water  is  concerned, 
traces  of  metals  have  been  found  in  the  water  itself,  in  the 
ashes  of  marine  plants,  and  in  the  solid  constituents  of  marine 
animals,  for  instance,  corals  by  Malagutti,  Bibra,  and  Forch- 
hammer.*  Traces  of  silver,  iron  and  manganese  were  de- 
tected in  the  water,  and  lead,  zinc,  cobalt  and  nickel  in  the 
marine  organisms;  and  since  there  are  in  sea-water  small 
amounts  of  hydrogen  sulphide,  Bischof  considers  the  deposi- 
tion of  metallic  sulphides  from  the  sea  to  have  been  possible. 
He  observes  (op.  cit.,  p.  432)  that  the  occurrence  of  metallic 
sulphides  in  sedimentary  rocks,  such  as  that  of  copper  and  sil- 
ver sulphides  in  Kupferschiefer,  or  that  of  lead  sulphide  in 
Buntsandstein,  may  be  thus  explained ;  and  even  indulges  (p. 
836)  in  the  following  teleological  conclusion : 

' '  Since  it  cannot  be  doubted  that  the  rivers  flowing  into  the  ocean  bring  with 
them  metallic  salts,  though  in  very  dilute  solution,  it  seems  a  wise  arrangement  that 
in  the  hydrogen  sulphide  of  sea-water  a  precipitant  is  presented  to  throw  down  the 
smallest  minima,  and  thus  to  prevent  the  gradual  accumulation  of  substances  so 
injurious  to  animal  life." 

Of  the  various  metals  dissolved  in  sea-water,  iron  is  least 
injurious  to  animal  life.  Indeed,  animal  life  assists,  in  the  so- 
called  lake-ores,  the  segregation  of  this  metal.  Moreover,  the 
precipitation  of  ferrous  and  ferric  oxides  from  concentrated 
solutions  is  probable,  so  that  a  precipitation  of  iron-ores  di- 
rectly from  sea-water  seems  to  be  established  as  a  possible  ori- 
gin for  some  iron-ore  beds. 

But  the  conveyance  of  metallic  salts  by  rivers  to  the  ocean 
and  the  formation  of  hydrogen  sulphide  in  sea-water  are  un- 
questionably continuous ;  and  the  precipitation  of  metallic 
sulphides  must,  therefore,  have  taken  place  uniformly  in  all 
sediments  and  precipitates  of  the  ocean ;  whereas,  we  find  the 
ore-beds  in  fact  only  in  certain  strata.  If  these  are  to  be  thus 
explained,  we  must  assume  that  the  ocean  was  at  certain  periods 
much  more  strongly  impregnated  with  metallic  salts — a  scarcely 

*  G.  Bischof,  Chem.  u.  Phys.  Geologic,  vol.  i.,  Bonn,  1843,  pp.  445-447. 


122  THE    GENESIS    OF    ORE-DEPOSITS. 

tenable  hypothesis  as  applied  to  the  mighty  deep, — or  we  must 
suppose  with  Carnall,  as  H.  Hoefer  has  recently  done,*  a  sub- 
sequent re-deposition  of  the  primitive  metallic  salts,  contained 
in  minute  quantities  in  the  sea-deposits — in  other  words,  their 
solution  and  re-precipitation  at  certain  horizons.  Hoefer  cites 
the  lead-  and  zinc-deposits  of  Upper  Silesia  and  other  districts, 
which  occur  in  marine  Triassic  limestones.  He  assumes  the 
maintenance  of  uniform  horizons  by  these  deposits  to  be  demon- 
strated, but  points  out  that  some  of  these  horizons  were  already 
ore-bearing  when  first  formed. 

In  short,  a  number  of  investigators  have  adopted  the  hy- 
pothesis of  an  original  ore-deposition  from  the  ocean,  without 
giving  any  other  reason  than  the  observed  relations  of  stratifi- 
cation. Yet,  in  a  considerable  experience  with  ore-deposits  in 
marine  limestones,  I  have  never  been  able  to  find  genuine  ore- 
beds  among  them,  but  always  only  ores  of  subsequent  intro- 
duction; so  that  I  feel  warranted  in  believing  that  such  ore- 
beds  proper  do  not  exist. 

As  to  the  primitive  ore  contained  in  marine  sediments  and 
precipitates,  innumerable  chemical  analyses,  especially  of  lime- 
stone, have  failed  to  show  the  metallic  traces  which,  according 
to  the  above  hypothesis,  should  be  present.  For  this  reason, 
as  I  have  already  observed,  even  Sandberger  did  not  venture 
to  derive  the  metals  from  the  limestone,  preferring,  for  in- 
stance, at  Raibl,  to  look  to  the  overlying  slates. 

The  maintenance  of  certain  ore-bearing  horizons  was  set  up 
by  A.  von  Groddeck,  to  render  more  plausible  the  notion  of  a 
direct  deposition  from  the  ocean ;  but  I  do  not  believe  it  pos- 
sible to  prove  such  an  identity  of  horizon  for  different  ore- 
deposits.  Similar  ores  and  stratigraphical  conditions  are  not 
confined  to  the  Trias.  On  the  Rhine,  in  England  and  in 
America  they  occur  at  much  lower  horizons  in  the  Palaeozoic 
rocks.  Even  in  Carinthia  the  ore-bearing  limestones  of  the 
richest  deposits  do  not  occupy  the  same  horizon.  That  of  the 
Raibl  slate  is  very  different  from  that  of  the  Bleiberg  slate 
(carrying  Ammonites  aori),  and  the  deposits  in  these  localities  are 
by  no  means  beds,  but,  as  I  have  shown,  channels  in  the  lime- 
stone, filled  with  ore. 

*  "  Die  Entstehung  der  Blei-,  Zinc-  u.  Eisenlagerst.  in  Oberschlesien."— Oesterr. 
Zeitsch.f.  Berg.  u.  H -wesen,  1893,  xli.,  p.  82. 


THE    GENESIS    OF    ORE-DEPOSITS.  123 

Ore-Deposition  in  Fresh  Water. — The  demonstration  of  direct 
ore-deposition  in  fresh- water  strata  encounters  the  same  diffi- 
culties, though  it  may  be  supported  by  the  same  chemical 
speculations.  Here  the  hypothesis  is  favored  by  the  analogy  - 
of  the  lakes  of  regions  without  drainage  to  the  sea,  in  which 
the  salts  brought  in  by  rivers  are  necessarily  concentrated  by 
evaporation.  But  since  organic  life  is  restricted  in  these  salt 
lakes  to  a  few  animal  species,  the  analogy  can  have  but  a  limited 
application.  Moreover,  it  would  be  necessary  to  suppose  cata- 
clysmic changes,  like  the  interposition  of  a  period  of  no  drain- 
age in  the  midst  of  an  epoch  of  fresh-water  sedimentation. 

Without  the  assumption  of  such  cataclysms,  I  do  not  believe 
that  the  Mannsfeld  K^ferschiefer,  in  which  the  organic  (fish) 
remains  can  be  traced  continuously  from  foot-  to  hanging-wall, 
could  be  explained  in  this  way.  It  deserves  mention,  that  some 
of  the  earlier  geologists,  like  Freiesleben,  accepted  the  some- 
times contorted  attitudes  of  the  Palceoniscus  in  the  Kupferschiefer 
as  a  proof  of  contemporaneous  ore-depositions,  and  alleged  that 
these  fishes  had  been  thrown  into  violent  contortions  by  the 
copper-solution,  in  which  condition  they  died  and  were  buried 
in  the  sediment.  The  naivete  of  this  diagnosis  (which,  never- 
theless, some  modern  writers  have  not  hesitated  to  repeat)  is 
evident.  Contorted  fish-remains  occur  in  other  formations  out- 
side of  the  Kupferschiefer,  and  clearly  show  the  advanced  state 
of  decomposition  in  which  the  bodies  reached  the  sediments. 

The  Kupferschiefer  of  Mannsfeld. — The  Mannsfeld  Kupfer- 
schiefer, as  is  well  known,  is  a  thin  bed  of  bituminous  slate, 
lying  between  the  Permian  sandstone  below,  and  the  marine 
member  of  the  same  formation,  the  Zechstein,  above,  and  con- 
taining sulphides  of  copper,  silver,  lead,  zinc,  antimony,  mer- 
cury, nickel  and  cobalt.  The  copper  amounts  to  20  to  30  kilo- 
grams (44  to  66  pounds),  and  the  silver  to  125  to  150  grammes 
(4  to  5  ounces,  Troy)  per  metric  ton  of  2204  pounds.  In  pol- 
ished sections,  the  ore  can  be  seen  in  thin  leaves  lying  be- 
tween laminae  of  slate,  and  often  accompanied  by  gypsum. 
But  the  same  ores  occur  in  scattered  bunches  in  the  sandstone 
below,  and  small  bodies  of  redruthite  are  found  in  the  lime- 
stone above.*  This  circumstance  alone,  that  ore  occurs  also 

*  See  Groddeck's  Erzlagerstcitten,  |  58,  and  Cotta's  Manual,  \  50. 


124  THE    GENESIS    OF    ORE-DEPOSITS. 

in  the  marine  limestone,  above  the  fresh-water  Kupferschiefer, 
is  unfavorable  to  the  contemporaneous  origin  of  ore  and  rock. 

Kupferschiefer  in  Thuringia  and  Bohemia. — The  same  bitu- 
minous slate  occurs  in  the  Thuringian  forest  on  the  south  slope 
of  the  Hartz,  and  in  other  points  a  considerable  distance  away. 
It  must  therefore  have  been  deposited  in  a  large  basin.  But 
it  is  a  question,  whether  it  anywhere  carries  ore  and  deserves 
the  name  of  Kupferschiefer. 

In  KE.  Bohemia,  the  same  Permian  slate,  with  almost  the 
same  fossils,  is  widely  distributed,  but  without  the  marine 
member  which  covers  it  in  Germany.  The  Permian  of  Bo- 
hemia carries  copper-ores  in  many  places ;  and  in  one  locality, 
namely,  at  Hermannseifen,  these  ores  occur  in  the  bitumin- 
ous slate,  which  might  properly  here  be  called  Kupferschiefer. 
I  had  opportunity  in  1858  to  examine  the  mines.  The  richness 
in  metal  was  not  unsatisfactory ;  but  there  was  much  complaint 
of  the  numerous  faults  which  seriously  enhanced  the  difficulty 
of  mining. 

Precisely  the  same  difficulty  exists  at  Mannsfeld  and  in  the 
Thuringian  forest,  as  Gotta  (op.  cit.,  §50)  reports  in  part  as 
follows  : 

"The  fault- fissures  themselves  are,  however,  rarely  ore-bearing,  yet  often  seem 
nevertheless  to  have  influenced  the  ore-bearing  character  of  the  strata  traversed 
by  them.  This  influence  is  shown  in  the  increase  or  diminution  of  the  propor- 
tions of  ore,  not  only  in  the  immediate  neighborhood,  but  sometimes  also  for  a 
considerable  distance,  even  as  far  as  the  next  master-fault.  It  is  shown  also  in 
the  transfer  of  the  metallic  contents  from  one  stratum  to  another." 

This  and  other  observations  concerning  the  influence  of  the 
faults  upon  the  ore-distribution  bear  decidedly  against  the  con- 
temporaneity of  the  ore-deposits,  and  in  favor  of  a  later  intro- 
duction of  ore  through  the  fault-fissures. 

But  this  conclusion  becomes  much  clearer  upon  a  consider- 
ation of  the  remaining  occurrences.  Thus,  according  to  Cotta 
(op.  cit.,  §  39),  the  Kupferschiefer  at  the  edge  of  the  Thuringian 
forest  is  not  so  rich  in  ore  as  on  the  southern  border  of  the 
Hartz.  More  important  than  the  copper-slate  itself  are  the 
fault-fissures  which  traverse  the  whole  group  of  strata,  but 
only  carry  ore  in  certain  zones  in  which  they  intersect  certain 
strata — the  Kupferschiefer  among  them.  "  Strange  to  say," 
observes  Cotta,  "  near  Camsdorf  it  is  almost  exclusively  where 


THE    GENESIS    OF    ORE-DEPOSITS.  125 

the  Kupferschiefer  has  suffered  such  disturbances  that  it  is  rich 
enough  to  repay  mining."  In  speaking  of  Riegelsdorf  he  says, 
"  The  cobalt-ores  have  in  some  cases  made  their  way  from  the 
veins  into  the  country-rock." 

Westphalia. — At  Stadtberg  (op.  tit.,  p.  76),  in  Westphalia, 
there  are  even  several  copper-bearing  strata,  and  these  are  cut 
by  copper-bearing  veins.  At  Bieber,  veins  traverse  the  whole 
group  of  strata  into  the  underlying  mica-slate,  and  "  the  irreg- 
ularly distributed  ore  occurs,  strange  to  say,  chiefly  interleaved 
in  the  mica-slate,  and  not,  as  in  the  Hartz  and  the  Thuringian 
forest,  in  the  horizon  of  the  Kupferschiefer  ;  while,  on  the  other 
hand,  the  impregnations  from  the  veins  have  penetrated  chiefly 
the  bituminous  marly  slate." 

In  consideration  of  the  expressions  partly  quoted  verbatim 
above,  it  is  difficult  to  see  how  there  can  be  any  doubt  of  the 
secondary  nature  of  the  ore-deposits  in  the  Kupferschiefer 
throughout.  Yet  Groddeck*  has  reproved  me  for  coming  to 
this  conclusion.  He  says  himself  f  expressly  (evidently  having 
in  mind  the  typical  Mannsfeld  occurrence)  : 

"  The  ores  were  laid  down  contemporaneously  with  the  slime-deposit,  the  bitu- 
minous marly  slate  as  the  ore- matrix."  .  .  .  .  "It  is  entirely  impossible  that  the 
ores  could  have  entered  the  bed  somehow  from  the  fissures,  at  a  later  period,  after 
the  covering  of  the  marly  slate  with  more  recent  rocks.  If  we  assume  that  the 
ore-solutions  were  introduced  through  the  fissure  faulting  the  bed,  it  remains  in- 
conceivable why  the  filling  of  metallic  sulphides,  through  a  field  of  many  square 
miles,  should  be  uniformly  and  exclusively  confined  to  the  stratum  of  marly  slate, 
about  ^  meter  (19.5  inches)  thick,  and  should  not  also  occur  more  or  less  near  the 
fissures  in  the  strata  above  and  below,  there  being  in  these  no  lack  of  carbonates 
and  bituminous  constituents,  available  as  precipitants  of  the  solutions — the  Stink- 
schiefer,  for  instance,  lying  not  far  above  the  Kupferschiefer,  being  rich  in  such 
substances. ' ' 

Groddeck  here  overlooked  the  principle,  \  elsewhere  urged 
by  him,  that  a  single  link  in  a  whole  chain  of  phenomena 
should  not  be  exclusively  considered.  He  contemplated  only 
the  special  development  at  Mannsfeld ;  assumed,  moreover,  sim- 
ilar developments  for  many  square  miles,  which  show  in  fact 
many  variations,  and  did  not  take  into  account  the  circum- 
stance that  when  the  Kupferschiefer  is  not  cut  by  fault-fissures, 
it  is  also  not  valuable  for  mining.  Finally,  he  was  unac- 

*  "Bemerk.  zur  Classification  d.  Lagerstatten,"  B.  u.  H.  Ztg.,  1885. 
f  Erzlagerstattenlehre,  $  142. 


126  THE    GENESIS    OF    ORE-DEPOSITS. 

quainted  with  the  theoretically  important  occurrence  of  the 
Kupferschiefer  in  Bohemia.  The  contemporaneous  origin  of  the 
ore  and  rock  at  Mannsfeld  was  with  him,  so  to  speak,  a  dogma, 
as  may  he  perceived  in  some  of  his  expressions  (op.  tit.,  p.  302) : 

"The  local  ore-bearing  character  of  the  foot-  and  hanging-walls  of  the  Kupfer- 
schiefer-bed  is  no  proof  to  the  contrary,  for  it  is  always  confined  to  the  immediate 
neighborhood  of  the  bed."  (?) 

"Into  the  sea,  rich  in  fishes  and  plants,  from  which  the  marly  slate  was  de- 
posited, flowed  abundant  metallic  solutions,  which  killed  the  organisms  and  were 
themselves  reduced  by  the  products  of  decay."  (?) 

The  first  of  these  propositions  becomes  logical  if  it  is  simply 
reversed  in  sense ;  and  the  bold  hypothesis  of  the  second  indi- 
cates a  doubt  which  the  author  is  seeking  in  this  way  to  set  at 
rest.  His  statement  (p.  302) : 

"  It  is  not  to  be  doubted  that  metallic  sulphides  may  be  formed  at  the  earth's 
surface,  under  ordinary  pressure  and  temperature,  beneath  a  water-covering 
which  excludes  the  air," 

is  quite  correct ;  but  when  he  adds : 

"And  there  is  therefore  nothing  to  prevent  the  belief  that  sulphuretted  ores 
could  be  precipitated  at  the  same  time  with  the  deposition  of  sedimentary  rocks," 

it  is  necessary  to  add,  "provided  the  metallic  salts  were  present 
in  the  sea-basin." 

This  is,  indeed,  the  center  of  gravity  of  the  whole  question ; 
and,  as  I  have  shown,  the  proposition  presents  an  improba- 
bility. 

Various  other  peculiarities  of  individual  ore-occurrences  are 
cited  in  favor  of  the  theory  of  contemporaneous  origin;  but 
all  of  them,  when  impartially  weighed,  are  equally  consistent 
with  a  different  genetic  explanation,  and  fail  to  be  as  signifi- 
cant as  the  Mannsfeld  type  for  the  theory  in  question. 

The  Copper-Sandstones  of  Bohemia. — In  Bohemia  and  on  the 
west  slope  of  the  Urals,  the  copper-ores  of  the  Permian  strata 
occupy  by  no  means  a  continuous  horizon,  but  occur  as  im- 
pregnations in  different  beds,  beside,  above,  or  below  one  an- 
other. There  are  here,  as  in  the  German  Kupferschiefer  mines, 
fault-fissures  which  may  have  served  as  ore-conduits ;  and  in 
these  regions  the  notion  of  a  primary  sedimentary  origin  of  the 
ores  has  not  been  so  often  suggested.  At  some  places  in  Bo- 


THE    GENESIS    OF    ORE-DEPOSITS.  127 

hernia,  as,  for   instance,  at   Starkenbach,  melaphyres  appear 
above  the  ore-beds. 

In  almost  all  these,  as  in  many  of  the  German  deposits,  the 
copper  sulphides,  especially  redruthite,  occur  in  the  neighbor- 
hood of  plant-remains ;  and  oxidized  copper-ores  predominate, 
as  a  rule,  in  the  ore-beds  in  sandstone. 

Not  only  Permian,  but  also  Triassic  and  still  more  recent 
sandstones,  exhibit  analogous  deposits,  containing  lead,  silver, 
and  antimony,  as  well  as  copper.  At  Boleo,  in  Lower  Cali- 
fornia, such  an  ore-deposit  is  known  in  Tertiary  strata.  The 
range  of  illustrations,  therefore,  is  an  extensive  one.  I  can 
mention  but  a  few. 

St.  Avoid. — Concerning  the  copper-ores  in  the  Triassic  sand- 
stone of  St.  Avoid  and  Wallerfangen,  Groddeck  gives  (p.  90)  a 
brief  description,  based  on  an  article  by  C.  Simon.*  The 
sporadic  ores  are  most  abundant  in  the  vicinity  of  fault-fis- 
sures ;  but  only  single  strata  are  rich,  while  other  porous  layers 
near  by  are  barren  of  ore.  The  ores  extend  in  zones,  inde- 
pendent of  the  course  of  the  fissures,  which  they  often  even 
cross  at  right-angles.  These  two  features  are  said  to  prove  the 
contemporaneous  origin  of  the  ore  and  rock,  "  since  the  en- 
richment of  a  zone  where  it  is  cut  by  the  fissures  can  be  simply 
explained  by  the  leaching-out  of  ores  in  higher  strata,  and  their 
re-deposition  in  or  near  the  fissure."  I  must  confess  that  this 
explanation  is  not  satisfactory  to  me.  Figs.  80  and  81  illus- 
trate the  situation. 

At  Bleiberg,  in  St.  Avoid,  concretions  of  galena,  of  pea-size, 
occur  in  the  sandstone ;  and  below  the  same  layer  considerable 
masses  of  solid  galena  are  encountered. 

The  Lead-Deposit  of  Mechermch,  near  Commern.-f — This  de- 
posit has  a  special  interest  in  this  connection,  since  it  consists 
of  sandstone  of  considerable  thickness,  somewhat  porous,  and 
impregnated  with  small  concretions  of  galena  (Knoten\  which 
have  often  been  considered  as  contemporaneous  in  deposition 

*  Berg.  u.  H.  Ztg. ,  1866,  p.  412. 

f  Baur,  "  Das  Vorkommen  von  Bleierzen  am  Bleiberge  bei  Commern,"  Esch- 
weiler  Pumpe,  1859. 

F.  W.  Huperts,  Der  Bergbau  u.  Hilttenbetrieb  des  Mechernicher  Bergw.  akt.  Ve- 
reins,  Koln,  1883. 

Ellsworth  Daggett,  "The  Lead  and  Silver  Works  of  the  Mechernich  Mining 
Company,"  E.  and  M.  J.,  xxiii. 


128  THE    GENESIS    OF    ORE-DEPOSITS. 

with  the  rock.  The  district,  situated  on  the  north  edge  of  the 
Eifel  Mountains,  embraces  a  zone  about  7  kilometers  (4J  m.) 
long,  through  Call,  Keldenick,  Mechernich  and  Strempt.  Al- 
ready in  the  Roman  period,  at  the  Tanz  Mountain,  near  Kel- 
denick, mining  was  done  upon  galena  veins  in  the  Devonian 
limestone,  which  is  overlain  by  the  sandstone  and  conglomerate 
of  the  variegated  sandstone  formation.  The  conglomerate  cov- 
ering the  sandstone  has  the  name  of  Wackendeckd,  and  some- 
times carries  ore,  the  cement  between  its  pebbles  being  trav- 
ersed by  galena  and  oxidized  products,  especially  cerussite, 
which  were  formerly  mined. 

It  is  at  present  the  sandstone,  impregnated  with  galena  con- 
cretions (Knoten)  to  the  extent  of  5  to  30  kg.  (0.5  to  3  per 
cent.)  of  lead,  and  1  to  6  grammes  (0.03  to  0.18  oz.  Troy)  silver 
per  metric  ton  of  2204  pounds,  which  is  the  principal  basis  of 
an  extensive  mining  industry. 

The  thickness  of  this  Knotensandstein,  the  number  of  its  in- 
tercalated conglomerate  layers,  and  the  richness  in  ore  of  each 
stratum  vary  greatly,  as  do  also  the  number,  direction  and  man- 
ner of  throw  of  the  fault-fissures  by  which  it  is  traversed.  Fig. 
82,  representing  the  stratigraphy  SW.  of  the  boundary  of  the 
mining  grant  at  Meinerzhagen,  shows  the  irregularity  of  the 
displacements.  Within  the  grant,  the  several  TTnofen-layers  are 
united  into  a  single  bed,  about  22  meters  (72  feet)  thick,  sep- 
arated by  a  conglomerate  layer  from  the  Devonian  rocks  below, 
and  overlain  by  another  conglomerate,  the  so-called  Wacken- 
deckel,  above  which  is  the  barren  red  sandstone.  In  general 
terms,  there  lies  here  upon  an  impermeable  floor  a  pervious 
group  composed  of  sandstones  and  conglomerates,  overlain  by 
argillaceous  red  sandstone  and  loam. 

The  Knoten,  never  larger  than  peas,  exhibit,  when  prepared 
in  thin  sections  and  mounted  in  Canada  balsam,  crystalline  ag- 
gregates of  galena,  in  which  the  crystal-faces  are  turned  out- 
wards, away  from  the  center ;  that  is,  they  are  by  no  means 
composed  of  spherical  masses,  as  they  seem  to  the  naked  eye 
to  be,  when  examined  as  they  come  from  the  crumbly  rock. 
Thei^  distribution  in  the  sandstone  generally  follows  the  bed- 
ding; but  in  the  neighborhood  of  the  cross-faults  I  observed 
an  accumulation  of  Knoten  in  zones  parallel  to  these  steep  fis- 
sures. Moreover,  I  found  occasionally  in  the  fissures  them- 


THE    GENESIS    OF    ORE-DEPOSITS.  129 

selves  threads  of  galena  and  pyrite ;  and  hence  I  do  not  doubt 
that  the  ore-deposition  here  was  secondary,  and  proceeded  from 
the  fissures.  To  gain  a  clear  view  of  this  question,  it  is  neces- 
sary to  include  the  ore-occurrence  in  the  conglomerates,  where, 
as  already  observed,  it  impregnates  the  material  cementing  the 
pebbles,  and  also  the  nearest  ore-occurrence  in  the  Devonian 
limestone,  where  it  appears  in  fissure-veins. 

In  my  opinion,  the  loose,  pervious  sandstone,  enclosed  be- 
tween less  permeable  strata,  and  cut  by  many  fault-fissures, 
was  impregnated  by  ascending  springs,  which  employed  it  as  a 
path  in  their  circulation;  but  it  cannot  be  determined  what 
constituted  the  centers  around  which  the  galena  concretions 
are  formed.  May  it  have  been  minute  particles  of  feldspar, 
such  as  are  still  occasionally  visible;  or  was  it  organic  sub- 
stances, which  have  now  entirely  disappeared  ? 

Freihung. — Perhaps  additional  hints  may  be  furnished  by 
the  mines  of  Freihung  in  the  Bavarian  Upper  Palatinate, 
which  Gotta  considers  analogous  to  those  of  Mechernich. 
Here  galena  and  cerussite  impregnate  the  Keuper  sandstone, 
the  steep  dip  of  which  they  share.  At  the  Nuremberg  Expo- 
sition of  1882,  maps,  ore-  and  rock-specimens  from  the  mines 
of  the  Bavarian  Lead-Mining  Co.  were  exhibited.  Fig.  83  is 
a  section  through  the  Vesuvius  mine.  I  was  struck  with  nu- 
merous specimens  of  tree-stems  changed  to  galena ;  and, 
coming  subsequently  into  possession  of  such  a  specimen,  I 
had  a  polished  section  prepared  from  it.  The  pieces  of  these 
stems  exhibited  are  about  20  centimeters  (8  inches)  long,  and 
elliptical  in  sections,  say  5  to  7  by  10  to  15  centimeters  (2  to  3 
by  4  to  6  inches).  The  fiber  and  the  annual  rings  could  be 
recognized  on  the  surfaces  of  fracture,  but  were  extremely 
plain  in  the  polished  section.  Indeed,  they  were  indicated  by 
the  cleavage  of  the  specimens.  I  have  thin  slivers,  2  to  4  mm. 
(0.08  to  0.16  inch)  in  diameter  and  several  centimeters  long, 
representing  the  fibers  of  the  original  wood.  The  former 
bark  is  replaced  by  a  zone  of  first  pyrite,  and  then  quartz 
grains  cemented  with  pyrite.  I  do  not  know  that  the  determi- 
nation of  the  species  of  the  wood  has  been  attempted,  but  I 
think  it  should  be  approximately  practicable.  Fig.  84  is  a 
diagram  of  the  section  of  such  a  stem  altered  to  galena. 

Certainly  we  have  here  another  instance  showing  that  the 


130  THE    GENESIS    OF    ORE-DEPOSITS. 

organic  substance  attracted  metallic  solutions  and  reduced  them 
to  sulphides,  and  this  under  conditions  similar  to  those  of 
Mechernich.  The  latter  occurrence  may,  therefore,  be  most 
simply  explained  by  the  hypothesis  of  an  organic  substance, 
distributed  through  the  rock,  which  reduced  the  circulating 
mineral  solutions  and  occasioned  the  formation  of  the  concre- 
tions (Knoteri). 

Silver  Reef. — Accustomed  as  we  are  to  find  silver  associated 
with  lead-ores,  we  are  surprised  by  the  occurrence,  in  the  Silver 
Reef  district  of  Utah,  in  probably  Triassic  sandstones,  of  silver 
accompanied  by  copper.  So  far  as  can  be  gathered  from  the 
various  descriptions  at  hand,*  there  occur  here  two  beds  (the 
outcrops  of  which  are  called  "  reefs  ")  which  carry  silver,  either 
exclusively  or  with  a  little  copper — the  former  usually  as  a 
chloride,  but  sometimes  native ;  and  the  latter  in  the  ordinary 
oxidized  ores.  It  may  be  reasonably  inferred  that  the  deposit 
has  been  thus  far  exposed  in  its  upper,  chloridized  and  oxi- 
dized zones ;  and  that  in  depth  it  would  be  found  to  contain 
sulphide-ores.  "Whether  such  depth  has  been  reached  by  the 
miners  I  do  not  know. 

The  beds  consist  of  red  and  gray  argillaceous  sandstones  and 
arenaceous  clay-slates,  between  the  laminse  and  in  the  cross- 
joints  of  which  the  ores  occur,  being  the  more  concentrated, 
the  more  highly  fissured  the  condition  of  the  rock.  Although 
traces  of  silver  are  found  throughout  the  bed,  the  pay-ore  is 
confined  to  separate  chimneys  or  channels,  which  descend  on 
the  true  dip,  or  pitch  obliquely  to  it.  The  richest  bodies  are 
said  (Rolker,  L  c.,  p.  25)  to  be  most  frequently  found  above  a 
certain  thin,  very  clayey,  sandstone  stratum.  Yery  often,  but 
not  always,  the  silver-ore  is  accompanied  by  carbonized  vege- 
tation, such  as  trunks  and  stems  of  trees,  and  reed-like  plant- 
remains,  which  are  covered  and  impregnated  with  horn-silver. 
The  copper-  and  silver-ores,  while  occurring  to  a  certain  degree 
in  association,  seem  to  exclude  one  another,  and  are  seldom 
found  in  actual  mixture. 

*  "The  Silver  Keef  District,  Southern  Utah"  (by  K.  P.  Eothwell  or  Thomas 
Couch?),  Eng.  and  M.  Jour.,  xxix.,  pp.  25,  45,  59,  79,  351. 

C.  M.  Kolker,  "The  Silver-Sandstone  District  of  Utah,"  Trans.  A.  L  M.  E., 
ix.,  21. 

J.  S.  Newberry,  "Report  of  the  Stormont  -Silver  Mining  Co.,"  E.  and  M.  J., 
xxx.,  p.  269. 


THE    GENESIS    OF    ORE-DEPOSITS.  131 

The  same  sandstone  which  here  carries  ore  is  said  to  be  rep- 
resented in  the  plateau  cut  by  the  Colorado  river ;  but  there 
the  strata  are  horizontal  and  undisturbed,  whereas  in  the  ore- 
district  they  dip  rather  steeply,  are  much  disturbed,  and  are  in 
many  places  covered  with  eruptive  rocks,  including  basalt.  This 
neighborhood  to  eruptives  renders  it  probable  that  here,  as  in 
so  many  other  places  in  Western  America,  the  ores  have  been 
introduced  by  the  mineral  springs  which  usually  follow  erup- 
tive activity.  Rothwell,  Couch,  and  Rolker  are  of  this  opinion ; 
whereas,  dewberry  is  inclined  to  suppose  a  contemporaneous 
origin  of  ores  and  rock.  The  principal  arguments  for  his  view 
are,  the  alleged  great  area  of  silver-bearing  Triassic  strata  in 
that  region ;  and  the  circumstance  that  the  richest  bedded  and 
lenticular  ore-bodies  are  enclosed  in  almost  impermeable  slate- 
clays,  which  would  not  have  permitted  a  subsequent  entrance 
of  the  mineral  solutions.  Neither  of  these  statements  disproves 
the  secondary  origin  of  the  ores.  They  could  have  been  de- 
posited in  any  given  way  on  a  large  scale,  as  well  as  a  small  one ; 
and  that  the  almost  impermeable  slate-clays  did  not  prevent  the 
entrance  of  solutions  is  proved  by  the  subsequent  alteration  of 
the  original  filling  to  chlorides  and  oxides.* 

Moreover,  the  deposits  are  not  regular  strata,  but  chimneys 
and  channels  in  parts  of  strata,  and  this  character,  which  they 
possess  in  common  with  so  many  other  deposits,  should  be  de- 
cisive in  favor  of  their  secondary  origin — a  conclusion  which, 
in  my  opinion,  is  always  reached  when  observations  are  not  con- 
fined to  single  localities,  but  extended  over  whole  series  of  anal- 
ogous phenomena. 

Copper-Deposits  of  New  Mexico  and  Arizona. — Traces  of  sim- 
ilar ore-distribution  in  sandstones  seem  to  be  not  infrequent  in 
the  American  West.  Thus  F.  M.  F.  Cazinf  says  of  the  copper- 
ores  of  the  probably  Triassic  sandstones  of  the  Nacimiento 
mountains  in  ET.  W.  New  Mexico,  which  J.  S.  dewberry  had 
described  in  1860 : 

' '  The  ore  occurs  nearly  exclusively  as  the  petrefaction  of  the  leaves,  stones,  limbs 
and  trunks  of  palms.     Frequently  the  ore  is  coated  with  a  film  of  jet  or  coal.     It 

*  Compare  F.  M.  F.  Cazin,  "The  Origin  of  Copper-  and  Silver-Ores  in  Triassic 
Sandrock,"  E.  and  M.  J.,  xxx.,  p.  381. 

f  "New  Mexico  vs.  Lake  Superior  as  a  Copper-Producer."— j£.  and  M.  J., 
xxx.,  pp.  87,  108. 

9 


132  THE    GENESIS    OF    ORE-DEPOSITS. 

is  always  easily  separated  from  the  rock.  The  ore  is  predominantly  erubesite, 
copper-glance  and  melaconite,  and  it  appears  to  be  distributed  all  over  the  mass- 
ive stratum,  but  is  more  densely  collected  on  seams  and  cleavages,  in  some  instances 
forming  a  single  layer  of  petrified  parts  of  palm-wood." 

This  occurrence,  which  is  analogous  to  those  in  Bohemia  and 
in  the  province  of  Perm,  was  declared  to  possess  great  economic 
importance.  Its  later  developments  are  not  known  to  me. 

"W.  P.  Blake*  has  described  an  analogous  occurrence  in  the 
sandstones  and  conglomerates  overlying  the  granites  in  Copper 
Basin,  Yavapai  county,  Arizona,  where  the  copper-ores  are 
found  unconnected  with  any  organic  substances.  In  the  under- 
lying granite,  however,  there  are  fissures  filled  with  copper-ores. 
He  thinks  it  probable  that  copper  sulphides  circulating  in  the 
highly  permeable  sandstone  were  precipitated  as  carbonate  by 
carbonate  of  soda,  while  the  resulting  sulphate  of  soda  escaped 
in  solution,  to  be  concentrated  by  evaporation,  forming  deposits 
of  thenardite,  which  is  common  in  Arizona. 

Lower  California. — At  Boleo,  opposite  Guaymas,  on  the  pen- 
insula of  Lower  California,  E.  Fuchsf  has  described  a  remark- 
able deposit  of  copper-ores  in  Tertiary  sandstones,  conglomer- 
ates and  tufas,  which  must  be  mentioned  under  this  head.  The 
east  slope  of  the  (mostly  eruptive)  mountain  range  extending 
through  the  peninsula  is  a  plateau,  gently  descending  towards 
the  Gulf  of  California,  and  cut  by  precipitous  canons.  It  is 
formed  of  strata  containing  characteristic  Miocene  fossils. 
Tufas  decidedly  predominate,  and  the  series  contains  three  or 
four  copper-bearing  beds,  covering  a  large  area,  and  out-crop- 
ping in  many  places  in  the  canons.  These  lie  immediately 
upon  conglomerates  of  pebbles  of  eruptive  rock  (different  and 
characteristic  for  each  horizon)  and  are  overlain  by  clayey  tufas. 
The  whole  is  traversed  by  several  fissures,  of  which  the  largest 
and  most  important  is  a  fault-fissure,  occurring  at  the  western 
border  of  the  district  and  striking  about  parallel  with  the  sea- 
shore. 

In  the  ore-beds  above  the  ground-water  level,  disseminated 
oxidized  ores  prevail,  such  as  black  oxide  of  copper,  and  the 

*  "  The  Copper-Deposits  of  Copper  Basin,  Arizona,  and  their  Origin." — Trans. 
A.  I.  M.  E.,  xvii.,  479. 

f  "  Note  sur  les  Gisements  de  Cuivre  du  Boleo. "  —Assoc.  Francaise  pour  V  ^van- 
cement  des  Sciences,  1885. 


THE    GENESIS    OF    ORE-DEPOSITS.  133 

protoxide,  with  atacamite  (CuCl  4-  3  CuO  +  3H20),  azurite, 
malachite  and  chrysocolla,  with  crednerite  (2  Mn203,  3  CuO). 
In  the  second  ore-bed  (counting  downwards)  there  are  peculiar 
globular  concretions,  like  oolites,  of  copper  oxide  and  carbon- 
ate, sometimes  several  centimeters  in  diameter,  which  are  lo- 
cally called  boleos,  whence  the  name  of  the  district.  Though 
greatly  interested  in  this  type  of  ore,  I  have  never  succeeded 
in  getting  specimens,  and  am  unable  to  form  from  the  hasty 
description  of  Fuchs  a  clear  conception  as  to  its  genesis. 

The  third  bed  lies  in  part  below  the  ground-water  level,  and 
contains,  in  addition  to  the  foregoing  minerals,  the  copper  sul- 
phides chalcosine  (Cu2S)  and  covelline  (CuS). 

The  ore-beds  are  composed  of  tufa  (the  slime,  according  to 
Fuchs,  of  volcanic  eruptions),  in  which  ores  in  disseminated 
spots  and  veinlets  ("  sous  forme  de  mouche  ou  de  veinules  ")  as  well 
as  globular  concretions,  are  irregularly  distributed,  with  a  vis- 
ible tendency  to  concentrate  towards  the  bottom  of  the  bed, 
where  they  form  a  compact  ore-layer,  15  to  25  centimeters  (6 
to  10  inches)  thick. 

With  regard  to  genetic  questions,  we  must  bear  in  mind  that 
the  fossils  found  in  these  strata  indicate  an  open  though  not 
very  deep  sea ;  it  is,  therefore,  impossible  to  assume  that  iron-, 
manganese-  and  copper-ores  were  dissolved  in  it,  and  were  pre- 
cipitated from  it  at  the  same  time  with  the  rock.  A  periodical 
metallic  precipitation,  three  or  four  times  repeated,  in  an  open 
marine  basin,  is  out  of  the  question ;  and  we  are  forced  in  this 
case,  even  more  strongly  than  elsewhere,  to  assume  a  secondary 
origin  for  the  ores.  The  data  necessary  for  its  explanation  are 
still  wanting,  but  can  undoubtedly  be  secured  by  the  further 
advance  of  mining  work.  E.  Fuchs  contented  himself  with 
pointing  out  the  after-effects  of  eruptive  processes,  and  did  not 
enter  upon  the  genetic  question.  Certainly  the  conglomerates 
underlying  the  ore-bed  must  have  played  an  important  part, 
representing,  very  likely,  the  channels  through  which  the  min- 
eral solutions  ascended,  to  be  reduced,  probably  by  the  presence 
of  organic  matter,  in  the  tufas  above. 

b.  Metasomatic  Deposits  in  Soluble  Rocks. 

A  metasomatic  replacement  of  the  original  rock  material  was 
clearly  proved  long  ago  for  some  instances — e.g.,  calamine-de- 


134  THE    GENESIS    OF    ORE-DEPOSITS. 

posits — while  in  other  cases,  where  proof  has  not  been  obtained, 
analogies  in  the  observed  circumstances  speak  for  such  an  origin. 
Parts  of  such  deposits,  it  is  true,  may  be  fillings  of  spaces  of 
dissolution,  rendered  unrecognizable,  as  such,  by  the  absence 
of  clearly  defined  crustification  in  the  ore-precipitates.  We  must 
accustom  ourselves  to  the  fact  that  for  many  deposits,  not  yet 
closely  enough  studied,  it  is  impossible  to  determine  positively 
the  mode  of  genesis,  and  we  must  often  choose  provisionally,  of 
the  two  modes  just  named,  the  one  which  appears  to  represent 
better  the  given  data. 

Calamine-Deposits. — The  calamine-deposits  of  Raibl  in  Car- 
inthia,  Wiesloch  in  Baden,  Yieille  Montague,  with  its  vicinity, 
in  Belgium  and  Germany,  and  other  places,  furnish,  in  the 
fossils  of  the  limestone  which  have  been  transformed  into  cala- 
mine,  the  clearest  proofs  of  a  metasomatic  replacement  of  the 
carbonate  of  lime  by  carbonates  and  silicates  of  zinc.  More- 
over, the  structure  and  form  of  the  ore-deposits  is  characteristic 
of  this  origin,  these  being  mostly  bodies  of  irregular  outline, 
with  portions  projecting  far  into  the  country-rock.  Often  the 
progress  of  the  replacement  can  be  traced.  Thus,  at  Raibl 
(Fig.  85),  in  places  where  the  process  has  started  from  seams, 
the  gradual  advance  from  the  seam  into  the  rock  may  be  ob- 
served ;  the  outermost  portions  being  relatively  the  most  recent, 
and  lying  against  a  peculiarly  uneven,  rough  surface  of  lime- 
stone. 

Sometimes  features  of  the  original  rock-structure  are  repeated 
in  calamine,  as,  for  instance,  the  cellular  structure  of  the  so- 
called  Hauchwacke  (the  cargneule  of  the  Swiss  geologists),  which 
consists  of  a  skeleton  of  thin,  smooth  lime-partitions,  from 
among  which  the  limestone  has  been  in  part  dissolved  away,  or 
left  only  in  separate  decomposed  splinters.  This  is  evidently  the 
result  of  a  very  complex  metamorphosis,  which  Groddeck  has 
observed  also  in  the  quicksilver-deposit  of  Avala  in  Servia. 
The  cell-walls,  which  represent  the  fillings  of  cracks  in  a  shat- 
tered  limestone,  have  been  subsequently  changed  to  calamine, 
and  covered  with  botryoidal  clusters  of  that  mineral  (Fig.  86). 

Calamine  is  frequently  formed  by  atmospheric  agencies  above 
the  ground-water  level,  and  is  a  frequent  accompaniment  of 
lead-  and  zinc-deposits  in  limestone. 

Space  does  not  permit  the  description  here  of  the  manifold 


THE    GENESIS    OF    ORE-DEPOSITS.  135 

deposits  in  Belgium,  Rhenish  Prussia,  Westphalia,  Upper 
Silesia,  Sardinia,  Algiers,  etc.,  which  are,  moreover,  not  known 
to  me  by  personal  observation.  The  text-books  of  Cotta,  Grod- 
deck  and  Phillips  give  some  account  of  them,  and  refer  to 
sources  of  more  detailed  information. 

Laurium. — It  is  only  in  recent  periods  that  the  features  of  the 
extensive  mining  region  of  Laurium  in  Greece,*  worked  two 
thousand  years  ago,  have  been  described.  Although  various 
kinds  of  deposits  are  represented,  most  of  them  belong  under 
the  present  head. 

In  the  Camaresa  district,  a  series  of  nearly  horizontal,  non- 
fossiliferous  limestones  and  crystalline  schists  is  cut  by  a  num- 
ber of  eruptive  dikes,  and  suddenly  assumes  on  the  ]STE.  a  steep 
dip,  probably  indicating  a  considerable  dislocation.  The  whole 
group  is  traversed  by  a  number  of  ore-veins,  which,  in  the 
schists,  are  often  rich  enough  to  pay  for  mining.  But  the  main 
mass  of  the  ores  lies  on  the  contact  between  limestone  and 
schist,  and  extends  into  the  former  in  separate  bodies  or  shoots. 
At  the  so-called  second  and  third  contacts,  the  bodies  have  a 
prevailing  funnel-shape  and  a  vertical  position.  Fig.  87,  an 
illustration  from  Huot,  shows  the  apexes  of  the  funnels  to  point 
on  one  contact  upward,  and  on  the  other  downward — but,  in 
either  case,  into  the  limestone,  according  as  it  overlies  or  under- 
lies the  schist.  The  first  form  may  be  explained  by  the  pres- 
sure of  the  ascending  solutions.  The  second,  as  shown  in  this 
figure,  is  perhaps  somewhat  ideally  sketched ;  at  least  the  sec- 
tions of  this  third  contact  given  by  Cordelia  show  ore-bodies 
following  the  contact-plane  itself. 

According  to  Fig  88  (also  from  Huot)  the  ore-bodies  are 
funnel-shaped  in  N".  to  S.  section,  but  from  E.  to  "W.  have  a 
flat  westward  pitch,  which  is  hard  to  explain  unless  it  repre- 
sents some  kinds  of  cleavage  parallel  to  the  dislocation  already 
mentioned.  Below  the  second  contact,  which  carries  chiefly 
lead,  there  are  (at  the  Jean  Baptiste  shaft,  for  instance,  accord- 
ing to  Cordelia)  great  masses  of  calamine,  the  secondary  origin 
of  which  from  zinc-blende  is  doubtful,  since  it  would  involve 
the  assumption  that  the  ground-water  zone  had  extended  to 

*  A.  Cordelia,  La  GrZce  sous  le  Rapport  Qeologique  et  Mineralogique,  Paris,  1878  ; 
and  Le  Laurium,  Marseilles,  1869.  A.  Huot,  Rapport  sur  les  Mines  du  Sumium, 
1880,  and  Memoires  de  la  Societe  des  Ing.  Civ.,  1876-78. 


136  THE    GENESIS    OF    ORE-DEPOSITS. 

this  depth.  As  to  the  present  subterranean  water-level,  I  find 
in  the  descriptions  at  hand  only  the  statement  that  the  region 
generally  is  very  dry,  and  that  the  ancients,  who  mined  to  the 
depth  of  120  meters  (394  feet),  had  no  water  to  hoist.  With 
regard  to  the  structure  of  the  galena-deposits,  I  may  say  that  I 
saw  in  the  exhibit  of  the  Cie.  Francaise  des  Mines  de  Laurium,  at 
the  Paris  Exposition  of  1867,  masses  of  galena,  blende  and 
pyrite  showing  distinct  stratification,  but  did  not  learn  from 
which  deposit  they  came. 

Which  of  the  various  eruptive  rocks  of  the  district  (eurite, 
porphyry,  diabase,  serpentine,  trachyte)  gave  occasion  for  the 
ascending  springs  which  brought  up  the  ore,  cannot  as  yet  be 
determined. 

The  minerals  accompanying  the  products  of  decomposition  in 
such  deposits,  particularly  of  calamine,  are  naturally  often 
limonite  and  other  ores  of  iron.  In  many  countries  these  play 
an  independent  part,  being  often  formed  by  the  metasomasis  of 
limestone,  as  proved  by  the  irregular  masses  of  the  deposits 
and  the  contained  fossils  transformed  into  ore. 

Alsace. — An  instance  is  furnished  by  the  so-called  Bohneisen- 
erze  of  Alsace  and  adjacent  regions  which  have  been  described 
and  correctly  explained  by  Daubree.* 

At  Liebfrauenberg,  irregular,  lean  beds  of  this  character, 
composed  principally  of  limonite,  but  scarcely  workable  with 
profit,  lie  on  both  sides  of  an  anticlinal  of  Yosges  sandstone, 
and  are  covered  with  alluvium.  In  one  place,  however,  near 
Goersdorf,  an  undecomposed  body  of  pyrite  and  mispickel 
occurs  instead  of  limonite. 

Cumberland. — In  Cumberland,  limonite-deposits  occur  on  the 
contacts  of  the  Carboniferous  Mountain  limestone,  both  with 
the  overlying  millstone  grit  and  with  the  underlying  Silurian 
schists.  They  are  connected  with  fault-fissures,  on  both  sides 
of  which  they  appear  as  is  shown  in  Fig.  89,  taken  from  a  paper 
by  Mr.  J.  D.  Kendall,  f 

Carniola. — The  Alps  offer  some  remarkable  examples  of  Boh- 
neisenerze.  These  occur,  according  to  A.  von  Morlot,J  in  the 

*  Les  Eaux  Souterraines  aux  Epoques  Anciennes,  p.  79. 
f  Trans.  N.  of  E.  Inst.  of  M.  E.,  1878,  vol.  xxviii.,  pi.  xxviii. 
J  "Geol.  Verhaltn.  von  Ober-Krain,"  Jahrb.  d.  k.  k.  Oeol.  E.  A.,  i.,  1850,  p. 
407. 


THE    GENESIS    OF    ORE-DEPOSITS.  137 

region  of  Wochein  in  Carniola  (known  for  its  iron-ores  and 
bauxite)  in  the  dolomite  and  limestone  mountains  only,  and 
either  in  the  form  of  beds  under  the  dolomite  detritus,  or  in 
clay,  in  the  caverns  of  the  dolomite.  Fig.  90  is  a  section  show- 
ing the  latter  form.  In  this  case  the  flatter-lying  cavern  was 
partly  filled  with  lime-detritus  and  clay  up  to  its  connection 
with  a  higher  vertical  cavern,  while  the  latter  was  filled  with 
Bohnerze  enclosed  in  loam,  and  had  been  mined,  according  to 
Morlot,  to  the  considerable  depth  of  250  meters  (820  feet). 
Here  and  there  a  nucleus  of  pyrite  is  found  in  the  iron-ore. 
The  beds  and  mass-deposits  of  bauxite  associated  with  limonite 
sometimes  show  also  the  "  bean-structure." 

c.  Deposits  in  Crystalline  Schists  and  Eruptive  Rocks. 

Without  entering  here  upon  a  discussion  of  the  subject  of 
regional  metamorphosis,  I  may  remark  that,  as  a  general  rule, 
the  older  a  rock  is,  the  more  changes  it  will  be  found  to  have 
undergone ;  yet  that  these  changes  do  not  advance  in  all  places 
uniformly.  Many  Cretaceous  and  Tertiary  formations  of  the 
Alps  present  a  highly  metamorphosed,  and  therefore  ancient, 
appearance ;  while  many  Silurian  formations — as,  for  instance, 
that  which  surrounds  St.  Petersburg — have  been  so  little  altered 
that  the  fossil  shells  which  they  contain  still  have  the  mother- 
of-pearl  luster.  Some  regions,  in  a  word,  have  been  more 
strongly  attacked  than  others,  through  causes  which  we  will  not 
here  pause  to  consider ;  and  when  we  follow  the  stratified  groups 
downward,  we  come  upon  the  various  crystalline  schists,  often 
traversed  by  eruptives,  and  showing  no  longer  any  trace  of  the 
clastic  sediments,  which  have  been  wholly  transformed  to  crys- 
talline masses.  We  cannot  hope  to  find  petrified  organisms  in 
these  masses ;  but  the  occurrence  of  disorganized  organic  ma- 
terial in  the  form  of  anthracite  and  graphite  proves  that  at  the 
time  the  rocks  were  formed,  organic  life  must  have  been  repre- 
sented in  the  sediments. 

Many  indications,  available  in  the  distinctly  sedimentary  rocks 
as  guides  in  the  determination  of  the  relative  age  of  their  ore- 
deposits,  are  here  wanting.  The  bedding  becomes  more  and 
more  obscure,  and  is  sometimes  no  longer  distinguishable  from 
the  cleavage.  Many  of  the  ore-deposits  in  these  rocks  have 
also  become  in  whole  or  in  part  crystalline,  adjusting  themselves 


138  THE    GENESIS    OF    ORE-DEPOSITS. 

to  the  prevailing  stratification  or  cleavage,  so  that  most  of  them 
present  a  bed-like  structure  and  form.  Whoever  believes  in 
the  possibility  of  a  contemporaneous  formation  of  the  ores  with 
the  rocks  will  not  trouble  himself  here  with  genetic  speculation, 
but  will  see  in  these  deposits  simply  "  ore-beds,"  according  to 
the  old  classification. 

Taberg^  Sweden. — The  circumstance  that  magnetite  is  a  con- 
stituent of  many  eruptive  rocks  has  inclined  many  geologists 
to  regard  masses  of  magnetite  in  the  neighborhood  of  such  rocks 
as  immediately  belonging  to  them.  This  theory  originated  in 
connection  with  the  Taberg  deposit,  in  Sm  aland,  Sweden,  and 
was  propagated  by  F.  L.  Haussmann,*  W.  Hissinger,f  and  A. 
Daubree;{  and  Taberg  has  been  regarded  ever  since  as  an  ex- 
ample of  the  primitive  existence  of  magnetite-deposits,  those 
of  Kackanar,  Yisokaya,  G-ora,  and  Blagodat  being  classed  with 
it. 

The  question  arises,  where  the  line  is  to  be  drawn  between 
an  eruptive  rock  containing  magnetite  and  a  magnetite  deposit. 
An  eruptive  rock,  like  that  of  Samokov,  in  the  Pils  moun- 
tains in  Bulgaria,  from  the  weathered  detritus  of  which  mag- 
netite is  obtained  by  ore-dressing,  is  not  properly  an  ore-deposit ; 
but,  on  the  other  hand,  that  of  Taberg,  where  the  ore  is  not 
only  finely  disseminated  in  large  amount,  but  also  occurs  in 
separate,  solid  veins,  may  fairly  be  so  called.  According  to  A. 
Sjogren,§  the  rock  consists  of  olivine,  magnetite,  and  a  little 
plagioclase,  with  mica  and  apatite  as  accessories.  In  other 
words,  it  is  an  already  metamorphosed  rock.  Considering  that 
at  several  places  in  Scandinavia  magnetite  occurs  in  the  crystal- 
line schists  also,  it  seems  unlikely  that  the  magnetite  of  Taberg 
belongs  to  the  primitive  rock.  This  is  confirmed  by  the  obser- 
vation of  Th.  Kjerulf,  that  all  the  ore-deposits  of  Norway  follow 
the  courses  of  eruptive  rocks.  Taberg  will  scarcely  prove  to  be 
an  exception,  and  may,  therefore,  be  regarded  as  a  secondary 
or  xenogenous  ore-deposit. 

Before  proceeding  further  I  must  mention  the  action  of  the 

*  Reise  durch  Skandinavien,  Gottingen,  1811-18,  i.,  p.  165. 

f  Versuch  einer  mineralog.  Geographic  von  Schweden  (Woehler's  translation),  1826, 
p.  205. 

J  Scandinaviens  Erzlagerstatten  (edited  by  G.  'Leonhard),  Stuttgart,  1846,  p.  25. 
\  Neues  Jahrb.f.  Mineralogie,  1876,  p.  434. 


THE    GENESIS    OF    ORE-DEPOSITS.  139 

mineral  solutions  upon  the  country-rock  of  some  veins,  which 
might  be  also  classed  as  impregnation.  In  this  respect  tin- 
deposits  are  most  interesting,  because  they  carry  ore,  not  only  in 
the  space  of  discission,  Le.,  the  vein-fissure,  but  to  a  large  extent 
in  the  neighboring  country-rock  also.  If  the  veins  occur  in 
granite,  this  is  changed  for  a  certain  width  into  greisen,  i.e.,  it  is 
robbed  of  its  feldspar,  which  is  even,  in  some  cases,  replaced 
by  cassiterite  and  associated  minerals.  Thus  are  formed  the 
beautiful  pseudomorphs  of  cassiterite  after  feldspar,  which 
adorn  many  mineral  collections.  (See  Fig.  91.) 

Figs.  91-93  are  taken  from  C.  Le  Neve  Foster.*  Fig.  91 
represents  the  alteration  of  the  granitic  country-rock  to  greisen 
on  both  sides  of  a  fissure,  which  is  here  filled  with  symmetrical 
quartz-crusts,  to  the  central  druse  or  comb.  Often  such  fissures 
occur  close  together ;  and  since  each  has  its  own  zone  of  grei- 
sen, the  result  is  a  Stockwerk,  constituting  a  metamorphosis  of 
the  granite,  and  formed  by  these  fissures. 

Cornwall. — In  the  slate  or  killas  of  the  Cornish  miners,  there 
is  often  a  disturbance  of  the  bedding  in  the  neighborhood  of  the 
fissure  (Fig.  92),  such  as  is  observed  in  connection  with  fault- 
fissures  elsewhere;  but  in  this  case  the  capel,  or  adjacent  portion 
of  the  slate,  is  altered  chemically  also,  being  impregnated  with 
quartz  and  traversed  by  streaks  of  ore.  The  fissure  itself  is 
filled  with  quartz,  cassiterite,  chlorite,  pyrite,  and  fragments  of 
the  capel.  When  several  fissures  come  together,  the  result  is 
somewhat  complicated,  but  can  be  reduced  to  the  simple  case 
just  described. 

Still  more  interesting  is  the  tin-deposit  of  East  Wheal  Lovell, 
described  by  the  same  authority. f  At  the  side  of  a  narrow 
quartz  vein  the  ores  occur  in  the  granite,  from  which  they  are 
not  separated  by  any  definite  boundary,  so  that  the  ore-body  is 
an  almost  vertical  shoot,  confined  to  the  neighborhood  of  the 
fissure,  yet  lying  in  the  country-rock.  It  is  clear  that  a  mineral 
water  of  high  solvent  power  must  have  ascended  under  great 
pressure,  in  order  to  bring  about  such  effects  in  a  rock  ordi- 
narily regarded  as  insoluble.  Fig.  93  shows  the  situation  of 

*  "Remarks  on  some  Tin-Lodes  in  the  St.  Agnes  District,"  Trans.  Roy.  Geol. 
Soc.  of  Cornwall,  1877,  ix.,  pi.  iii. 

f  C.  Le  Neve  Foster,  "Remarks  upon  the  Tin-Deposits  of  East  Wheal  Lovell," 
Trans.  Roy.  Geol.  Soc.  of  Cornwall,  1876,  Ix.,  pi.  ii. 


140  THE    GENESIS    OF    ORE-DEPOSITS. 

one  of  these  ore-shoots  in  granite,  at  the  East  Wheal  Lovell 
mine. 

The  ore-deposits  in  metamorphous  and  eruptive  rocks  occur 
especially  in  the  great  crystalline  northern  areas,  in  Scandi- 
navia, Canada,  and  the  northeastern  United  States. 

Scandinavia. — In  Scandinavia,  the  science  of  ore-deposits,  like 
that  of  petrography,  has  had  a  comparatively  independent  de- 
velopment. Although  these  countries  have  been  often  visited 
by  foreign  observers,  few  analogies  with  European  deposits 
have  been  noted — chiefly,  no  doubt,  because  of  the  peculiar 
character  of  the  occurrences  examined,  but  also  partly  because 
of  the  differing  standpoints  and  views  of  native  observers.  In 
recent  times  a  difference  of  interpretation  has  developed  itself 
between  the  Norwegian  and  the  Swedish  geologists ;  and  the 
former,  since  Kjerulf,  have  approached  more  nearly  the  Conti- 
nental view. 

As  already  remarked,  Kjerulf  traces  all  the  ore-deposits  of 
Norway  to  the  filling  of  spaces  of  discission,  and  particularly  of 
a  peculiar  space,  produced  by  the  sliding  of  the  rock  along  a 
bedding-plane,  and  locally  called  a  Lineal. 

With  respect  to  the  ore-filling,  he  points  out  that  the  occur- 
rence of  the  ore-deposits  must  always  be  studied  on  the  large 
scale,  and  that  this  method  shows  the  ore-deposits  to  occupy 
certain  lines,  characterized  by  the  presence  of  eruptive  rocks.* 
The  ores  appear  chiefly  in  the  crystalline  schists,  but  also  in 
traces  along  the  contact,  and  sometimes  in  the  eruptive  rocks 
themselves.  In  the  first  case,  the  different  sulphides,  mostly 
accompanied  with  quartz,  lie  parallel  with  the  bedding  or 
cleavage  of  the  rock,  and  thus  look  like  beds ;  but  their  second- 
ary origin  is  indicated  by  the  slickensides,  the  branching  of 
the  deposits  and  other  signs.  Sometimes  it  is  made  evident 
by  the  course  of  the  ore-masses,  cutting  across  the  bedding  or 
cleavage.  In  the  museum  at  Christiania  there  are  many  large 
specimens  of  the  ore,  some  of  which,  having  been  polished, 
show  this  structure  plainly.  Pictures  of  some  of  them  have 
also  been  published  by  Kjerulf.  f 

*  Die  Geologic  des  siidl.  u.  mittl.  Norwegen  (authorized  German  edition,  by  Dr.  A. 
Gurlt),  Bonn,  1880,  pp.  81,  284,  293. 

t  "  Pragstufer  med  Braeciestruktur  fra  Muggruben  og  Stovarts,"  Magazinfor 
Naturvidens,  Xobern,  xxvii.,  B.,  p.  335. 


THE    GENESIS    OF    ORE-DEPOSITS.  141 

In  this  connection,  the  primitive  ore-bearing  character  of  the 
Fahlbander  (so  often  cited  by  geologists  as  primary  ore-beds, 
which  enrich  the  veins  by  which  they  are  crossed)  is  entirely 
denied  (1.  c.,  p.  323).  It  has  been  proved  that  the  ores  of  the 
Modum  fahlbands  are  connected  with  malakolite  and  the  au- 
gite  rock  which  intrudes  in  "  lineal  "  form  between  the  steep 
strata  of  quartz-schists.  Figs.  94  and  95  are  intended  to  show 
the  appearance  of  these  deposits,  formerly  deemed  to  be  beds. 
The  former  represents  a  specimen  from  the  Kongens  mine  at 
Roras,  and  the  latter  a  part  of  the  specimen  illustrated  by 
Kjerulf,  from  the  Mug  mine  atTrondhjem.  In  the  former,  the 
subsequent  entrance  of  the  ore  is  at  once  recognized.  The 
latter  appears  as  if  the  crystallization  of  the  minerals  had  taken 
place  after  the  ore-impregnation. 

Of  course,  the  political  boundary  does  not  divide  the  nature 
of  the  ore-deposits  of  the  Scandinavian  kingdoms.  Those  of 
Sweden  are  often  the  continuations  of  the  Norwegian.  The 
crystalline  rocks  are  here  peculiarly  developed,  and  have  also 
been  peculiarly  named  by  the  Swedish  petrographers.  In  the 
Swedish  granulite,  for  instance,  one  would  scarcely  recognize 
its  Continental  namesake.  These  rocks  are  not  in  general  so 
coarsely  crystalline  that  their  constituent  minerals  can  be  dis- 
tinguished with  the  naked  eye.  The  so-called  eurites  are  still 
finely  crystalline,  and  the  halleflinta  is  almost  amorphous,  con- 
sisting only  of  the  ground-mass  of  the  massive  rocks.  The  beds 
and  mass-deposits  of  the  crystalline  rocks  ar,e  often,  like  many 
of  the  Norwegian  deposits,  associated  with  talcose  and  chloritic 
slates.  Sometimes  limestone  is  also  present,  as  at  Falun,  Tuna- 
berg,  etc.,  where  the  ores  lie  on  the  limestone  contacts.  The 
ores  of  some  of  the  deposits  suffer  in  depth  a  remarkable  change. 
Thus  the  mass  of  copper  pyrites  at  Falun  has  diminished  in 
depth ;  but  on  the  other  hand,  gold-bearing  quartz-veins  appear 
in  the  midst  of  the  pyritic  body,  and  have  yielded  in  recent 
years  considerable  amounts  of  gold. 

Ammeberg. — I  will  cite  as  an  example  one  of  the  most  inter- 
esting deposits,  namely,  the  zinc-blende  mine  of  Ammeberg,* 
belonging  to  the  Yieille  Montagne  Company,  which  I  have  per- 
sonally examined. 

*  A.  Sjogren,  "  Undersokning  of  den  omgrifande  Bergarten  on  Ammebergs  Gruf- 
vor."     Geol.  Foreningens  i  Stockholm  Fb'rhandl,  1880,  v. 


142  THE    GENESIS    OF    ORE-DEPOSITS. 

In  a  winding  line,  chiefly  E.-W.,  and  about  3J  kilom.  (2  m.) 
in  length,  occur  steeply-dipping  beds  of  zinc-blende  in  granu- 
lite,  or  gneiss  resembling  granulite.  At  certain  points  they 
show  very  beautiful,  close  folds.  At  first  glance  they  seem  to 
be  genuine  intercalated  beds  of  the  same  age  as  the  rock.  The 
ores,  however,  do  not  continue  along  the  whole  line,  but  form 
separate  lenses,  up  to  15  meters  (49  feet)  thick,  which  show  a 
distinct  stratification,  consisting  in  layers  of  fine-grained  to 
amorphous  material  resembling  halleftmta,  alternating  with  the 
coarser  granulite.  Fig.  96  is  a  polished  specimen,  which  ex- 
hibits clearly  the  secondary  ore-invasion.  The  original  bedding 
is  here  indicated  by  a  series  of  light  and  dark  dense  halleflinta 
layers ;  and  these  are  broken  through  by  masses  of  coarsely 
crystalline  rock  and  of  ore.  The  entrance  of  the  ore  into  the 
coarsely  crystalline  layers  seems  to  have  been  attended  by  an 
enlargement  of  their  volume,  which  resulted  in  their  breaking 
through  the  dense  layers. 

The  same  explanation  is  required  for  some  parts  of  the  bed, 
in  which,  between  the  plane  surfaces  of  two  fine-grained  barren 
strata,  ore  occurs  in  highly  folded  and  contorted  layers.  This 
folding  is  due  by  no  means  to  an  exterior  mechanical  energy, 
but  to  interior  chemical  forces. 

Some  of  the  blende  layers  carry  a  considerable  admixture  of 
galena,  as,  for  instance,  the  two  ore-layers  shown  in  Fig.  97, 
separated  by  a  fine-grained,  yellow  to  brown,  barren  stratum  of 
eurite.  The  whole  mass  is  traversed  by  fine  fissures  perpen- 
dicular to  the  bedding,  which  are  filled  with  leaf-silver,  looking 
like  tin-foil.  A  replacement  with  ore  of  the  original  rock-con- 
stituents is  here  beyond  question. 

It  is  supposed  that  the  blende  has  taken  the  place  of  the  mica 
of  the  granulite.  But  the  whole  country-rock  also  is  metamor- 
phous.  At  the  open  cut  of  the  G-odegard  II.  mine-working  I 
found  in  the  midst  of  the  schists  what  I  took  to  be  limestone, 
but  I  subsequently  lost  on  my  journey  the  specimens  intended 
for  more  careful  examination.  But  petrographers  have  prob- 
ably long  since  determined  this  point. 

This  Ammeberg  deposit,  then,  although  so  distinctly  bedded, 
is  by  no  means  of  primitive  origin ;  and  still  less  can  such  an 
origin  be  supposed  for  the  others,  which  occur  as  lenses  of  the 
greatest  variety  of  filling,  enclosed  in  the  crystalline  schists. 


THE    GENESIS    OF    ORE-DEPOSITS.  143 

If  mica  may  be  replaced  with  zinc-blende,  magnetite,  etc.,  such 
a  change  will,  of  course,  be  confined  to  certain  portions  of  the 
rock,  immediately  within  range  of  its  cause ;  and  these  portions, 
as  distinguished  from  the  rest  of  the  country-rock,  are  to  be 
considered  mineral  deposits. 

Some  of  the  ore-deposits  of  the  Alps  have  a  certain  simi- 
larity to  those  of  Scandinavia;  for  instance,  Prettau,  in  the 
Ahrn  valley,  in  Tyrol;  Brennthal,  near  Miihlbach,  in  Salzburg; 
and  Schneeberg,  near  Sterzing,  in  Tyrol. 

Prettau  in  Tyrol. — There  is  here  a  very  ancient  copper-mining 
industry,  which  was  overwhelmed  in  1878  by  a  great  disaster, 
and  will  not  soon  recover ;  namely,  the  settlement  at  the  smelt- 
ing-works  was  buried  by  an  avalanche  so  deep  in  debris  that  it 
has  been  necessary  to  sink  shafts  nearly  20  meters  (65  feet)  deep 
and  mine  out  the  stock  of  manufactured  copper  and  other  ob- 
jects of  value. 

The  crystalline  schists,  which  here  strike  E.  and  W.,  and  dip 
steeply  S.,  contain  impregnations  of  copper  and  iron  pyrites, 
very  short  horizontally,  but  considerably  prolonged  on  the  dip. 
The  deposit  has  been  opened  to  a  vertical  depth  of  500  meters 
(1640  feet),  representing  600  meters  (1968  feet),  so  that  the 
horizontal  projection,  or  distance  between  the  top  and  bottom, 
is  only  350  meters  (1148  feet).  Figs.  56  and  57  are  a  vertical 
section  and  plan.  Figs.  54  and  55  are  sketches  from  the  roof 
and  side  of  the  Ottilie  gallery,  where  the  chlorite-slate  and 
pyrites  present  highly  complicated  forms,  somewhat  like  the 
structure  I  have  observed  in  the  Transylvania  rock-salt.  It  may 
be  explained,  in  my  opinion,  either  by  an  interior  increase  of 
volume  or  by  a  distortion  of  the  chlorite-slate  in  the  steep  west- 
ward-pitching line  indicated  by  the  ore-deposit.  It  is  extremely 
difficult  to  form  a  correct  conception  of  this  deposit.  I  was 
able  to  study  some  of  the  lower  levels  only. 

It  is  remarkable  that  the  pyrites-mine  of  Brennthal,  near 
Miihlbach,  shows  an  entirely  similar  structure  and  form  of  ore- 
bodies,  and  almost  the  same  westward  pitch  upon  the  E.- "W. 
plane  of  the  stratification.  It  looks  as  if  dynamic  movements 
connected  with  the  mountain  had  played  a  leading  part  in  thus 
determining  the  same  pitch  for  the  ore-bodies  of  deposits  on 
opposite  sides  of  the  Central  Alps. 

Where  the  ore-body  begins  to  grow  poor,  and  the  pyrites  ap- 


144  THE    GENESIS    OF    ORE-DEPOSITS. 

pear  disseminated  in  grains  and  crystals  through  the  chlorite, 
the  secondary  character  of  the  impregnation  is  clearly  recog- 
nizable. The  space  for  the  massive  ore-body  was  probably  pre- 
pared by  mechanical  forces.  That  a  metamorphosis  was  the 
cause  is  not  likely,  because  the  original  minerals  of  the  strati- 
fied group  could  scarcely  have  assumed  such  abnormal  form 
and  dimensions. 

The  older  rocks  occupy  in  America  large  areas ;  and  there 
also  many  ore-deposits  occur  and  are  worked  which,  although 
somewhat  unlike  those  of  Scandinavia,  belong  to  a  similar 
type.  I  do  not  intend  to  describe  here  the  numerous  and  well- 
known  ore-deposits  of  the  Eastern  and  Northern  States ;  but  I 
cannot  avoid  brief  mention  of  some  peculiar  types. 

Lake  Superior. — The  copper-district  of  Lake  Superior  offers 
a  number  of  very  interesting  occurrences,  some  of  which, 
though  developed  by  extensive  mining,  and  often  described  at 
considerable  length,  have  not  yet  been  satisfactorily  explained. 
It  is  remarkable  that  copper  and  silver  occur  here  almost  ex- 
clusively native ;  but  it  is  very  generally  admitted  that  this  is 
not  the  usual  primitive  form  of  copper.  Sulphides  seem  to 
occur  but  seldom,  and  they  receive,  as  a  rule,  no  attention.  I 
saw  once,  at  Lac-la-Belle,  an  old  working  upon  pyrite,  chal- 
cosite  and  galena,  which  was  said  to  have  carried  some  native 
copper  in  its  upper  levels.  But  Foster  and  Whitney  do  not 
mention  it.* 

The  native  copper  of  this  district  occurs  notoriously  in  both 
veins  and  beds,  in  a  stratified  group  lying  between  the  Hu- 
ronian  and  the  Cambrian,  and  traversed  by  numerous  flows  of 
eruptive  rocks. f  We  are  here  concerned  with  the  beds.  The 
ore  in  the  Calumet  and  Hecla  mine  is  a  conglomerate  of  por- 
phyry pebbles;  another,  in  the  Copper  Falls  mine,  is  a  dark 
lava-flow,  the  so-called  "  ash-bed."  The  latter  is  impregnated 
with  copper  on  both  sides  of  the  Owl  Creek  vein,  which  trav- 

*  Report  on  the  Geology  and  Topography  of  a  Portion  of  the  Lake  Superior  Sand- 
District,  i.,  Washington,  1850,  p.  139. 

f  M.  E.  Wadsworth,  "Notes  on  the  Geology  of  the  Inland  Copper-Dist.  of  L. 
Superior,"  Bull,  of  Mus.  of  Comp.  Zool.,  Harvard  College,  Cambridge,  vii.,  1880. 

R.  Pilmpelly,  "  The  Paragenesis  and  Derivation  of  Copper  and  its  Associates 
on  Lake  Superior,"  Am.  Jour.  Sci.,  1872,  iii. 

K.  Duer  Irving,  "The  Copper-Bearing  Eock  of  L.  Superior,"  U.  S.  Geol.  Sur., 
3d  Ann.  Rep.,  Washington,  1883. 


THE    GENESIS    OF    ORE-DEPOSITS.  145 

erses  it  (Fig.  98) ;  while  in  the  Calumet  and  Hecla  conglomer- 
ate copper  sometimes  constitutes  the  cementing  material. 

In  both  masses  the  spaces  now  filled  with  copper  were  un- 
questionably once  filled  with  other  substances ;  and  the  present 
conditions  are  the  result  of  whole  series  of  complicated  re- 
placements. 

R.  Pumpelly,  who  originally  believed  in  a  contemporaneous 
origin  of  the  copper  and  the  enclosing  rock,  became  subse- 
quently convinced  that  the  copper  had  replaced  especially  epi- 
dote  and  chlorite,  and  that  certain  phases  of  metasomatic  pro- 
cesses were  here  represented.  The  eruptive  rocks  have  usually 
been  strongly  attacked — for  instance,  the  pebbles  of  the  con- 
glomerate, the  rocks  on  Isle  Royale,  etc.  Some  portions,  on  the 
other  hand,  e.g.,  the  Ash-bed,  have  been  little  attacked.  The 
former  instance  (which  the  latter,  it  is  true,  contradicts)  was 
used,  long  before  Sandberger,  as  proof  of  a  sort  of  lateral- 
secretion  theory ;  and  now  and  then,  where  the  copper-bearing 
rock  was  overlain  by  an  eruptive  flow,  the  theory  of  descend- 
ing solutions  was  also  brought  into  play. 

Some  of  the  attempted  explanations  assume,  in  my  opinion 
correctly,  as  the  cause  of  the  first  ore-depositions,  the  action  of 
hot  springs — in  which  connection  it  is  only  to  be  emphasized 
that  these  thermal  effects  occurred  long  after  the  intrusion  of 
the  eruptive  flows  between  the  sedimentary  strata,  so  that  the 
ores  were  brought,  not  by  or  in  the  eruptives  themselves,  but  by 
the  later  springs,  from  great  depths  and  perhaps  from  consid- 
erable distances.  This  explanation,  applicable  to  all  the  de- 
posits, suits  also  the  exceptional  case  cited  by  E.  D.  Irving, 
namely,  the  Nonesuch  copper-bed  in  the  sandstone  of  Porcupine 
Mountain,  far  from  an  eruptive  outflow. 

As  to  the  condition  in  which  the  ores  were  first  deposited, 
and  the  manner  in  which  they  became  reduced  and  associated 
with  zeolites,  additional  data  must  be  sought  for  the  formation 
of  an  opinion. 

Sudbury,  Canada. — Quite  recently,  A.  B.  von  Foullon  has 
published  his  observations  in  the  Sudbury  region,  Canada,* 
expressing  certain  theoretical  conclusions  of  great  interest, 

*  "Ueber  einige  Nickelerzvorkommen,"  Jahrb.  d.  k.  k.  E.  A.,  xliii.,  1892,  p. 

276. 


146  THE    GENESIS    OF    ORE-DEPOSITS. 

which,  however,  flatly  contradicted  my  view.  They  concern 
the  pyritic  deposits  which  occur  in  Huronian  rocks,  but  at  the 
borders  of  eruptive  outflows  of  diorite,  etc.,  and  were  described 
by  T.  Gr.  Bonney*  and  afterward  by  R.  Bell.f  The  ores  are 
associated  with  masses  of  diorite,  intercalated  conformably  in 
the  stratified  rocks.  The  ore-bodies  have  the  form  of  "  stock- 
works,"  and  consist  of  an  irregular  mixture  of  rock  and  metal- 
lic sulphides  (?).  In  the  ore,  which  contains  gold,  platinum, 
tin,  lead,  silver,  zinc  and  iron,  occur  also  feldspar,  quartz  and 
apatite.  This  account,  taken  from  Bell's  description,  indicates 
a  strong  analogy  with  the  Scandinavian  deposits. 

Foullon,  who  made  in  this  field  a  series  of  highly  valuable 
observations,  supported  by  careful  chemical  analyses,  expresses 
himself  finally,  concerning  the  genesis  of  these  deposits,  as 
follows : 

' '  The  irregular  mixture  of  pyrites  and  silicates,  presenting  copper  pyrites  and 
magnetic  pyrites  enclosed  in  the  rock  in  the  most  varied  quantities  and  in  all  con- 
ceivable forms  ;  and,  furthermore,  the  circumstance  that  sometimes  the  ore  occurs 
disseminated  in  the  diorite,  and  sometimes  the  diorite  is  enclosed  in  the  ore,  now 
the  rock,  and  again  the  pyrites,  being  the  ground-mass,  prove  unmistakably  their 
contemporaneous  origin.  At  certain  periods  of  the  diorite  eruption,  the  magma 
was  rich  in  accessory  constituents  which  rendered  possible  the  formation  of  the 
metallic  sulphides  ;  and  these  were  segregated  during  solidification." 

R.  Bell  has  expressed  himself  still  more  plainly. 

"  The  ores  are  not  of  humid,  but  of  molten  origin,  as  is  proved  by  their  occur- 
rence in  the  diorite,  with  which  they  ascended.  The  masses  of  molten  diorite  must 
have  remained  long  liquid,  so  that  the  metallic  sulphides  could  separate,  become 
concentrated  at  certain  points,  and  continue  with  the  fragments  of  diorite.  Large 
quantities  of  the  molten  diorite,  and  the  heavy  metals,  must  have  retired  again." 

These  surprising  statements  assume  a  chemical  impossibility, 
namely,  the  presence  of  metallic  sulphides  in  the  magma  of  the 
molten  eruptive  rock,  after  the  fashion  conceived  by  H.  C.  von 
Leonhard,J  on  the  strength  of  metallurgical  analogies. 

Shaft-furnaces,  operated  for  a  separation  of  the  ingredients 
of  the  charge,  produce  slag,  metallic  sulphides  (matte)  and 

*  "  Notes  on  a  Part  of  the  Huronian  Series  in  the  Neighborhood  of  Sudbury," 
Quart.  Jour.,  B.,  xliv.,  1888. 

t  "The  Nickel-  and  Copper-Deposits  of  Sudbury  District,"  Bull.  Geol.  Soc.  of 
Am.,  ii.,  Eochester,  1891. 

J  Hilttenerzeugnisse  und  andere  auf  kunstlichem  Wege  gebildete  Minercdien  cds  Stiitz- 
punkte  geologischer  Hypothesen,  Stuttgart,  1858. 


THE    GENESIS    OF    ORE-DEPOSITS.  147 

reguline  metal.  But  the  above  hypothesis  involves  rather  a 
common  fusion  of  all,  and  a  separation  in  cooling  of  slag  (diorite) 
and  matte  (metallic  sulphides).  These  authors  should  certainly 
not  omit  to  explain  further  the  principles  upon  which  their  ex- 
planation is  based,  taking  into  consideration  at  the  same  time 
the  inner  structure  and  other  relations  of  the  deposits  in  ques- 
tion, such  as  their  conformity  with  the  stratified  rocks  of  the 
region ;  the  occurrence  of  ore-channels,  quite  similar  to  those 
encountered  in  deposits  formed  by  aqueous  circulation,  etc. 

These  pyritic  deposits  contain  almost  all  the  heavy  metals, 
including  platinum  and  gold,  and  it  is  remarkable  that  the 
latter  here  occurs  in  quartz,  exactly  as  it  does  generally,  through- 
out the  world. 

The  untenable  character  of  the  explanations  above  quoted 
must  be  evident,  and  this  brief  mention  of  them  will  be  suffi- 
cient. Yet  it  appears  that  there  are  other  inquirers  into  the 
genesis  of  ore-deposits  who  purpose  to  take  a  similar  stand- 
point.* 

4.  HYSTEROMORPHOUS  DEPOSITS. 

Under  this  title  are  included  the  deposits  formed  by  the 
chemical  and  mechanical  influences  of  the  surface-region,  from 
the  original  deposits  of  which  the  conditions  of  origin  have 
been  considered  above.  These  formations  have  been  consid- 
ered and  named  from  various  standpoints.  Thus  the  name 
"  deposits  of  debris "  emphasizes  the  idea  of  a  mechanical 
crushing  or  disintegration ;  the  German  term  Seife,  like  the 
Spanish  and  American  "  placer,"  is  based  upon  the  manner  in 
which  such  deposits  are  often  mined  for  their  metallic  contents, 
and  so  on.  The  expression  "  secondary  deposits  "  satisfies,  it 
is  true,  the  definition  given  above,  but  is  rendered  ambiguous 
by  its  frequent  use  in  other  meanings  connected  with  the  genesis 
of  ores.  I  feel  warranted,  therefore,  in  proposing  for  this  group 
the  more  distinctly  significant  name  "  hysteromorphous  "  (later- 
formed). 

The  influences  of  the  present  surface  upon  deposits  found  in 
the  deep  region  are  so  characteristic  as  to  permit  us  to  draw 
conclusions  concerning  the  processes  of  earlier  periods,  when 

*  For  instance,  J.  H.  L.  Vogt,  of  Christiania,  "Bildungvon  Erzlagerstatten 
durch  Differentiationsprozesse  im  basischen  Eruptionsmagma." — Zeitsch.f.  prakt. 
GeoL,  1893,  i.,  p.  4. 

10 


148  THE    GENESIS    OF    ORE-DEPOSITS. 

the  surface  occupied  a  very  different  position.  Unquestionably, 
effects  similar  to  those  of  to-day  were  produced  then  also,  and 
we  must  include  in  our  consideration  of  the  subject  the  hystero- 
morphism  of  former  geological  periods. 

a.   Chemical  Effects. 

The  chemical  effects  proceeding  from  the  present  surface  have 
been  already  discussed  in  many  respects.  They  involve  not 
only  phenomena  on  the  surface  itself,  but  extend  beneath  it  to 
the  groundwater  level,  and  even  below  that  level,  so  far  as  the 
vadose  circulation  is  traceable. 

On  the  surface  it  is  especially  the  oxidizing  effect  of  the 
atmosphere,  its  contained  carbonic  acid,  and  the  solvent  and 
chloridizing  action  of  atmospheric  precipitation,  simultaneously 
aided  by  the  mechanical  effects  of  wind  and  moving  water, 
which  bring  about  what  Justus  Roth*  has  called  "  simple 
weathering,"  to  distinguish  it  from  more  complicated  forms  of 
decomposition.  In  considering  not  merely  rocks,  but  outcrops 
of  complex  ore-deposits,  we  encounter  what  Roth  calls  "  com- 
plicated weathering." 

Decomposition  underground,  through  the  action  of  the  same 
atmospheric  constituents  of  the  surface-water,  extends,  as  is 
well-known,  to  the  groundwater  level,  where  it  may  manifest 
itself  in  a  striking  way  by  reason  of  the  frequent  occurrence  at 
that  level  of  the  alternation  of  dryness  with  moisture,  which  is 
a  factor  greatly  promoting  decomposition. 

A  similar  condition  is  presented,  as  was  pointed  out  in  Part 
I.,  by  the  workings  of  mines,  where  the  water-level  has  been 
artificially  lowered,  and  a  zone  of  depth  previously  untouched 
by  the  vadose  circulation  is  brought  within  the  domain  of  that 
agency.  Deep  and  old  metal-mines  especially  exhibit  in  a 
striking  way  the  effects  of  the  vadose  circulation,  and,  in  addi- 
tion, a  phenomenon  but  seldom  found  in  places  under  the  in- 
fluence of  the  natural  water-level,  namely,  the  effect  of  the 
mine-waters  upon  various  surface  relations  and  products. 

Limonite-Deposit  near  Rio  Tinto,  Spain. — One  of  these  rare 
instances  is  cited  by  J.  A.  Phillipsf  in  his  group,  "  Deposits 

*  Allgem.  u.  Chem.  Geologic,  vol.  i.,  Berlin,  1879,  pp.  69-159. 
f  A  Treatise  on  Ore-Deposits,  London,  1884,  p.  15. 


THE    GENESIS    OF    ORE-DEPOSITS.  149 

resulting  from  chemical  action."  Namely,  in  the  vicinity  of 
the  great  iron  and  copper  pyrites-deposits  of  Rio  Tinto,  in 
Spain,  there  occurs  a  deposit  of  hydrate d  ferric  oxide,  shown 
by  the  fossils  it  contains  (which  correspond  with  species  still 
living  in  the  region)  to  be  of  recent  origin,  and  undoubtedly 
produced  by  the  weathering  and  decomposition  of  the  neigh- 
boring pyritic  deposit.  It  was  deposited  in  a  swamp-like  basin 
with  peaty  matter,  and  subsequent  erosion  has  left  of  it  two 
remnants  only,  at  Mesa  de  los  Pinos  and  Cerro  de  las  Yacas 
respectively.  Evidently,  in  this  case,  the  detritus  of  the  pyritic 
deposit  has  not  been  mechanically  swept  away  and  collected 
elsewhere,  but  a  chemical  action  has  taken  place,  removing 
material  in  solution,  exactly  as  in  the  formation  of  bog  iron- 
ores.  The  formation  here  is  certainly  earlier  than  the  Roman 
period,  for  Roman  tombstones  have  been  found,  made  of  this 
recent  iron-ore. 

Mine- waters  contain  the  solutions  of  all  substances  directly 
or  indirectly  dissolved  by  the  vadose  circulation,  and  some  of 
these,  encountering  suitable  precipitants,  may  be  thrown  down. 
Thus,  ferrous  oxide  becomes  by  oxidation  hydrated  ferric  ox- 
ide ;  many  metallic  sulphates  are  reduced  by  organic  matter  to 
sulphides ;  copper-salts  may  even  be  thus  reduced  to  metal, 
etc.  These  new  precipitates  will  mark  the  track  of  the  mine- 
waters. 

Finally,  while  the  solutions  formed  by  surface-waters,  like 
those  of  the  mine-waters,  mostly  find  their  way  to  the  points 
where  the  water-level  reaches  the  surface  (drainage-points),  yet 
as  a  part  of  the  groundwater  penetrates  to  greater  depths,  such 
solutions  may  very  likely  produce,  in  the  deep  region  itself, 
impregnations,  which  must,  however,  differ  in  character  from 
those  produced  by  the  deep  circulation  proper. 

The  primitive  deposit  from  which  such  solutions  have  come 
will  show  remaining  in  it  principally  substances  not  easily 
soluble,  together  with  such  as,  like  precious  stones,  resist  all 
atmospheric  influences.  Meteoric  waters,  carrying  oxygen, 
some  carbonic  acid,  and  small  quantities  of  chlorides,  will  first 
oxidize  whatever  is  oxidizable,  especially  the  metallic  sulphides. 
On  this  subject  S.  H.  Emmens*  has  published  a  clear  statement, 

*  "  The  Chemistry  of  Gossan,"  E.  and  M.  J.,  1892,  liv.,  p.  582. 


150  THE    GENESIS    OF    ORE-DEPOSITS. 

with  some  practical  deductions.  He  distinguishes  in  the  order 
of  liability  to  decomposition  the  following  degrees  :  (1)  mar- 
casite,  (2)  pyrite,  (3)  pyrrhotite,  (4)  chalcopyrite,  (5)  bornite, 
(6)  folgerite,  (7)  millerite,  (8)  chalcosite,  (9)  galena,  and  (10) 
zinc-blende.  The  acid  ferric  sulphate  formed  from  the  first 
members  of  this  series  immediately  attacks  the  latter  members. 
The  carbonic  acid  contained  in  the  circulating  waters  has  a 
high  solvent  power,  and,  among  other  things,  dissolves  the 
carbonate  of  lime  as  a  bicarbonate,  which  reacts  upon  the  basic 
sulphates,  producing  gypsum  and  free  carbonic  acid,  and  ulti- 
mately transforming  lead  sulphate  into  carbonate  (cerussite). 
Copper  oxide  and,  under  some  circumstances,  native  copper, 
may  be  formed  from  copper  sulphate,  and  so  on. 

For  the  chlorine  of  the  chlorides,  lead  and  silver  have  the 
strongest  affinity,  and  these  metals  will  consequently  be  often 
found  in  the  upper  zone  as  chlorides. 

The  decomposition  above  water-level  of  gold-  and  silver- 
bearing  deposits  facilitates  the  extraction  of  these  metals. 
Metallic  gold  can  be  extracted  by  simple  processes  of  me- 
chanical concentration  and  amalgamation  from  oxidized  ma- 
terial, while  gold  in  undecomposed  sulphides,  etc.,  must  be 
roasted,  smelted,  or  chlorinated  with  more  or  less  cost  and 
difficulty.  Silver  likewise  occurs,  as  a  rule,  in  this  upper  de- 
composed zone  in  the  form  of  easily  amalgamated  combinations 
(free-milling  ores),  while  the  refractory  ores  of  deeper  zones  are 
much  harder  to  treat. 

It  is  doubtless  for  these  reasons  that  mining  enterprises  often 
come  into  very  critical  conditions  when  they  reach  water-level, 
and  many  mines  even  cease  to  be  profitable.  An  important 
part,  no  doubt,  is  played  by  other  causes,  such  as  the  necessity 
of  hoisting  increased  quantities  of  water,  the  cost  of  the  required 
machinery,  etc. 

It  is  remarkable  that  in  western  North  America  the  ground- 
water  level  lies  deeper  than  is  generally  the  case  in  Europe. 
I  suppose  the  reason  to  be,  that  the  present  area  of  the  Interior 
Basin  of  North  America,  which  has  no  surface-drainage  to  the 
ocean,  was  formerly  cut  by  deep  valleys  of  erosion,  which  made 
a  deeper  escape  of  the  groundwater  possible.  This  suggestion 
is  confirmed  by  the  level  valleys  of  Utah  and  Nevada,  several 
miles  wide  and  filled  with  very  recent  sediments,  between  com- 


THE    GENESIS    OF    ORE-DEPOSITS.  151 

paratively  narrow  mountain  ranges,  which  seem  to  be,  so  to 
speak,  the  tops  only  of  the  former  ranges. 

In  Europe,  the  upper  zones  of  the  ore-deposits  were  worked 
out  long  ago,  at  a  time  when  the  science  of  chemistry  was  in 
its  infancy.  But  we  know  from  the  remnants  in  these  work- 
ings that  chlorides,  lead  and  silver  carbonates,  and  various  sul- 
phates, such  as  anglesite,  occurred  in  them,  though  they  were 
not  recognized.  In  Transylvania  the  decomposed  products  of 
the  outcrop-zone  were  called  Braunen,  ("  browns "),  with  evi- 
dent reference  to  the  brown  hydrated  ferric  oxide.  The  well- 
known  maxim  of  the  German  miners  concerning  the  "  iron 
hat  "  is  very  ancient ;  and  the  same  may  be  said  of  the  Cornish 
proverb,  "  Gossan  rides  a  high  horse."  Limonite  is  certainly 
a  characteristic  indication  of  the  outcrop  of  an  ore-deposit; 
and  no  doubt  its  reddish-brown  color  has  chiefly  suggested  the 
South  American  miners'  names,  pacos  and  colorados. 

In  a  few  instances  the  "  iron  hat "  has  been  actually  mined 
as  an  iron-ore.  As  a  rule  it  is  the  decomposed,  porous  and 
honeycombed  vein-material  of  the  upper  zone,  and  is  colored 
only  with  limonite.  The  part  of  the  ore-deposit  above  water- 
level  has  a  characteristic  appearance.  Quartz  and  other  refrac- 
tory gangue-minerals  are  surrounded  and  impregnated  by 
earthy  limonite  masses.  As  a  rule  the  original  texture  of  the 
deposit  has  become  obsure ;  and  sometimes  fragments  of  the 
mineral  crusts,  broken  off  and  crushed  through  changes  of 
volume,  are  found  chaotically  thrown  together.  Occasionally, 
however,  the  original  structure  may  still  be  traced  in  the  de- 
composition-products of  the  several  crusts,  unaltered  nuclei  of 
the  ore  being  discoverable  in  them.  Some  substances  (espe- 
cially calamine  formed  from  zinc-blende)  display  the  stalactitic 
forms  characteristic  of  the  vadose  region.  Original  druses  as 
well  as  recently  formed  cavities  are  filled  with  new  material ; 
and  in  this  way  a  secondary  crustification  may  occur. 

I  must  not  forget  to  mention  that  there  are  some  observations 
according  to  which  gold  has  been  precipitated  chemically  in 
hysteromorphous  deposits.  Oscar  Lieber,*  F.  A.  Genth  and 
A.  R.  C.  Selwyn  expressed  the  opinion  that  detrital  gold  gen- 
erally, or  a  portion  of  it,  has  been  deposited  from  solutions. 

*  In  Cotta's  Gangstudien,  and  in  Oeol.  Rep.  of  S.  Carolina,  1860. 


152  THE   GENESIS    OF    ORE-DEPOSITS. 

Laur,  J.  A.  Phillips,  Wilkinson,  dewberry,  Daintree,*  Skey, 
Egleston,f  etc.,  have  accepted  this  view  as  more  or  less  gener- 
ally applicable.  E.  CohenJ  has  undertaken  to  examine  it  critic- 
ally, and  is  inclined  by  his  own  experience  in  South  Africa  "  to 
adopt  the  conclusion  reached  by  Devereux  for  the  Black  Hills 
of  Dakota,  and  to  assume  that  by  far  the  largest  part  of  the 
detrital  gold  has  been  liberated  by  the  mechanical  destruction 
of  older  deposits  and  has  been  mechanically  laid  down  ;  while, 
on  the  other  hand,  a  precipitation  from  solutions  undoubtedly 
takes  place,  but  plays  a  very  subordinate  part  only." 

My  own  opinion  on  the  subject  is  expressed  in  the  above 
quotation.  §  !Nb  doubt  here  and  there,  in  the  detrital  deposits, 
traces  of  chemical  activity  are  discoverable ;  but  they  are  not 
sufficient  to  weaken  the  evident  proofs  of  the  mechanical  origin 
of  detrital  gold. 

b.  Mechanical  Effects. 

The  mechanical  effects  of  moving  air  and  water,  of  frost  and 
ice,  are  grouped  under  the  head  of  erosion,  and  are  treated  at 
length,  so  far  as  rocks  in  general  are  concerned,  in  the  geologi- 
cal text-books.  We  are  here  concerned  especially  with  effects 
of  this  kind  produced  upon  those  portions  of  ore-deposits 
which  are  exposed  at  the  surface.  We  notice  at  once  that  me- 
chanical, unlike  chemical  effects,  are  confined  to  the  surface  or 
a  very  small  distance  below  it.  In  general,  we  must  assume 
that  the  chemical  changes  took  place  first,  but  that  the  prog- 
ress of  erosion  brings  both  to  our  view  at  the  same  time. 

Verchoviky,  or  Surface-Deposits  in  Situ. — Not  only  water  and 
ice  (glaciers),  but  also  wind,  takes  part  in  erosion.  For  in- 
stance, if  an  ore-deposit,  by  reason  of  its  greater  resistance, 
crops  out  above  the  level  of  the  country,  the  wind  will  con- 
tinually tend  to  blow  away  the  finer  and  lighter  portions  of  the 
detrites  formed  by  chemical  processes  of  weathering ;  so  that, 
in  the  course  of  time,  there  must  remain  of  the  original  out- 
crop only  the  heavier  portions,  so  far  as  these  are  not  carried 

*  See  A.  G.  Lock's  Gold,  its  Occurrence  and  Extraction,  p.  746-800. 

f  "  The  Formation  of  Gold  Nuggets  and  Placer-Deposits,"  Trans.  A.I.  M.  E., 
ix.,  1881,  p.  633. 

J  "  Ueber  die  Entstehung  des  Seifengoldes,"  Mitth.  d.  Naturw.  Vereins  f.  Neu- 
pommern  u.  Riig&n,  xix. ,  1887. 

§  See  my  article,  "Zur  Genesis  der  Metallseifen,"  Oesterr.  Zeitsch.  /.  B.  u.  H. 
wesen,  1887,  xxxv.,  p.  325. 


THE    GENESIS    OF    ORE-DEPOSITS.  153 

away  by  water.  In  fact,  I  have  observed  in  the  Urals  that  the 
gold-diggings  of  the  valley,  undoubtedly  formed  by  water,  ex- 
tended up  the  slopes  to  points  where  this  could  not  have  been 
their  origin.  The  gold-bearing  weathering-detritus  is  then 
called  Nagornyje  rozsypy  and  Verchoviky. 

A  similar  feature  was  observed  by  "W.  C.  Kerr*  in  the  aurif- 
erous deposits  of  North  Carolina ;  and  I  have  seen  it  in  the  old 
gold-workings  of  Bergreichenstein  and  Nesvacil,  in  Bohemia,f 
where  flat  mountain  ridges  are  covered  with  old  pits  and 
dumps.  It  is  impossible  to  consider  them  as  diluvial  terraces, 
for  the  alluvium  passes  over,  so  to  say,  into  the  solid  gneissic 
rock,  which  is  traversed  by  many  quartz  veins.  The  gold 
occurs  concentrated  in  the  deepest  portion  of  the  weather-de- 
tritus, that  is  to  say,  on  the  contact  with  bed-rock,  and  has 
penetrated  all  the  open,  loosely-filled  fissures  in  the  latter. 

Cotta|  speaks  also  of  deposits  of  debris  in  place,  which  occur 
on  high  plateaus  and  mountain  slopes,  and  consist  of  products 
of  weathering  which  are  not  rounded  pebbles  or  sand  and 
slime,  accumulated  by  water-currents.  A.  Gr.  Lock§  speaks  of 
surface-deposits  being  "  a  result  of  the  disintegration  of  the 
rocks  in  situ,"  and  says : 

"The  gold  it  contains  is  quite  angular,  hackly,  or  crystalline,  and  is  derived 
from  auriferous  quartz  reefs  or  leaders,  existing  in  the  immediate  vicinity." 

Similar  conditions  obtain  very  significantly  in  the  Kackar 
district,  to  be  hereinafter  more  fully  described. 

Theory  of  the  Sinking  of  Heavier  Constituents. — But  the  great 
agent  in  the  transportation  and  re-deposition  of  the  metallic 
portions  of  original  deposits  has  unquestionably  been  flowing 
water ;  and  this  is  an  equal  factor  in  the  removal  of  the  rock- 
detritus  of  erosion,  which  it  is  constantly  striving  to  carry  to 
the  ocean.  River-sediments  are  notoriously  unstable.  What 
is  deposited  this  year  is  carried  further  down  stream  in  the 
years  next  following,  and  so  on  until  it  comes  to  comparative 

*  "Some  Peculiarities  in  the  Occurrence  of  Gold  in  North  Carolina,"  Trans. 
A.  I.  M.  £.,  x.,  475. 

t  "Zur  Genesis  der  Metallseifen,"  Oesterr.  Z.  f.  B.  u.  H.  wesen,  1887,  xxxv., 
p.  325. 

J  Erzlagerstatten,  i.,  Freiberg,  1859,  p.  100. 

§  Gold,  its  Occurrence,  etc.,  London,  1882,  p.  828. 


154  THE    GENESIS    OF    ORE-DEPOSITS. 

rest  in  the  sea.  The  original  deposits,  furnishing  the  material 
thus  transported  over  great  distances  and  areas  by  water,  are 
well  called  by  the  Russians  Korennyje  mestorozdenyje,  or  root- 
like  deposits, — that  is,  as  it  were,  the  roots  of  the  scattered  hys- 
teromorphous  deposits. 

The  attempt  has  been  made  to  explain  the  concentration,  es- 
pecially of  heavy  metals,  like  gold  and  platinum,  in  certain  pay- 
ing layers  of  the  detritus,  by  a  sort  of  natural  concentration 
process.  The  circumstance  that  the  richest  gold-deposits  most 
frequently  lie  in  the  lowest  stratum  of  the  detritus,  immediately 
on  the  bed-rock,  yet  that  several  such  horizons  occur  one  over 
the  other,  is  difficult  to  explain  in  this  way;  for  Cotta's  assumed 
separate  periods  of  formation  (op.  cit.,  i.,  p.  102)  are  scarcely 
satisfactory,  involving  as  they  do  either  periodic  transportation 
or  periodic  deposition,  neither  of  which  is  probable. 

I  believe  that  I  have  found  in  the  Ural  gold-placers  a  much 
more  probable  explanation,  based  on  the  principle  that  the  spe- 
cifically heavier  elements  of  a  loose  mass  are  able,  with  the  aid 
of  water,  to  work  their  way  down  through  the  lighter  portions. 
At  the  Przibram  concentrating-works  it  is  found  that  if  the 
pulp  is  left  standing  for  a  considerable  period,  the  galena  will 
accumulate  at  the  bottom.  In  gold-  and  platinum-concentrat- 
ing establishments  it  may  be  often  observed  that  these  heavy 
metals  find  their  way  into  the  floor  and  woodwork  of  the  mill, 
from  out  of  which  they  are  from  time  to  time  recovered  by 
working  up  these  materials.  Why  should  this  happen  in  arti- 
ficial operations  only,  and  not  also  under  natural  conditions, 
where  the  descent  of  the  heavier  portions  is  essentially  aided 
by  the  percolation  of  atmospheric  waters  through  the  loose  cov- 
ering-material ? 

This  view  is  supported  by  the  features  of  all  gold-placers, 
especially  those  of  the  detritus  of  weathering  in  place,  where 
the  agency  of  running  water  cannot  be  adduced,  and  the  accu- 
mulations of  gold  at  the  contact  of  the  loose  and  the  solid  ma- 
terial must  be  explained  by  its  sinking  through  the  former. 

Stream-Detritus. — The  detrital  deposits  produced  by  running 
water  are  generally  characterized  by  the  predominance  of  per- 
meable material,  such  as  sand,  gravel,  etc.  Under  this  cover- 
ing mass  lies  the  solid,  impermeable  "  bed-rock  "  or  "  rim-rock" 
of  the  Americans,  the  plotik  or  posva  of  the  Russians ;  and  in 


THE    GENESIS    OF    ORE-DEPOSITS.  155 

all  the  gold-fields  of  the  world  the  richest  pay-deposits  are 
found,  as  a  rule,  at  the  border  between  the  cover  and  the  bed- 
rock. If  the  latter  is  decomposed,  fissured,  or  otherwise 
loosened,  the  fine  gold  will  sink  into  it,  making  it  sometimes 
rich  enough  to  be  mined  and  concentrated ;  and  this  occurs 
without  regard  to  the  petrographic  character  of  the  rock.  Thus 
in  the  Ural,  palaeozoic  schists,  limestone  and  eruptive  rocks  in- 
differently are  charged  with  gold.  This  circumstance  indicates 
also  the  error  of  the  assumption  that  these  bed-rocks  originally 
carried  gold. 

But  layers  of  impermeable  material  sometimes  occur  in  the 
cover,  as,  for  instance,  lava-beds  in  Australia  and  California,  or, 
in  general,  solid  conglomerates  and  clays.  In  such  cases  there 
is  often  a  concentration  of  gold  on  the  more  solid  layer,  called 
in  America  the  "  false  bottom,"  and  in  the  Ural  loznyj  plotik — 
that  is,  a  material  erroneously  taken  for  the  bed-rock.  There 
are  often  in  the  detrital  cover  two  or  more  such  gold-bearing 
layers,  which  are  easily  explained  on  the  theory  above  sug- 
gested. The  hypothesis  of  a  natural  concentration  in  running 
water  is  embarrassed  by  the  fact  that  the  material  of  gold- 
placers  shows  no  arrangement  according  to  size,  but  consists, 
as  a  rule,  of  elements  of  all  sizes. 

The  movement  of  the  elements  of  a  loose  mass  has  been 
already  pointed  out  by  W.  C.  Kerr,*  who  admits  the  possibility, 
according  to  A.  G.  Lock,  of  the  sinking  of  the  heavier  parti- 
cles, though  this  is  only  in  a  passing  remark,  and  without  in- 
dication of  its  far-reaching  importance.  He  says  : 

"The  superior  weight  of  the  precious  atoms  would  cause  them  to  sink  through 
the  moist  surrounding  matters  till  a  hard  layer  was  met  with.  The  occurrence 
of  this  process  would  constantly  add  to  the  deposits,  the  gold  always  gravitating 
to  the  bottom,  quickly  or  slowly,  according  to  circumstances." 

It  seems  to  me  that  this  idea  must  have  impressed  itself  upon 
other  impartial  observers  also ;  and  I  can  only  wonder  that  it 
has  not  been  more  frequently  expressed. 

R.  Helmhacker  has  recently  communicated  some  observa- 
tions in  the  Altai  region  of  Siberia,  such  as  the  sinking  of 
heavy  metallic  objects  in  the  loose  wash,  which  confirm  the 

*  "The  Gold-Gravels  of  North  Carolina,"  Trans.  A.  I.  M.  R,  1880,  viii.,  p. 
462.  Gold,  its  Occurrence,  etc.,  London,  1882,  p.  916. 


156  THE    GENESIS    OF    ORE-DEPOSITS. 

above  views.  Among  other  things,  he  identified  grains  of  me- 
tallic lead  formed  in  the  gold-placers  as  shot,  scattered  in  hunt- 
ing, which  had  sunk  into  the  earth. 

As  is  well  known,  auriferous  detritus  occurs  not  only  in 
present  but  also  in  ancient  river-beds,  long  since  dry;  and 
since,  in  the  latter,  the  remains  of  diluvial  animals,  such  as  the 
mammoth,  etc.,  have  been  found,  a  distinction  has  been  made 
between  alluvial  and  diluvial  gold-deposits.  But  discoveries  of 
yet  older  organic  remains  have  shown  that  such  gold-deposits 
were  formed  in  still  more  ancient  periods.  The  old  river-beds 
of  California  cross  the  present  streams,  and  the  auriferous  de- 
tritus of  the  former  is  covered  with  thick  lava-beds — a  feature 
which  may  be  observed  in  Australia  also.  During  the  depo- 
sition of  the  gold,  therefore,  conditions  very  different  from 
those  of  the  present  day  must  have  obtained. 

In  another  respect,  also,  the  relation  between  ancient  and 
modern  river-beds  is  sometimes  peculiar.  The  late  channels 
have  been  rendered  by  erosion  deeper  than  the  older  ones. 
But  on  the  eastern  slope  of  the  Ural  this  is  almost  totally  re- 
versed. The  diluvial  gold-deposits  characterized  by  the  remains 
of  the  mammoth  often  lie  below  the  water-level  of  the  present 
streams,  so  that  the  latter  must  be  diverted  in  order  to  mine  the 
ancient  beds.  This  condition  apparently  extends  throughout 
the  whole  Siberian  plain,  and  may  be  taken  as  evidence  that 
the  erosive  energy  of  its  rivers  has  decreased  since  the  Diluvial 
period,  their  fall  having  been  reduced,  either  by  the  accumula- 
tion of  the  erosion-detritus  or  by  changes  in  the  relative  alti- 
tude of  the  Ural  range. 

The  eastern  slope  of  the  Ural  is  characterized  by  numerous 
lakes  and  swamps  along  the  tributary  streams,  and  a  number  of 
these  contain  auriferous  detritus,  which  has  been  mined  for  gold. 

Marine  Detritus. — In  some  regions,  the  auriferous  detritus, 
after  being  repeatedly  deposited  and  again  swept  away,  to  be 
re-deposited  further  down  the  valleys,  has  at  last  reached  the 
sea.  The  coast  of  Oregon,  in  western  ISTorth  America,  and 
Vladivostock,  in  southeastern  Siberia,  are  examples.  Here  the 
ebb  and  flow  of  the  tide  operate  very  nearly  on  the  principles 
of  artificial  ore-dressing ;  and  one  would  think  that  a  concen- 
tration of  the  heavier  particles  might  be  thus  effected.  But  it 
does  not  appear  that  such  effects  have  been  recognized  hitherto. 


THE    GENESIS    OF    ORE-DEPOSITS.  157 

Kackar  District,  in  the  Ural. — At  the  beginning  of  this  sec- 
tion, in  the  discussion  of  features  of  auriferous  erosion  detritus, 
some  characteristics  of  the  Ural  placers  were  described.  A 
few  additional  particulars  concerning  them  may  be  of  interest. 
The  gold-bearing  stratum  occurs  at  no  definite  depth.  As  a 
rule,  the  whole  of  the  barren  or  poor  cover  is  stripped  off  and 
thrown  aside,  before  the  auriferous  layer,  thus  laid  bare,  is  sys- 
tematically attacked.  Open  cuts  (Eazregy)  in  the  surface,  of 
greater  or  less  depth,  are  thus  created,  and  are  usually  left  to 
be  filled  up  by  the  rivers.  In  the  district  of  Kackar,  already 
mentioned,  in  the  Southern  Ural,  original  gold-deposits  ("  root- 
deposits  ")  of  gold  have  been  repeatedly  found  in  the  bottom 
of  these  cuts.  They  were  well-defined  quartz-veins,  carrying  in 
the  upper  zone  free  gold,  but  at  greater  depth  sulphides  and 
arsenides  rich  in  gold.  In  the  case  I  have  in  mind,  the  original 
open  cut  extended  for  a  considerable  distance  along  the  strike 
of  the  vein ;  but  the  bed-rock  (which  was  at  the  same  time  the 
country-rock  of  the  vein)  was  much  decomposed,  so  that  the 
difference  between  detritus  and  bed-rock  was  not  strikingly 
evident ;  and  the  placer-working  passed  only  by  gradual  stages 
into  vein-mining. 

Hysteromorphous  gold-deposits  may  thus  be  said,  in  a  gen- 
eral way,  to  occur  in  the  following  positions  : 

1.  In  the  simple  detritus  of  weathering,  immediately  upon 
the  original  deposit  (root-deposit). 

2.  Mixed  with  the  sand  and  gravel  of  present  streams. 

3.  At  certain  points,  in  the  river-bottom,  into  the  crevices 
and  fissures  of  which  the  gold  has  sunk. 

4.  Mixed  with  the   impermeable  material   of  older  water- 
courses, through  which  the  gold  could  not  sink. 

5.  On  the  false  bottoms  or  bed-rocks. 

6.  On  the  true  bed-rock. 

7.  In  the  decomposed  bed-rock  itself. 

In  considering  the  chemical  changes  of  the  outcrops  of  de- 
posits (including,  of  course,  those  which  give  rise  to  hystero- 
morphous  derivatives)  we  have  seen  that  sulphides  suffer  total 
decomposition,  and  that  of  their  constituents  only  the  unoxi- 
dizable  metals,  such  as  gold  and  platinum,  remain  unaffected. 
Silver-ores  and  native  silver,  being  attacked  by  the  chlorides 
of  the  vadose  circulation,  are  consequently  not  found  in  hystero- 


158  THE    GENESIS    OF    ORE-DEPOSITS. 

morphous  deposits.  But  gold  occurring  in  nature  is  for  the 
most  part  alloyed  with  silver.  The  gold  from  the  veins  of  Bud- 
weis,  in  Bohemia,  contains  by  weight  about  two  parts  of  silver, 
and  that  of  Transylvania  contains  by  weight  more  than  three 
of  silver,  to  ten  of  gold.  Whenever  I  have  had  opportunity  to 
compare  the  gold  of  an  original  or  root-deposit  with  that  of  its 
derived  placer,  I  have  found  the  latter  to  be  of  greater  fineness, 
that  is,  to  contain  less  silver.  I  am  strongly  inclined  to  ascribe 
this  phenomenon  to  the  prolonged  contact  with  water  contain- 
ing chlorides.  The  dull  surface  of  placer-gold  and  its  fre- 
quently spongy  interior  structure,  as  compared  with  the  luster 
and  solidity  of  "  quartz-gold,"  favor  this  explanation. 

Platinum-Placers. — Detrital  deposits  of  platinum  have  been, 
until  recently,  particularly  observed  in  the  Ural  only,  from 
which  the  main  supply  of  platinum  was  derived.  Additional 
localities  are  now  reported  in  the  Altai  district  of  Siberia  and 
in  Canada  and  British  Columbia.  In  the  Tulameen  district,  it 
is  said,  the  hydraulic  method  of  mining  has  been  introduced 
for  platinum.  I  have  been  unable  to  obtain  detailed  informa- 
tion concerning  the  features  of  these  deposits. 

In  the  Ural,  and  particularly  in  its  most  productive  district, 
that  of  Niznyj  Tagil,  the  conditions  closely  resemble  those  of 
gold-deposits.  The  richest  platiniferous  layers  are  on  the  true 
bed-rock.  Platinum  and  its  associates,  palladium,  nevjanskite 
and  siserskite,  being  found  to  occur  occasionally  adhering  to 
olivine  and  chromite,  it  was  inferred  that  they  were  derived 
from  the  serpentine,  which  is  itself  a  secondary  product  from 
olivine-rocks.  More  recently,  platinum  is  said  to  have  been 
found  in  an  olivine-gabbro  not  yet  metamorphosed;  but  whether 
the  metal  is  a  primary  or  an  exotic  constituent,  can  as  yet 
scarcely  be  declared  with  certainty. 

Formerly  no  other  occurrence  of  platinum  than  the  native 
metal  was  known;  but  now  a  platinum-ore  has  been  found  in 
the  Sudbury  district,  Canada,  namely,  sperrylite,  a  compound 
of  platinum  and  arsenic.  Since  this  is  certainly  xenogenous, 
the  question  as  to  the  original  sources  of  platinum-deposits  is 
advanced  to  a  new  phase  by  its  discovery. 

Tin-Placers. — In  connection  with  the  occurrence  of  tin  as 
cassiterite  in  detrital  deposits,  the  specific  gravity  (6.97)  of  this 
mineral,  nearly  equalling  that  of  iron,  and  the  great  resistance 


THE    GENESIS    OF    ORE-DEPOSITS.  159 

which  it  offers  to  natural  agents  of  decomposition,  doubtless 
play  the  principal  part.  Of  the  numerous  and  various  associates 
of  cassiterite  in  its  original  deposits,  none,  except  quartz,  are 
equally  able  to  resist  decomposition ;  and  the  consequence  is, 
that  the  detritus,  both  of  weathering  and  of  erosion,  from  the 
outcrops  of  such  deposits,  contains,  besides  the  products  of  the 
decomposition  of  these  other  minerals,  chiefly  quartz  and  pieces 
of  cassiterite.  The  latter,  by  reason  of  its  high  specific  gravity, 
will  tend  to  sink  through  the  lighter  detritus  and  be  concen- 
trated near  the  bed-rock. 

The  stanniferous  detrital  deposits  of  Bohemia  and  Saxony, 
as  well  as  Cornwall,  were  long  since  exhausted ;  those  of  Aus- 
tralasia, the  South  Sea  islands  and  South  America  are  still 
worked.  According  to  the  special  monograph  of  Dr.  E.  Reyer,* 
the  richest  layers  are  in  fact  found  at  the  bottom  of  the  detritus, 
immediately  on  the  bed-rock. 

With  regard  to  the  geological  age  of  the  detrital  tin-deposits, 
the  rule  stated  for  gold  generally  obtains,  namely,  they  are  for 
the  most  part  diluvial,  yet  have  sometimes  been  formed  in  earlier 
periods.  Thus,  at  Flatten,  in  Bohemia,  a  tin-placer,  which  has 
been  worked  under  a  bedded  flow  of  basalt,  and  the  detrital 
deposits  of  Annaberg  in  Saxony,  which  underlie  the  basalt  of 
the  Scheibenberg,  were  doubtless  formed  in  Tertiary  times. 

The  original  or  root-deposits  of  tin  have  been  hitherto  quite 
generally  considered  as  very  old  formations,  connected  with 
the  eruptions  of  granite  and  felsite-porphyry. 

Recently,  however,  tin  has  been  found  in  the  Mesozoic  lime- 
stones of  Campiglio  Maritima;  and  it  has  been  shown,  more- 
over, that  the  root-deposits  of  tin  in  Mexico  and  Bolivia  occur 
in  trachytes  and  andesites,  erupted  during  the  Cretaceous  or 
Eocene.  Dr.  A.  W.  Stelzner  has  recently  published  a  notice 
of  the  latter  occurrence,f  and  promised  a  more  elaborate  de- 
scription. He  says  (p.  533) : 

"The  part  played  in  geological  history  by  the  tin-ore  of  Bolivia  contrasts 
sharply  with  that  which  has  been  observed  in  the  Erzgebirge  of  Saxony  and 
Bohemia,  and  in  Brittany,  Cornwall,  East  India,  Australia,  Tasmania,  and  the 
United  States  of  America,  and  which  has  hitherto  been  willingly  regarded  as  the 
exclusive  method  of  tin-occurrence.  The  Bolivian  tin-ore  does  not  constitute 

*  Zinn,  eine  geol.-monlan.-historische  Monographic,  Berlin,  1881,  p.  208. 
t  Zeitsch.  d.  deutsch.  geol.  Gesellsch.,  xliv.,  1892,  p.  531. 


160  THE    GENESIS    OF    ORE-DEPOSITS. 

aureoles  surrounding  plutonic  granite,  and  characterized  by  the  contemporaneous 
presence  of  minerals  containing  boron  and  fluorine.  On  the  contrary,  it  can  only 
be  considered  as  produced,  simultaneously  with  precious  silver-ores  and  sulphides 
of  copper,  iron,  lead  and  zinc,  by  precipitation  from  mineral  springs,  which  were 
connected  in  point  of  time,  and  perhaps  also  as  effects,  with  outflows  of  Cretaceous 
or  Lower  Tertiary  volcanic  rocks." 

c.  Hyster amorphous  Deposits  of  the  Older  Geological  Formations. 

Twenty-five  years  ago,  at  a  time  when  no  deposits  of  this 
kind  were  known,  in  an  article  on  the  continuance  of  ore-de- 
posits (especially  of  gold)  in  depth,*  I  prophesied  their  dis- 
covery. They  have  since  been  observed  in  different  gold-dis- 
tricts. I  refer  to  the  characteristic  secondary  deposits  in  quartz 
conglomerates,  indicated  by  their  stratigraphical  positions  and 
their  contained  fossils  to  be  of  considerable  geological  age. 
Such  occurrences  are  often  called  simply  cement-beds,  as  are 
the  conglomerates  of  cemented  gravel  in  recent  placers ;  and  it 
is  difficult  in  cases  where,  as  in  Australia,  this  term  is  frequent,! 
to  infer  the  age  of  the  corresponding  conglomerates.  It  is, 
however,  in  some  cases  unquestionable  that  these  cements 
actually  represent  old  formations — chiefly  Palaeozoic — and  are 
therefore  hysteromorphic  products  from  still  older  primitive 
deposits. 

Deadwood,  South  Dakota. — One  of  the  best  described  occur- 
rences is  that  of  Deadwood  and  Blacktail  gulches,  in  the  Black 
Hills  of  Dakota.  J  It  is  a  conglomerate  bed,  passing  upwards 
into  sandstone,  and  belonging,  according  to  the  contained  fos- 
sils, to  the  Potsdam  sandstone  (Cambrian).  It  is  by  no  means 
a  river-deposit ;  on  the  contrary,  the  fossils  indicate  a  shallow 
marine  basin.  The  series  lies  very  flat  upon  crystalline  schists ; 
is  at  most  100  feet  (30  meters)  thick,  and  is  covered  by  a  layer 
of  porphyry,  which  has  most  probably  protected  it  from  ero- 
sion. Fig.  100,  a  section  given  by  Mr.  Devereux  (1.  <?.,  p.  468), 
shows  how  the  deposit  is  exposed  and  rendered  accessible  on 
the  sides  of  Deadwood  and  Blacktail  gulches,  which  cut  through 
into  the  underlying  schists. 

The  conglomerates  of  pebbles  of  quartz,  schist,  and  hema- 

*  Oesterr.  Zeitsch.  f.  B.  u.  H.  wesen,  xv. ,  1867. 
f  See,  for  example,  Mr.  Lock's  Gold,  etc.,  already  cited. 

J  W.  B.  Devereux,  "  The  Occurrence  of  Gold  in  the  Potsdam  Formatio  n,  Black 
Hills,"  Trans.  A.  L  M.  E.,  1882,  x.,  465. 


THE    GENESIS    OF    ORE-DEPOSITS.  161 

tite  which  lie  at  the  base  of  this  Cambrian  series  carry  partly 
coarse  gold,  under  such  circumstances  that  there  can  be  no 
doubt  of  its  secondary  origin.  It  came  probably  from  the  Home- 
stake  vein  near  by.  The  auriferous  detritus  is  about  2  meters 
(6.6  feet)  thick,  and  the  portions  next  to  the  underlying  rock 
are  the  richest ;  so  we  have  here  the  relation  of  the  "  true  bed- 
rock." If  my  theory  be  correct,  that  the  gold  reached  this 
position  by  sinking  through  the  lighter  detritus,  it  might  be 
said  that  the  gold  was  deposited  not  with,  but  after,  the  detritus, 
and  consequently  that  the  Cambrian  fossils  do  not  prove  the 
Cambrian  age  of  the  gold-deposition.  Such  an  objection  might 
perhaps  have  weight  in  other  cases  of  the  kind,  but  in  this  case, 
the  bed  being  covered  by  a  porphyry  overflow,  and  hence  not 
at  all  exposed  to  later  deposits,  the  objection  has  no  force. 

The  Black  Hills  contain  representatives  of  the  three  principal 
types  of  gold-occurrence,  namely,  gold-bearing  veins  and  ancient 
and  recent  detrital  deposits.  The  paper  of  Mr.  Devereux  is 
also  very  interesting  in  other  respects — for  instance,  with  re- 
gard to  the  explanation  of  the  differing  fineness  of  vein-  and 
detrital-gold,  and  with  regard  to  the  traces  of  chemical  action 
in  the  detrital  deposits. 

Australasia. — The  data  from  Australasia  concerning  this  class 
of  deposits  are  less  conclusive.  In  1876  Wilkinson  observed 
in  the  Talhawang  district  of  New  South  Wales  that  the  Tertiary 
detrital  deposits  received  their  gold  from  Carboniferous  con- 
glomerates. These  conglomerates  were  associated  with  sand- 
stones and  slates,  in  which  occurred  a  fossil  plant  peculiar  to 
the  Carboniferous  of  New  South  Wales.  The  gold  occurred  in 
pretty  coarse,  rounded  grains,  and  on  one  occasion  a  nugget 
was  found  weighing  5  ounces  (155  grammes).  Similar  condi- 
tions are  said  to  obtain  in  the  Hawkesbury  rocks,  at  the  North 
Shore,  Sydney,  at  Govett's  Leap,  and  in  the  conglomerates  of 
the  Coal-Measures  in  the  southern  district.  Gold  is  also  re- 
ported in  the  Coal-Measures  at  Peak  Downs  in  Queensland, 
near  Hobart  Town  in  Tasmania,  and  in  New  Zealand.* 

The  question,  whether  these  deposits  of  gold  were  really 
made  simultaneously  with  that  of  the  detritus  in  the  Carbon- 

*  Lock's  Gold,  etc.,  pp.  515,  516.  See  also  K.  DaubreVs  "Note  on  Certain 
Modes  of  Occurrence  of  Gold  in  Australia,"  Quart.  Jour.  Geol.  Soc.,  1878,  xxxiv., 
p.  435. 


162  THE    GENESIS    OF    ORE-DEPOSITS. 

iferous  period,  may  be  decided  by  the  circumstance  that  the 
conglomerates  are  or  are  not  covered  by  Carboniferous  strata. 
In  the  latter  case,  it  is  possible  that  the  gold  may  have  sunk 
into  the  gravel  at  a  later  period. 

South  Africa. — In  South  Africa,  at  Witwatersrand  in  the 
Transvaal,  ancient  detrital  deposits  have  yielded  a  considerable 
gold-production.  According  to  E.  Cohen,*  the  Witwatersrand 
consists  of  sandstones  (which  resemble  closely  that  of  Table 
mountain  at  the  Cape  of  Good  Hope)  and  dolomites  of  high 
age — undoubtedly  Palaeozoic.  Conglomerates  of  the  same  age, 
intercalated  among  these  strata,  occur  in  the  vicinity  of  Johannes- 
burg in  several  nearly  parallel  outcrops,  and  are  for  certain  dis- 
tances tolerably  rich  in  gold.  They  are  composed  mostly  of 
quartz  pebbles,  sometimes  with  fragments  not  entirely  rounded, 
which  are  united  by  a  strong,  ferruginous,  arkose-like  cement. 
The  quartz  pebbles  are  sometimes  porous  and  impregnated  with 
hydrated  ferric  oxide,  thus  presenting  the  peculiar  corroded 
appearance  so  characteristic  of  auriferous  quartz.  The  gold 
occurs  chiefly  in  the  cement,  immediately  next  to  the  pebbles. 
It  is  mostly  coarse-grained,  and  sometimes  even  crystalline. 
The  latter  circumstance  has  raised  the  question  whether  the 
gold  has  not  here  been  chemically  precipitated,  and  hence, 
whether  these  are  detritus-deposits  at  all.  My  standpoint  in 
this  discussion,  as  I  have  remarked  at  the  end  of  the  section  on 
chemical  effects  in  the  upper  region,  is  like  that  of  E.  Cohen. 
I  do  not  deny  the  presence  of  chemical  influences  in  the  de- 
trital deposits,  although  I  have  personally  not  happened  upon 
them.  So  far  as  I  can  judge  from  the  treatises  of  A.  R.  Saw- 
yerf  and  Charles  A.  Alford, %  and  from  a  specimen  of  the  Wit- 
watersrand conglomerate,  kindly  sent  to  me  by  A.  H.  Haider, 
of  Pietersburg,  it  is  my  opinion  that  the  gold  was  mechanically 
brought  into  the  conglomerates  from  still  older  auriferous 
quartz-veins  occurring  in  the  rocks  which  form  the  basis  of 
this  Palaeozoic  formation ;  and  since  the  idea  of  a  later  entrance 
of  the  gold  is  excluded  by  the  almost  vertical  position  of  the 

*  "  Goldfuhr  Conglom.  in  Sudafrika."  Mitth.  d.  naturw.  Ver.  f.  Neupom- 
mern,  etc. 

f  "The  Witwatersrand  Gold-field."  Trans.  N.  StaffordsL,  Inst.  M.  and  Mech- 
E.,  1839. 

J  Geological  Features  of  the  Transvaal,  London,  1891. 


THE   GENESIS    OF   ORE-DEPOSITS.  163 

conglomerate  beds  near  Johannesburg,  I  suppose  the  gold  to 
have  been  deposited  at  the  same  time  as  the  detritus.  The 
greater  part  of  the  gold,  as  has  been  said,  occurs  in  the  cement. 
There  are  no  vein-like  deposits  whatever  in  the  conglomerate ; 
and  the  only  chemical  changes  which  could  be  presumed  are 
confined  to  the  decomposition  of  pyrites  and  the  segregation 
of  its  contained  gold. 

According  to  a  foot-note  in  Phillips's  Treatise  on  Ore-De- 
posits (p.  2),  gold  is  washed  out  of  granular  conglomerates  of 
the  Lower  Carboniferous  at  Besseges,  Department  du  Gard, 
France. 

Bohemia. — In  the  region  of  Trautenau,  in  Bohemia,  I  ob- 
served at  Gabersdorf  and  Goldenols  considerable  traces  of  an- 
cient placer-mining,  partly  in  the  valley-bottom,  partly  on  the 
slope,  which  consisted  of  old  Permian  and  Carboniferous  con- 
glomerates. These  remains  looked  exactly  like  other  gold- 
workings  in  Bohemia,  and  I  could  only  explain  their  situation 
by  supposing  that  this  was  another  case  of  auriferous  Palaeozoic 
detritus.  The  same  may  be  said  of  another  enigmatical  gold- 
occurrence,  at  Stupna  in  Bohemia,  where  in  1593  a  gold  of  un- 
usual fineness  (0.954)  for  Bohemia  was  produced,  and  must 
have  come  from  a  detrital  deposit.  The  ancient  miners  pene- 
trated through  bedded  flows  of  melaphyre.  The  waste-dumps 
are  composed  of  pebbles  from  Permian  conglomerates.  It  is 
therefore  possible  that  these  mines  were  operated  upon  aurif- 
erous Permian  conglomerates.* 

*  F.  Posepny,  "Ueber  einige  wenig  bekannte,  alte  Goldbergbaue  Bohmens." 
Oesterr.  Zeitsch.  /.  Berg.  u.  H.-wesen,  xxxvii.,  1889. 


11 


DESCRIPTION  OF  FIGURES. 

FIG.  1. — Erosion  of  a  channel  in  rock-salt,  at  Maros  Ujvar, 
Transylvania.  I,  impermeable  rock;  S,  rock-salt;  H,  hydro- 
static head  of  vadose  circulation. 

FIGS.  2  and  3. — Course  of  vadose  circulation,  as  affected  by 
the  nature  of  the  rocks.  S,  soluble,  I,  insoluble  rock ;  H,  hydro- 
static head ;  a,  entrance ;  2,  outlet ;  a  b  c  z,  natural  curve  of 
water-circulation,  if  I  did  not  intervene ;  a  d  z,  actual  path 
under  or  over  I. 

FIG.  4. — Geode  of  Eisenopal  (jasp-opal),  showing  the  filling 
of  a  cavity  in  which  air  or  gas  is  present,  besides  .the  liquid. 

FIG.  5. — Diagrammatic  representation  of  deposits  in  a  lime- 
stone cavern.  (Deposits  white;  empty  space,  black.) 

FIG.  6. — Division  of  ground-water  by  fissures  and  permeable 
strata. 

FIG.  7. — Conventional  representation  of  an  artesian  well. 

FIG.  8. — Spring-mounds  at  Arczo  near  Korond,  in  Transyl- 
vania. 

FIG.  9. — Upward  erosions  in  building-stone  in  the  walled  pit 
of  a  spring  at  Bourbonne-les-Bains. 


Fig,  I 


JUaros 


DESCRIPTION  or  FIGURES. 

FIG.  10. — Deposition  of  cinnabar  and  opal  in  basalt  at  Sul- 
phur Bank,  Cal.  Sketch  at  the  surface  by  F.  Posepny. 

FIG.  11. — Similar  deposition  at  the  same  mine,  in  sandstone, 
at  greater  depth  (J.  Le  Conte). 

FIG.  12. — Carlsbad  Spruddstein. 

FIG.  13. — Pisolite  with  pyrite  crusts,  from  Hammam  Mesou- 
tine. 

FIGS.  14,  15  and  16. — Pisolites  formed  by  dripping  solutions 
at  Off'enbanya. 

FIG.  17. — Sphere-ores,  a  correction  of  the  illustrations  of 
Cotta  (Erzl.  Lehre,  L,  33)  and  Daubree  (Les  eaux  aux  epoques 
anciennes,  p.  64). 

FIG.  18. — Gold  specimen  from  the  Katrontza  ore-body,  Yeres- 
patak. 

FIG.  19. — A  crusted  rock-nucleus,  from  Raibl. 

FIG.  20. — Boiler-scale. 

FIGS.  21  and  22. — Fragments  of  rock  and  older  crusts,  sur- 
rounded by  later  crusts,  from  Zellerfeld  (J.  C.  L.  Schmidt). 

FIG.  24. — Gold-aggregates,  surrounded  by  crusts  of  calcite, 
rhodonite,  siderite  and  quartz,  from  the  Rakosi  Mangan  ore- 
body,  Yerespatak. 


Fig.22 


Bradley  4  PtxUet,  Enffr't,.ff.f. 


DESCRIPTION  OF  FIGURES. 

FIGS.  25,  26,  27  and  28. — Sections  of  stalactites  of  galena, 
blende  and  pyrite,  so-called  "  pipe-ores,"  with  hollow  axis,  from 
Raibl. 

FIG.  29. — Section  of  rhodonite  stalactites,  with  axis  of  gold- 
aggregates,  from  the  Hungarian  National  Museum. 

FIG.  30. — View  of  the  same. 

FIG.  31. — Section  of  a  similar  stalactite  in  the  author's  pos- 
session, from  the  Rakosi  Mangan  ore-body.  Enlarged  to  twice 
the  natural  size. 

FIGS.  32,  33,  34,  35. — Sections  of  ore-channels  in  the  lime- 
stone of  the  Valle  mines,  Missouri  (J.  R.  Gage). 


DESCRIPTION  OF  FIGURES. 

FIG.  36. — Plan  showing  gold-bearing  veinlets,  striking  E.  to 
"W.,  in  granite  (berezite)  striking  N".  to  S.,  at  Berezov. 

FIG.  37. — Network  of  veins  and  vein-clay-slates  in  the  Claus- 
thal  district.  Localities:  #,  Lautensthal;  b,  Bockwiese ;  c, 
Festenberg ;  d,  Ober-Schulenberg ;  e,  Wildemann ;  /,  Zeller- 
feld;  </,  Clausthal. 

FIG.  38. — Network  of  veins  and  Ruschel  in  the  St.  Andreas- 
berg  district.  Ruschel :  a  6,  Neufang;  a  c,  Edellent;  dfe,  Sil- 
berberg ;  f  g  h,  Abendroth  Veins  :  1 1,  Samson  (i,  Samson  shaft); 
k  k,  Bergmannstrost. 

FIG.  39. — Section  through  the  Franz  Josef  shaft,  Przibram, 
Bohemia.  A  B,  sea-level,  heights  above  and  below  which  are 
given  in  meters  on  the  left.  The  Roman  numerals  on  the  right 
indicate  the  vein-levels,  a,  post-Cambrian  slates ;  6,  Cambrian 
sandstone ;  c  c,  faulted  stratum  of  adinole ;  d  d,  diorite  dikes ; 
m,  Martyr  vein ;  u  u,  Marie  Hilf  vein  ;  v  v  v,  Sefcin  vein ;  w  w, 
West-dipping  vein ;  s  5,  Franz  Josef  shaft. 


Bradley  $  -H«jte«,  Engr's,  A.  f, 


DESCRIPTION  OF  FIGURES. 

FIG.  40. — Ideal  section  through  Bohutin,  near  Przibram.  a, 
Cambrian  sandstone ;  6,  pre-Cambrian  schists ;  c,  granite ;  d, 
main  fault-fissure ;  e  e,  diorite  dikes.  (NoTE  :  At  Przibram  it- 
self the  pre-Cambrian  schists  constitute  the  hanging-wall  of  the 
main  fault-fissure  to  the  entire  depth  of  the  mines — about  1100 
meters,  or  3600  feet.) 

FIG.  41. — Diagrammatic  representation  of  the  structure  of 
the  Yerespatak  ore-bodies  (Volbura),  showing  the  ore  replacing 
the  washed-out  cement  of  a  breccia,  mostly  of  porphyritic  frag- 
ments. 

FIG.  42. — The  same,  only  conglomerate  instead  of  breccia. 

FIG.  43. — Vertical  S.  to  !N".  section  through  the  Yulkoj  mines, 
showing  the  supra-position  of  andesite  upon  the  shaly  sand- 
stone, a  a,  Nepomuk  adit ;  6,  sandstone  ;  <?,  andesite  ;  d,  Cora- 
bia  open-workings  ;  e,  Jeruga  adit ;  /,  Peter-Paul  adit ;  #,  Her- 
mann adit. 

FIG«.  44. — Vertical  E.  to  W.  section  through  the  gold-mines 
of  Botesiu  and  Vulkoj.  A,  Botesiu;  B,  Vulkoj  ;  a,  Fepomuk 
adit ;  6,  sandstone ;  c,  andesite ;  d,  Corabia  open-workings ;  j9 
Jeruga  vein. 


Fig.  40 


Fig.  41 


Fig.  43 


Bradley  cfi^bafc*,  An^rr'a, 


DESCRIPTION  OF  FIGURES. 

FIG.  45. — Section  in  fourth  level  of  Peter  Stehend  vein,  Frei- 
berg, a,  decomposed  country-rock ;  6,  quartz,  with  brown-spar, 
pyrites,  blende,  and  silver-ores.  (G.  A.  Yon  Weissenbach,  No. 
2  in  his  work.) 

FIG.  46. — Section  on  third  level  of  Adlerfliigel  Stehend  vein, 
Freiberg,  a,  gneiss  fragments ;  6,  older  vein-formation  ;  c9  later 
quartz-vein  matter;  d,  gneiss.  (Weissenbach,  "No.  21  in  his 
work.) 

FIG.  47. — Section  on  third  level  of  Gnade  Gottes  Stehend 
vein,  Freiberg.  (Weissenbach,  No.  22.) 

FIG.  48. — Section  on  thirteenth  level  of  Adalbert  Liegend 
vein,  Przibram.  a,  galena  and  calcite ;  b  (or,  more  precisely, 
the  irregular  mass  shown  to  the  right  of  6),  zinc-blende ;  c,  sand- 
stone. (J.  Zadrazil,  No.  52.) 

FIG.  49. — Section  on  thirteenth  level  of  Adalbert  master- 
lode,  Przibram.  a,  siderite ;  b,  calcite ;  c,  quartz ;  d,  galena ; 
e,  diorite.  (J.  Zadrazil,  No.  5.) 

FIG.  50. — Section  on  twenty-ninth  level  of  Adalbert  master- 
lode,  Przibram.  a,  calcite ;  b,  silicified  (verquarzte)  vein-matter ; 
c,  quartz;  d,  diorite.  (J.  Zadrazil,  No.  21.) 

FIG.  51. — Section  on  adit  of  Hildebrand  vein,  Joachimsthal. 
a,  mica-slate ;  6,  dolomite ;  c  c,  proustite ;  d,  dolomite  with 
pyrite;  e,  uranite.  (J.  Nemecek,  No.  11.) 

FIG.  52. — Section  on  tenth  level  of  Junghauerzechen  vein, 
Joachimsthal.  a  a,  dolomite  and  calcite ;  b  6,  mica-schist ;  c, 
basalt-wacke ;  d,  chalcopyrite ;  e,  prousite.  (J.  Nemecek,  No.  5.) 


Fig.  45 


Fig.  46 


.Fig,.  47 


Fig.  49 


Fig.  48 


Fig.  51 


Fig.  52 


JBr,adl»v3  Poattt,  Engr'i,  X.f^ 


DESCRIPTION  OF  FIGURES. 

FIG.  53. — Specimen  from  the  Drei  Prinzen  Spat  vein,  in  the 
eighth  level  of  the  Churprinz  Friedrich  August  mine,  Freiberg, 
Saxony ;  ^  nat.  size ;  a,  quartz  with  disseminated  galena  and 
blende,  indistinctly  crustified — from  the  older  vein ;  &,  fluorite 
with  quartz ;  c,  barite  in  thin  crusts ;  d,  gray  earthy  mass  of  the 
later  vein,  very  distinctly  crustified;  e,  the  latest  fault  fissure. 

FIG.  54. — Copper-deposit  at  Prettau  in  Tyrol.  Sketch  of  the 
roof  the  Ottilie  level. 

FIG.  55. — Ditto;  side  of  the  same  level. 

FIG.  56. — Ditto ;  vertical  section  in  the  plane  of  the  pitch, 
which  descends  nearly  westward,  the  course  of  the  strata  being 
E.  to  W.,  and  the  dip  steep  to  South.  Adits  and  levels :  a,  Peter ; 
6,  Jacob ;  c,  Marx ;  d,  Johann ;  e,  Kristof ;  /,  Mkolaus ;  </,  Ignatz. 
The  three  levels  below  g  are  the  Ottilie,  Karl,  and  Hugo. 

FIG.  57. — Ditto;  horizontal  projection,  showing  approximately 
the  position  of  the  ore-bodies  on  the  different  levels ;  a  to  g  as 
in  Fig.  56 ;  x  y,  strike ;  y  10,  true  dip  of  strata ;  y  z,  pitch  of  ore- 
shoot. 


DESCRIPTION  OF  FIGURES. 

FIG.  58. — Surface-geology  of  the  vicinity  of  the  Comstock 
lode.  B,  basalt;  L  H  A,  later  hornblende-andesite ;  A  A,  au- 
gite-andesite ;  E  H  A,  earlier  hornblende-andesite ;  L  D  6,  later 
diabase  (black  dike) ;  E  D  6,  earlier  diabase ;  Q  P,  quartz-por- 
phyry ;  M  D  r,  metamorphosed  diorite ;  P  D  e,  porphyritic  dio- 
rite;  G  D  r,  granular  diorite;  M,  metamorphic  rocks;  G,  gran- 
ite. (G.  F.  Becker.) 

FIG.  59. — Vertical  cross-section  through  Union  shaft.  (G.  F. 
Becker.) 

FIG.  60. — Vertical  cross-section  through  C.  and  C.  shaft.  (G. 
F.  Becker.) 

FIG.  61. — Vertical  cross-section  through  Yellow  Jacket  shaft. 
(G.  F.  Becker.) 

FIG.  62. — Vertical  cross-section  through  Belcher  shaft.  (G. 
F.  Becker.) 

FIG.  63. — Vertical  section  on  line  of  Sutro  tunnel.  I,  II,  III, 
and  IV,  Sutro  tunnel  shafts ;  s  s,  lines  of  solfataric  action ;  v, 
vein-material.  (G.  F.  Becker.) 


DESCRIPTION  OF  FIGURES. 

FIG.  64. — Vertical  E.  and  W.  section  through  the  mines  of 
Yalle  Sacca,  near  Rezbanya,  Hungary,  a,  sandstone ;  6,  Juras- 
sic limestone ;  c,  Liassic  limestone ;  d  d,  crystalline  limestone ; 
c,  syenite;/,  3d  adit;  #,  4th  adit;  A,  new  Anton  adit;  i,  Juliana 
ore-body ;  k,  Marianna  ore-body ;  I,  Anton  ore-body ;  m  m,  par- 
allel intercalated  dike ;  n  n,  Reichenstein  ore-body ;  o  o,  dikes. 

FIG.  65. — Vertical  longitudinal  section  of  Reichenstein  ore- 
body,  Valle  Sacca,  Hungary,  n  n,  ore-body ;  6,  limestone ;  d,  1st 
adit;  e,  2d  adit;  /,  3d  adit. 

FIG.  66. — Diagram  showing  the  S.  "W.  pitch  of  the  Reichen- 
stein ore-body,  the  dikes  dipping  W.  x  y,  course  of  dikes ;  x 
w,  dip  of  dikes ;  x  z,  pitch  of  ore-shoot. 

FIG.  67. — Vertical  N*.  and  S.  cross-section  of  the  Government 
mine  at  Raibl,  Carinthia.  a,  Raibl  slates ;  6,  ore-bearing  lime- 
stone. Adits :  c9  Johann ;  d,  Frauen ;  e,  Sebastian ;  /,  Franz 
II.,  IV.,  VI.  and  VII. ;  positions  of  levels  numbered  upwards 
from  Johann  adit.  » 

FIG.  68. — Vertical  N".  and  S.  section  through  the  Struggl  mine 
at  Raibl.  a.  slate ;  6,  ore-bearing  limestone ;  /,  Franz  adit ;  g, 
Einsiedl  level. 

FIG.  69.— Faulting  of  the  contact  by  a  "  Blatt."  a,  slate ;  6, 
limestone. 

FIG.  70. — Vertical  N.  and  S.  cross-section  through  the  Benyes 
mine,  Rodna,  Transylvania,  a,  mica  slate;  6,  andesite;  c,  lime- 
stone. Adits :  d,  Amalia ;  e,  Zap  Peter ;  /,  Anton ;  g,  Nepo- 
muk;  A,  Teresia. 

FIG.  71. — Section  through  the  "New  Lead-Mass,"  in  Mt. 
Ambree,  Offenbanya,  Transylvania,  a,  mica-slate ;  6,  andesite ; 
c,  limestone.  Levels :  d,  Segen  Gottes ;  e,  Gluck  auf ;  /,  ore- 
shoot. 


Ejradfey  f  f^xitf»t  lsmgr*>  • 


DESCRIPTION  or  FIGURES. 

.  72. — Face  of  level  on  the  Josephiblatt,  at  Raibl,  where 
the  ores  occur  in  the  country-rock. 

FIG.  73. — Vertical  E.  and  "W.  section  through  the  McKean 
shaft,  Iron  Hill,  Leadville,  Colo.  W.  P.,  white  porphyry;  B. 
L.,  hlue  limestone;  G-.  P.,  gray  porphyry;  W.  L.,  white  lime- 
stone; L.  Q.,  lower  quartzite;  GL,  Granite.  (A.  A.  Blow.) 

FIG.  74. — Sections  from  the  Red  Mountain  district,  Colo. 
A.,  andesite;  P.  Q.,  pink  quartzite ;  L.,  limestone;  L.  Q.,  lower 
quartzite ;  a,  Batavia  shaft ;  a  6,  Jackson  tunnel ;  c,  adit ;  o  o,  ore. 
(G-.  E.  Kedzie.) 

FIG.  75. — Section  across  Longfellow  Hill  and  Chase  Creek, 
Clifton  district,  Arizona.  A,  Longfellow  Hill ;  B,  Chase  Creek ; 
a  a,  felsite ;  6,  limestone ;  c,  sandstone ;  d,  porphyry ;  e,  upper 
adit ;  /.  deep  adit.  (A.  F.  Wendt.) 

FIG.  76. — Ideal  sections  at  Eureka,  Nevada.  A,  Ruby  Hill ; 
a,  Prospect  Mountain  quartzite ;  6,  crushed  limestone ;  c,  lime- 
stone ;  d,  shale ;  e,  stratified  limestone ;  /,  Secret  Canon  shale ; 
g,  Hamburg  limestone;  i,  Logan  shaft;  p,  Lawton  shaft.  (J. 
S.  Curtis.) 

FIG.  77. — Combined  section  at  Eureka  for  comparison  with 
Fig.  76.  a,  ft,  c,  d,  e,  /,  as  above ;  A:,  Windsail  shaft ;  I,  Bell  shaft ; 
m,  Richmond  shaft;  xy,  east  ore-body;  VII. ,  Richmond  7th 
level.  (J.  S.  Curtis.) 

FIG.  78.— Sketch  of  face  of  310-foot  level.  Old  Telegraph 
mine,  Utah,  showing  texture  of  the  filling  (altered  to  cerussite). 
a,  hanging-wall  clay  ;  6,  quartz ;  c,  quartzite. 

FIG.  79. — Section  from  the  lead-region  of  Wisconsin,  in  the 
neighborhood  of  Dubuque,  Iowa.  (J.  D.  Whitney.) 


DESCRIPTION  OF  FIGURES. 

FIG.  80. — Plan  of  ore-deposits  at  Wallerfangen  and  St.  Avoid, 
near  Saar  Louis.  (C.  Simon.) 

FIG.  81. — Cross-section  of  81.  H,  hanging-wall;  F,  foot- 
wall. 

FIG.  82. — Cross-section  of  the  Mechernich  deposits,  showing 
irregular  faulting  of  the  Knoten  sandstone  beds. 

FIG.  83. — Cross-section  of  the  Yesuv  mine,  Freihung,  Bavaria, 
a,  Keuper  clay ;  6,  variegated  sandstone ;  c,  ore-beds ;  d,  engine- 
shaft. 

FIG.  84. — Section  of  a  tree-stem,  replaced  with  galenite,  from 
Freihung. 

FIG.  85. — Calamine  veinlets  in  the  limestone  at  Raibl;  a, 
limestone. 

FIG.  86.— Cellular  calamine  of  Eaibl. 

FIG.  87. — Section  through  the  Laurium  district,  Greece ;  «, 
limestone;  6,  schist;  c,  Hilarion  shaft.  (A.  Cordelia.) 

FIG.  88. — Section  through  the  Laurium  district ;  a,  limestone ; 
by  schist ;  d,  porphyry  dikes.  (A.  Huot.) 

FIG.  89. — Limonite-deposit  in  West  Cumberland ;  a,  millstone 
grist ;  6,  mountain  limestone ;  c,  Silurian  schist.  Hematite  in 
place.  (J.  D.  Kendall.) 

FIG.  90. — Bohneisenstein-deposit  of  Wochein,  Carniola;  a, 
limestone;  6,  iron-ore.  (A.  v.  Morlot.) 


DESCRIPTION  OF  FIGURES. 

FIG.  91. — Tin-vein  in  Cornwall,  with  pseudomorphs  of  cas- 
siterite  after  feldspar  in  the  granite  country-rock.  (C.  Le  Neve 
Foster.) 

FIG.  92. — Tin-vein  in  Cornwall,  showing  "  capel "  or  altered 
"  killas  "  country-rock.  (C.  Le  Neve  Foster.) 

FIG-.  93. — Impregnation  of  the  granite  with  tin-ore  at  East 
Wheal  Lovell,  Cornwall.  (C.  Le  Neve  Foster.) 

FIG.  94. — Specimens  of  ore  from  the  Kongens  mine  at  Roras, 
Norway.  (Th.  Kjerulf.) 

FIG.  95. — Specimen  of  ore  from  the  Mug  mine,  Trondhjem, 
Norway ;  a,  pyrrhotite ;  6,  mica ;  c,  quartz ;  d,  chalcopyrite. 
(Th.  Kjerulf.) 

FIG.  96. — Polished  section  of  ore  from  Ammeberg,  Sweden. 

FIG.  97. — Ditto,  showing  leaf-silver  in  fissures  in  zinc-blende. 

FIG.  98. — Section  through  the  Copper  Falls  mine,  Lake  Su- 
perior ;  a,  trap ;  6,  ash-bed  at  depth  of  80  feet ;  c,  amygdaloid ; 
d,  sandstone  at  depth  of  420  feet. 

FIG.  99. — Nagynyerges  vein  at  Kisbanya,  Transylvania. 

FIG.  100. — Section  through  Palaeozoic  detrital  gold-deposit  of 
the  Black  Hills ;  a,  porphyry ;  6,  schist ;  d,  Potsdam  (old  con- 
tact-lines dotted) ;  e,  cement-mines ;  ff,  placers,  the  one  on  the 
left  in  the  drawing  being  in  Deadwood  gulch  at  Central  City ; 
the  one  on  the  right,  in  Blacktail  gulch.  (Devereux.) 


188  THE    GENESIS    OF    ORE-DEPOSITS. 


Discussion  at  the  Chicago  Meeting,  August,  1893,  Including 
Communications  Subsequently  Received. 

"W.  P.  BLAKE,  Shullsburg,  Wis. :  I  desire  to  express  my  ad- 
miration of  Prof.  Posepny 's  memoir,  and  particularly  of  the 
charming  manner  and  spirit  of  the  introduction. 

With  respect  to  his  mention  of  the  ore-deposits  of  Missouri 
and  Wisconsin,  reference  may  be  made  to  my  paper  presented 
at  this  meeting  (Trans.,  xxii.,  621),  showing  the  existence  of 
dislocations  and  breaks  in  the  bedding,  and  their  apparent  close 
relation  with  the  localization  of  the  ore-deposits  as  claimed  by 
Dr.  James  Gr.  Percival,  and  also  so  claimed  by  Dr.  Jenney  in 
his  paper  before  us  (Trans.,  xxii.,  171).  I  have  in  my  paper 
given  reasons  for  believing  that  the  zinc-  and  lead-ores  in  the 
strata  above  the  compact  Trenton  limestones  were  formed  by 
lateral  secretion  and  concentration  from  above  downwards,  sub- 
stantially as  shown  by  Prof.  J.  D.  Whitney,  and  not  by  the 
ascent  of  solutions  through  the  fissures,  as  Prof.  Posepny 
(p.  118)  seems  inclined  to  believe. 

In  regard  to  the  contemporaneity  of  the  ore  and  the  rocks, 
and  in  favor  of  a  later  introduction  of  ore  through  fault-fis- 
sures, Prof.  Posepny  (p.  124)  cites  the  influence  of  these  fis- 
sures. In  my  paper,  already  referred  to,  I  have  endeavored  to 
show  how  faults  may  have  influenced  the  deposition  of  ore  with- 
out being  themselves  channels  for  the  flow  of  mineral  solutions, 
and  how  they  may  have  caused  the  contemporaneous  formation 
of  metallic  sulphides  from  sea-water  in  the  body  of  a  forming 
rock ;  the  faulting  fissure  being  formed  at  an  early  period  in 
the  foundation-rocks,  and  probably  continuing  to  be  a  plane  of 
break  and  movement  in  the  deposits  of  later  formation. 

ARTHUR  WINSLOW,  Jefferson  City,  Mo. :  The  results  of  exten- 
sive and  long-continued  studies,  such  as  are  here  presented  by 
Prof.  Posepny,  deserve  most  careful  consideration  before  one 
should  undertake  to  criticise  the  general  conclusions  or  judge  of 
the  broader  bearings  of  his  work.  I  shall  not  attempt  anything 
of  the  kind.  The  remarks  made  by  me  (Trans.,  xxii.,  634, 


THE   GENESIS    OF    ORE-DEPOSITS.  189 

735)  in  the  discussions  of  Mr.  Emmons's  and  Dr.  Jenney's 
papers,  presented  at  this  meeting,  are  to  a  great  extent  applica- 
ble here ;  but  I  wish  to  add  a  few  more  words  bearing  directly 
upon  Prof.  Posepny's  statements  concerning  the  Missouri  and 
Wisconsin  ores. 

On  page  117  he  says  that  while  the  deposits,  away  from  the 
granite  and  porphyry  "  islands  "  of  southeastern  Missouri,  con- 
sist chiefly  of  lead-  and  zinc-ores,  u  other  metals,  such  as  cop- 
per, cobalt  and  nickel,  occur  as  the  Archean  foundation-rocks 
are  approached."  This  circumstance,  he  says,  is  "  an  indica- 
tion that  the  source  of  the  lead-deposits  also  is  to  be  sought  in 
depth."  Whatever  may  be  the  value  of  this  indication,  I  do 
not  think  the  facts  as  stated  hold  generally.  I  judge  that  Prof. 
Posepny  reasons  from  his  observations  at  Mine  La  Motte,  where 
such  conditions  exist.  At  other  points,  however,  these  changes 
in  composition  are  not  observed  as  the  crystalline  rocks  are  ap- 
proached. At  Doe  Run,  a  mine  recently  opened,  work  is  pros- 
ecuted along  the  old  water-worn  pre-Cambrian  surface  of  the 
Archean  granite,  among  the  conglomerate  boulders  them- 
selves ;  and  few  or  no  copper-,  cobalt-  or  nickel-ores  are  found. 
Again  at  other  localities,  in  St.  Genevieve,  Franklin,  Craw- 
ford and  other  counties,  copper-ores  occur  remote  from  any 
granite  or  porphyry  outcrops  and  well  above  the  basal  beds  of 
the  Cambrian. 

With  reference  to  the  Wisconsin  deposits,  our  author  seems 
to  think  the  absence  of  ores,  in  the  great  thicknesses  of  lime- 
stones and  sandstones  which  underlie  the  productive  horizons, 
by  no  means  conclusive  as  an  argument  against  their  deep- 
seated  source,  and  suggests  that  the  solutions  may  have  come 
up  through  a  passage  not  yet  exposed,  and  even  that  fault-fis- 
sures and  eruptive  dikes  may  exist  which  have  not  been  dis- 
covered. From  the  fact  that  he  refers  in  this  connection  only 
to  Whitney's  report  of  1862,  I  conclude  that  he  has  not  had 
access  to  the  later  and  more  exhaustive  works  of  Strong  and 
Chamberlin.  Perhaps  with  the  full  light  conveyed  by  these 
reports  and  accompanying  maps,  Prof.  Posepny  might  have  at- 
tached more  importance  to  the  objections  raised.  For  my  own 
part,  I  do  not  see  how  such  a  passage  for  the  solutions  as  he 
suggests  could  possibly  exist  without  its  presence  having  been 
revealed  and  its  course  traced  through  the  widespread  mining 


190  THE    GENESIS    OF    ORE-DEPOSITS. 

and  exploring  which  has  been  conducted  in  this  region  during 
the  past  seventy  years.  Neither  do  I  yet  see  how  the  solutions 
could  traverse  the  intervening  great  thicknesses  of  water-soaked 
sandstones  without  becoming  diffused,  in  great  part  at  least. 
The  failure  to  find  such  a  passage  and  the  absence  of  the 
ores  in  the  beds  assumed  to  have  been  traversed,  though  evi- 
dence of  a  negative  character,  is  so  strong  that  it  becomes  of 
almost  positive  value  in  support  of  the  theory  of  lateral  segre- 
gation. 

T.  A.  EICKARD,  Denver,.  Colo. :  The  distinguished  author  of 
this  paper  has  referred  to  the  Leadville  monograph  of  Em- 
mons  as  "  epoch-making."  This  judgment  has  been  antici- 
pated, I  believe,  by  most  of  us.  It  serves,  however,  very  well 
to  recall  the  fact  that  the  publication  of  that  particular  mono- 
graph marked  the  high-tide  of  the  lateral-secretion  theory, 
which  owed  its  importance  more  to  the  fact  of  its  acceptance 
by  certain  distinguished  geologists  than  to  its  incomplete  dem- 
onstration by  Sandberger. 

What  Prof.  Posepny  said  of  the  work  of  our  American  geol- 
ogist we  can  say,  with  even  greater  force,  of  his  present  con- 
tribution. His  dissection  of  the  theory  promulgated  by  Sand- 
berger is  most  effective.  The  sympathies  of  the  miner  are 
with  him  in  that  demolition  of  the  lateral-secretion  theory ;  for 
the  latter  was  an  explanation  which  never  found  much  favor 
underground,  with  the  miner,  but  had  its  stronghold  in  its  own 
particular  habitat,  the  professor's  sanctum.  Here  I  would  throw 
out  the  suggestion  to  my  fellow  mining  engineers,  whose  busi- 
ness is  to  observe  rather  than  to  theorize,  that  these  distin- 
guished scientists  must,  after  all,  look  to  the  men  who  spend 
much  time  underground  for  the  accumulation  of  evidence 
whereon  to  found  their  hypotheses.  If  the  genesis  of  ore-de- 
posits is  to  be  unravelled,  more  particularly  if  this  study  is  des- 
tined to  be  capable  of  further  practical  and  economic  applica- 
tion, it  must  be  through  the  gathering  of  facts  and  not  the 
mere  building  of  theories.  Prof.  Posepny  has  very  properly 
pointed  out  that  Sandberger's  views  gained  many  disciples  be- 
cause they  permitted  extensive  generalizations  to  be  made  above 
ground,  and  in  comfort,  but  did  not  so  much  require  a  descent 
underground  and  the  making  of  observations  under  conditions 


THE    GENESIS    OP    ORE-DEPOSITS.  191 

of  discomfort.  Therefore,  I  would  say,  let  those  of  us  who 
have  the  opportunity  aid  in  the  elucidation  of  truth  hy  the  col- 
lection of  the  facts  and  observations  without  which  speculations 
regarding  the  origin  and  formation  of  ore-deposits  are  worse 
than  vain. 

Prof.  Posepny  emphasizes  the  fact  of  the  ascension  of  min- 
eral solutions.  I  venture  to  suggest  that  these  terms — "  ascend- 
ing," "  lateral,"  and  "  descending " — may  all  be  applied  to 
mineral  solutions  at  various  periods  and  under  various  condi- 
tions. It  is  the  great  fact  of  circulation  which  covers  all.  The 
water  which  comes  up  must  have  first  gone  down ;  its  original 
descent  was  as  necessary  to  the  process  of  ore-formation  as  its 
subsequent  ascent.  When  and  where  in  its  journeying  it  be- 
came a  solvent  and  when  and  where  it  became  a  precipitant — 
that  is  what  the  miner  wants  to  know.  The  ultimate  formation 
of  an  ore-deposit  is  dependent  more  upon  conditions  favoring 
precipitation  than  upon  those  determining  solution.*  Prof. 
Posepny  points  out  more  than  once  that  the  two  great  factors 
which  increase  the  solubility  of  all  substances  are  heat  and 
pressure.  We  know  by  observation  that  these  conditions  are 
increasingly  obtainable  as  we  go  downward.  The  deep  region 
is  one  that  favors  solution,  just  as  the  shallow  zone,  because  it 
is  characterized  by  lessened  heat  and  diminished  pressure, 
favors  precipitation.  It  is  this  simple  fact  which  helps  to  ex- 
plain the  ordinary  non-persistence  of  ore  in  depth.  It  is  this 
which  explains  the  comparatively  late  origin  of  ore-deposits. 
The  general  non-persistence  of  ore  in  depth  is  a  fact  capable  of 
proof;  the  comparatively  late  origin  of  most  ore-deposits  is  a 
hypothesis  which  is  founded  upon  observation  and  confirmed 
by  the  consideration  that  the  older  geological  formations  were 
at  some  time  overlaid  by  an  enormous  thickness  of  later  sedi- 
ments, and  therefore  existed  under  conditions  favoring  solution, 
and  not  that  precipitation  to  which  ore-deposition  is  more  di- 
rectly due. 

One  more  point  I  would  wish  to  refer  to.  Prof.  Posepny 
demonstrates  that  at  Przibram  the  metal  of  the  ore-deposits 
could  not  have  come  from  the  eruptive  rock  in  the  immediate 
vicinity  of  the  lodes.  This  is  most  interesting.  For  many  years 

*  Keference  is  intended  particularly  to  the  metals. 


192  THE    GENESIS    OF    ORE-DEPOSITS. 

we  have  been  accustomed  to  references  to  dikes  and  other 
bodies  of  eruptive  rocks  as  being  the  source  of  the  precious 
metals  of  certain  lode-formations.  In  fact,  a  "  dike "  was 
almost  as  necessary  as  a  "  true  fissure-vein,"  a  good  climate, 
plenty  of  timber,  fine  scenery  and  other  factors,  which,  in  a 
prospectus,  are  requisite  to  the  making  of  a  good  mine.  In  my 
Bendigo  paper*  I  have  already  suggested  that  the  vicinity  of 
eruptive  rocks  need  not  necessarily  indicate  that  they  were  the 
source  of  the  metals,  but  that  their  extrusion  afforded  the  heat 
which  made  the  underground  waters  active.  I  would  add  that 
the  contraction,  due  to  cooling,  following  the  extrusion  of  a 
sheet  or  a  mass  of  igneous  rock  may  have  afforded  a  line  of 
least  resistance  or — as  Prof.  Posepny  would  put  it — "  a  line  of 
maximum  circulation." 

In  closing  I  would  express  the  indebtedness  which  we  must 
all  feel  to  Prof.  Posepny  for  so  extensive  and  so  valuable  a  con- 
tribution. In  my  own  case  I  would  express  it  as  the  gratitude 
of  an  apprentice  to  a  master. 

HORACE  Y.  WINCHELL,  Minneapolis,  Minn,  (communication 
to  the  Secretary) :  It  is  an  interesting  fact  that  the  opinions 
here  so  ably  advanced  by  Prof.  Posepny  were  partially  stated  as 
long  ago  as  the  end  of  the  seventeenth  century.  A  few  quo- 
tations from  "  An  Essay  Towards  a  Natural  History  of  the 
Earth,"  by  John  Woodward,  will  make  this  plain.  I  quote 
from  the  third  edition,  published  in  1723,  the  date  of  the  first 
edition  being  1695. 

"That  there  is  a  perpetual  and  incessant  circulation  of  water  in  the  atmos- 
phere ;  it  arising  from  the  globe  in  the  form  of  vapour,  and  falling  down  again  in 
the  form  of  rain,  dew,  hail  and  snow.  That  the  quantity  of  water  thus  rising  and 
falling  is  equal ;  as  much  returning  back,  in  rain,  etc.,  to  the  whole  terraqueous 
globe,  as  was  exhaled  from  its  vapours.  That  tho'  the  quantity  of  water  thus  rising 
and  falling  be  certain  and  constant  as  to  the  whole,  yet  it  varies  in  the  several 
parts  of  the  globe  ;  by  reason  that  the  vapours  float  in  the  atmosphere,  sailing  in 
clouds  from  place  to  place,  and  are  not  restored  down  again  in  a  perpendicular 
upon  the  same  precise  tract  of  land,  or  sea,  or  both  together,  from  which  origi- 
naly  they  arose,  but  any  other  indifferently"  (pp.  132,  133). 

As  to  the  cause  of  the  circulation  of  waters  beneath  the  sur- 
face of  the  earth  he  speaks  as  follows : 

*  Trans.,  xxii.,  289. 


THE    GENESIS    OF    ORE-DEPOSITS.  193 

"  That  there  is  a  nearly  uniform  fire  or  heat  disseminated  throughout  the  body 
of  the  earth,  and  especially  the  interior  parts  of  it ;  the  bottoms  of  the  deeper 
mines  being  very  sultry  and  the  stone  and  ores  there  very  sensibly  hot,  even  in 
winter,  and  the  colder  seasons.  That  'tis  this  heat  which  evaporates  and  elevates 
the  water  of  the  Abyss,  buoying  it  up  indifferently  on  every  side,  and  towards  all 
parts  of  the  surface  of  the  globe  ;  pervading  not  only  the  fissures  and  intervalls  of 
the  strata,  but  the  very  bodyes  of  the  strata  themselves,  permeating  the  interstices 
of  the  sand,  earth  or  other  matter  whereof  they  consist,  yea  even  the  most  firm  and 
dense  marble  and  sandstone.  .  .  .  That  this  vapour  proceeds  up  directly  towards 
the  surface  of  the  globe  on  all  sides,  and  as  near  as  possible,  in  right  lines,  unless 
impeded  and  diverted  by  the  interposition  of  strata  of  marble,  the  denser  sort  of 
stone,  or  other  like  matter,  which  is  so  close  and  compact  that  it  can  admit  it  only 
in  smaller  quantity,  and  this  very  slowly  and  leisurely. 

"That  where  the  vapour  is  thus  intercepted  in  its  passage,  and  cannot  pene- 
trate the  stratum  diametricaly,  some  of  it  glides  along  the  lower  surface  of  it,  per- 
meating the  horizontal  intervall  which  is  betwixt  the  said  dense  stratum  and  that 
which  lies  underneath  it.  The  rest  passes  the  interstices  of  the  mass  of  the  subja- 
cent strata,  whether  they  be  of  laxer  stone,  or  of  marie,  or  the  like,  with  a  direc- 
tion parallel  to  the  site  of  those  strata,  'till  it  arrives  at  their  perpendicular  inter- 
valls" (pp.  136,  137). 

Woodward  entertained  the  idea  that  "  the  whole  terrestrial 
globe  was  taken  all  to  pieces  and  dissolved  at  the  deluge." 

"That  at  length  all  this  metallick  and  mineral  matter,  both  that  which  con- 
tinued asunder,  and  in  single  corpuscles,  and  that  which  was  amassed  and  con- 
creted into  nodules,  subsided  down  to  the  bottom  ;  at  the  same  time  that  did  the 
shells,  teeth,  and  other  like  bodyes  :  as  also  the  sand,  cole,  marie,  and  other 
matter  whereof  the  strata  of  sand-stone,  cole,  marie,  and  the  rest  are  for  the  most 
part  composed  ;  and  so  were  included  in,  and  lodged  amongst,  that  matter.  .  .  . 
And  the  case  of  metalls  and  minerals  being  the  same,  'tis  for  that  reason  that  in 
some  places  we  now  get  iron,  or  vitriol,  but  no  copper  or  alum  :  in  others  we  find 
these,  but  not  those  :  and  in  others  both  these  and  those,  and  perhaps  many  more. 
.  .  .  Thus  we  sometimes  see  whole  strata  compiled  of  metallick  and  mineral 
nodules  :  others  of  pebles,  and  of  flints,  without  the  interposition  of  other  matter. 
.  .  .  Thus  likewise  we  find  strata  consisting  almost  entirely  of  common  salt : 
others  of  ochre  :  and  others  of  several  metalls  and  minerals,  tin,  lead,  vitriol, 
nitre,  and  sulphur  promiscuously,  without  any  considerable  mixture  of  coarser 
terrestrial  matter." 

Of  the  origin  of  veins  he  speaks  in  these  words : 

"  That  the  metallick  and  mineral  matter,  which  is  now  found  in  the  perpendicu- 
lar intervalls  of  the  strata,  was  all  of  it  originaly,  and  at  the  time  of  the  deluge, 
lodged  in  the  bodyes  of  those  strata  ;  being  interspersed  or  scatter' d  in  single 
corpuscles,  amongst  the  sand,  or  other  matter  whereof  the  said  strata  mainly  con- 
sist. That  it  was  educed  thence  and  transmitted  into  these  intervalls,  since  that  time ; 
the  intervalls  themselves  not  existing  till  after  the  strata  were  formed,  and  the 
metallick  and  mineral  matter  was  actualy  lodged  in  them  ;  they  being  only 
breaches  of  the  strata,  and  not  made  till  the  very  conclusion  of  the  catastrophe, 
the  water  thereupon  immediately  withdrawing  again  from  off  the  earth. 


194  THE    GENESIS    OF    ORE-DEPOSITS. 

"That  the  water,  which  ascends  up  out  of  the  Abyss,  on  all  sides  of  the  globe, 
towards  the  surface  of  the  earth,  incessantly  pervading  the  pores  of  the  strata,  I 
mean  the  interstices  of  the  sand  or  other  matter  whereof  they  consist,  detaches 
and  bears  along  with  it  all  such  metallick,  mineral,  and  other  corpuscles  which 
lye  loose  in  its  way,  and  are  withal  so  small  as  to  be  able  to  pass  those  interstices ; 
forcing  them  along  with  it  into  the  perpendicular  intervalls  ;  to  which  it  natur- 
ally directs  its  course,  as  finding  there  a  ready  exit  and  discharge,  being  partly 
exhaled  thence  up  into  the  atmosphere,  and  partly  flowing  forth  upon  the  surface 
of  the  earth,  and  forming  springs  and  rivers. 

"  That  the  water  which  falls  upon  the  surface  of  the  earth  in  rain,  bears  also 
some,  tho'  a  lesser,  share  in  this  action  ;  this,  soaking  into  the  strata  which  lye 
near  the  surface,  straining  through  the  pores  of  them,  and  advancing  on  towards 
their  perpendicular  intervalls,  bears  thither  along  with  it  all  such  moveable  matter 
as  occurs  in  those  pores  in  much  the  same  manner  as  does  the  water  which  arises 
out  of  the  Abyss  with  only  this  difference,  that  this  passes  and  pervades  none  but 
the  superficial  and  uppermost  strata,  whereas  the  other  permeates  also  those  which 
lye  lower  and  deeper.  ( The  vadose  and  deep  underground  circulations  of  Posepny. ) 

11  That  therefore  the  metalls  and  minerals  which  are  lodged  in  the  perpendicu- 
lar intervalls  of  the  strata  do  still  grow  [to  speak  in  the  mineralogists'  phrase], 
or  receive  additional  increase  from  the  corpuscles  which  are  yet  daily  borne  along 
with  the  water  into  them.  Nay  they  have  grown  in  like  manner  ever  since  the 
time  of  the  Deluge,  in  all  such  places  where  those  intervalls  are  not  already  so 
filled  that  they  cannot  receive  any  more  :  or  where  the  stock  of  metallick  and 
mineral  corpuscles,  originally  lodged  in  the  strata,  is  not  quite  exhausted,  and  all 
borne  thither  already.  .  .  . 

"  That  the  metallick  and  mineral  matter  which  lyes  in  the  bodyes  of  the  strata 
does  not  grow,  .  .  .  but  on  the  contrary,  hath  been  diminished  and  lessened 
by  so  much  as  hath  been  conveyed  into  their  perpendicular  intervalls,  and  as 
hath  been  brought  forth  upon  the  surface  of  the  earth  by  springs,  rivers,  and  ex- 
halations from  the  Abyss,  since  that  time.  That  notwithstanding  there  have  and 
do  still  happen,  transitions  and  removes  of  it,  in  the  solid  strata,  from  one  part  of 
the  same  stratum  to  another  part  of  it,  occasion' d  by  the  motion  of  the  vapour 
towards  the  perpendicular  intervalls  of  these  :  and  in  the  laxer  strata,  such  as 
sand,  clay,  and  the  like,  from  the  lower  ones  to  those  which  lye  above  them,  and  even  to 
the  very  surface  of  the  earth  "  (pp.  208-216). 

Although  the  paragraphs  quoted  lead  us  to  infer  that  Wood- 
ward thought  veins  were  filled  by  the  mechanical  transportation 
of  matter  in  small  grains,  yet  there  are  in  other  places  indica- 
tions that  he  also  had  an  idea  of  their  formation  by  the  deposi- 
tion of  minerals  from  solution.  Thus,  nearly  a  century  before 
"Werner  and  Hutton,  were  expressed  ideas  which  were  the  re- 
sults of  long  and  careful  observation  and  study  which,  though 
tinged  with  the  theological  and  so-called  philosophical  doctrines 
of  the  day,  were  yet  true  to  nature  and  of  universal  application, 
and  which  strike  us  as  extremely  valuable  and  original  when 
put  in  modern  logic  and  phraseology. 


THE    GENESIS    OF    ORE-DEPOSITS.  195 

JOHN  A.  CHURCH,  New  York  City  (communication  to  the 
Secretary) :  I  cannot  agree  with  all  the  dicta  of  Prof.  Posepny's 
valuable  paper.  He  says  (page  14,  and  see  page  74)  that 
in  fissures  "  only  the  places  remaining  open  would  permit 
an  active  circulation  of  solutions  and  a  regular  deposition 
from  them."  The  idea  of  deposition  in  a  free  space  runs 
through  the  whole  of  the  paper,  and  is  applied  not  only 
to  the  ore-deposits  of  the  vadose  circulation  but  with  equal 
uniformity  to  those  of  the  deep  circulation.  Such  ideas 
seem  to  me  to  be  incompatible  with  the  crushing  pressure 
which  all  agree  must  be  found  at  depths  of  10,000  and  15,000 
feet.  "We  have  in  metasomatic  replacement  an  explanation 
of  ore-formation  which  accords  so  well  with  the  conditions 
supposable  at  great  depth  that  it  seems  unnecessary  to  add 
to  it  a  requirement  that  is  certainly  contradicted  by  those 
conditions. 

I  believe  I  was  the  first  in  this  country  to  ascribe  the  forma- 
tion of  an  important  vein  (the  Com  stock)  to  metasomatic  altera- 
tion, which  I  then  called  "  substitution,"  the  term  metasomasis 
being  suggested  in  the  same  year.  The  character  of  the  Corn- 
stock  ore  forbids  the  supposition  of  deposition  in  an  open  space ; 
for  it  is  not  quartz  but  a  mixture  of  quartz  and  fragments  of 
the  wall-rock.  In  the  opinion  of  experienced  men  more  than 
half  of  the  rich  ore  mined  from  the  heart  of  the  great  ore-bodies 
was  "  porphyry,"  and  at  least  the  proportion  was  great.  My 
conclusion  was  disputed  by  Mr.  Becker;  but  one  of  the  surest 
advances  which  vein-geology  has  made  in  the  last  fifteen  years 
has  been  the  steady  growth  of  the  idea  that  the  thickest  ore- 
bodies  may  have  been  formed  by  the  replacement  of  masses  of 
wall-rock  fragments,  or  by  the  spread  of  siliceous  replacement 
from  a  narrow  crevice  through  the  walls. 

In  deep-seated  formations  this  method  of  deposition  is  neces- 
sarily supposed ;  for  there  are  not  only  no  open  spaces  there, 
but  the  situation  is  not  even  what  I  conceived  it  to  have  been 
in  the  Comstock.  Nearer  the  surface  there  might  be  partings 
which,  though  minute,  would  be  real  openings,  while  at  great 
depth  such  partings  must  be  so  closely  appressed  as  to  be  no 
more  than  mere  breaks  of  continuity. 

The  tendency  of  opinion  in  this  country  is  toward  metasoma- 
sis acting  upon  masses  of  crushed  rock  in  crevices  which  they 

13 


196  THE    GENESIS    OF    ORE-DEPOSITS. 

completely  fill ;  and  I  find  nothing  in  Prof.  Posepny's  paper 
which  need  cause  a  retreat  from  this  view. 

Prof.  Posepny  appears  to  place  great  reliance  upon  the  ap- 
pearance of  the  ore  and  the  walls  enclosing  it,  and  I  suppose  it 
is  because  deep-seated  deposits  in  limestone  have  some  strong 
resemblances  to  those  of  the  upper  circulation,  that  he  con- 
cludes that  the  former  must  be  laid  down  in  "  spaces  of  disso- 
lution," like  some  of  the  latter.  To  me  these  facts  point  rather 
to  an  identity  of  active  agent  than  to  identical  circumstances  of 
its  action.  To  make  my  meaning  clearer  I  will  recall  some 
well-known  facts  and  theories. 

We  know  that  the  limestone  rocks,  in  proportion  to  their 
amount,  carry  more  ore-bodies  than  the  siliceous  rocks,  though 
the  latter  have  actually  the  greater  number.  The  suitability 
of  limestone  for  the  deposit  of  ores  is  usually  made  to  depend 
upon  its  solubility  in  water  charged  with  carbonic  acid,  which 
is  supposed  to  be  derived  from  the  soil  by  descending  waters. 
It  is  carried  into  the  interior  of  the  earth  and  again  discharged, 
for  the  earth  being  a  closed  vessel  already  full  of  water  into 
which  a  new  supply  is  constantly  poured,  it  is  clear  that  as 
much  must  be  discharged  into  the  atmosphere  by  springs  as  the 
atmosphere  supplies  by  rain.  I  find  fault  with  the  usual  view 
upon  this  subject,  which  apparently  assumes  that  the  deep 
waters  must  be  highly  charged  with  C02  derived  from  the  sur- 
face. On  the  contrary,  it  seems  to  me  that  the  discharging 
water  must  bring  out  as  much  C02  as  it  takes  in,  for  neither 
water  nor  gas  can  be  lessened  in  quantity  except  by  the  com- 
paratively small  amount  that  enters  into  fixed  combinations  in 
the  rocks.  Since  the  solubility  of  gas  in  water  is  increased  by 
pressure  we  must  suppose  that  the  dissolved  C02  remains  with 
the  water  that  absorbed  it  throughout  the  whole  range  of  cir- 
culation and  that  there  cannot  be  any  discharge  of  surface  C02 
in  the  interior.  Yet  we  know  that  large  quantities  of  C02  are 
discharged  from  the  earth  as  gas  not  dissolved  in  water,  besides 
that  which  is  dissolved ;  and  this  gaseous  discharge  must  be  in 
excess  of  the  C02  carried  in.  May  we  not  find  the  source  of 
this  excess  in  deep-seated  metasomatic  replacement  ? 

The  operation  of  solutions  whose  composition  we  do  not 
know  can  be  judged  only  by  their  effects.  When  metasomatic 
replacement  takes  place  in  limestone  it  is  generally  assumed 


THE    GENESIS    OF    ORE-DEPOSITS.  197 

that  lime  carbonate  goes  into  solution,  while  its  place  is  taken 
by  the  ore-substances,  that  is  to  say,  that  the  action  is  molecu- 
lar substitution  and  not  atomic ;  but  it  is  conceivable  that  the 
change  should  begin  by  an  interchange  of  acidic  elements — 
that  Si02  should  drive  out  C02.  Subsequent  changes  might 
remove  the  lime  silicate  by  another  process  of  substitution, 
since  it  is  more  soluble  than  silica ;  but  the  point  is  that  C02 
would  be  liberated,  and  though  the  original  ore-solution  were 
free  from  C02,  it  would  immediately  become  charged  with  that 
agent  and  exert  the  well-known  dissolving  power  of  carbonic 
acid  solutions.  In  this  way  a  solution  which  would  have  but 
feeble  power  in  other  rocks  may  in  limestone  set  up  a  chain  of 
reactions  that  would  intensify  its  effects.  These  considerations 
lead  to  interesting  conclusions. 

We  have  a  source  of  C02  in  rocks,  however  deep-seated,  and 
consequently  effects  may  be  produced  at  any  depth,  which 
simulate  those  of  surface-waters,  though  probably  without  the 
production  of  caverns.  Since  the  mode  of  solution  is  the  same, 
the  appearance  of  the  walls  lining  an  ore-body  and  the  appear- 
ance of  the  ore  itself  may  be  almost  precisely  the  same  as  in 
the  vadose  region. 

Limestone  contains  the  elements  for  self-destruction,  since 
the  breaking  up  of  one  lime-carbonate  molecule  may  cause  the 
solution  of  another ;  and,  as  this  cannot  be  said  of  any  other 
rock,  we  reach  a  possible  explanation  of  the  comparative  fre- 
quency of  ore-bodies  in  limestone.  The  dolomites  would,  of 
course,  present  similar  reactions. 

There  are  two  questions  which  are  distinguished,  even  in  the 
difficult  study  of  veins,  by  the  obscurity  which  hangs  over 
them.  One  is  the  selection  of  a  favored  stratum  for  ore-depo- 
sition. In  some  situations  the  solutions,  before  reaching  the 
stratum  of  actual  ore-deposition,  must  have  passed  several 
strata  suitable  for  their  action,  if  they  had  possessed  from  the 
beginning  the  power  of  solution  which  they  showed  ultimately. 
I  believe  this  objection  has  been  urged  against  the  lateral-secre- 
tion theory  as  applied  to  Leadville.  Ore-solutions  exhibit  a 
selective  power  which  is  extraordinary  in  a  water  fully  supplied 
with  dissolving  qualities,  but  quite  explicable  in  a  solution 
which  lacks  this  power.  I  suppose  it  is  impossible  at  present 
to  determine  why  the  rocks  now  exposed  at  Leadville  were 


198  THE    GENESIS    OF    OKE-DEPOSITS. 

selected  for  attack  by  the  solutions ;  but  I  think  it  is  compre- 
hensible why  that  action,  however  extensive,  should  be  localized 
by  the  development  and  action  of  C02  in  the  neighborhood 
where  it  began. 

An  obvious  consequence  of  these  considerations  is  that  the 
aqueous  circulation  of  the  earth  becomes,  through  the  medium 
of  metasomasis,  a  means  for  restoring  to  the  atmosphere  accu- 
mulations of  carbon  that  represent  the  organic  life  of  past 
times. 

The  second  obscure  question  is  logically  one  which  ought  to 
be  answered  before  we  discuss  the  origin  of  ore  at  all.  It  is  the 
secondary  alteration  of  already-formed  ore-deposits.  I  have 
no  doubt  that  some  of  the  deep-seated  deposits  which  we  see 
are  actually  a  product  of  the  vadose  circulation.  Formed  ten 
thousand  feet  below,  they  have  been  raised  until  they  are  now 
ten  thousand  feet  above  the  sea-level,  and,  during  the  immense 
period  through  which  they  have  been  subjected  to  the  surface 
circulation,  they  have  not  only  been  re-arranged  but  may  have 
actually  lost  their  ancient  origin.  Even  the  rock  in  which  they 
were  deposited  may  have  been  removed  and  the  ore  transferred 
to  another  member  of  the  series.  Structural  facts  may  prove 
deep-seated  deposition,  but  actually  the  ore-bodies  we  see  are 
often  in  whole  or  in  part  hysteromorphs.  This  is  especially 
true  in  limestone  deposits.  Though  these  facts  are  well-known, 
they  do  not  exert  the  controlling  influence  upon  opinion  which 
I  think  they  deserve,  probably  because  of  the  extreme  difficulty 
of  separating  the  primary  from  the  secondary  phenomena.  No 
writer  that  I  have  seen  has  given  to  this  subject  half  the  im- 
portance which  a  mining  engineer  must  give  it. 

I  cannot  agree  with  the  author  in  giving  so  much  importance 
to  crustificatiori,  as  he  describes  it.  Certainly  a  banded  struc- 
ture can  arise  from  the  replacement  of  fragments  arranged  in 
layers  by  pressure  and  friction,  as  well  as  in  many  other  ways, 
arid  does  not  prove  deposition  in  a  cavity,  whether  filled  by 
water  or  air.  He  has  misunderstood  me  in  saying  that  I  found 
crusts  of  quartz  alternating  with  calcite  in  the  Justice  mine 
(Comstock).  I  said  the  thick  masses-  of  calcite  in  that  mine 
rested  on  a  thin  layer — an  inch  or  two — of  quartz ;  but  this  is 
not  crustification  in  the  author's  sense.  My  view  of  that  oc- 
currence was  that  an  insignificant  quartz  seam,  probably  be- 


THE    GENESIS    OF    ORE-DEPOSITS.  199 

longing  to  the  last  period  of  the  Comstock,  was  first  produced, 
and  that  the  calcite  was  formed  by  replacement  of  the  wall-rock 
at  a  later  period.  There  is  not  the  least  evidence  of  deposition 
in  a  cavity.  If  there  is  crustification,  that  appearance  does  not 
have  the  significance  which  our  author  gives  to  it. 

I  have  not  attempted  to  particularize  the  many  points  in 
which  I  find  myself  in  agreement  with  the  author;  and  since 
my  remarks  have  been  rather  in  criticism,  I  desire  to  express, 
in  conclusion,  my  high  appreciation  of  his  admirable  treatise. 

S.  F.  EivynoNS,  Washington,  D.  C.  (communication  to  the 
Secretary) :  Prof.  Posepny's  paper,  or  treatise,  as  it  rather  de- 
serves to  be  called,  is  a  most  important  contribution  to  the  theory 
of  ore-deposits.  His  wide  personal  observation  of  most  of  the 
important  mines  in  so  many  different  parts  of  the  world  and 
his  critical  acumen  as  an  observer,  combined  with  his  long-con- 
tinued studies  of  the  subject,  give  to  his  words  an  exceptional 
authority.  Whatever  might  be  said,  therefore,  in  praise  of  his 
article  (and  it  would  take  much  time  to  say  it  all)  would  hardly 
add  to  its  value.  But  the  very  high  quality  of  his  work  ren- 
ders any  errors  in  it  exceptionally  hurtful,  and  I  shall  therefore 
confine  my  remarks  mainly  to  what  seem  to  me  to  be  erroneous 
teachings,  and  to  points  in  which  I  differ  with  him  either 
wholly  or  in  part.  I  would  first  say,  however,  that  to  the 
greater  part  of  the  views  put  forth  in  this  paper  I  most  heartily 
subscribe,  especially  to  those  on  underground  circulation,  and 
on  the  great  rarity  of  ore-deposits  which  have  been  formed 
contemporaneously  with  the  enclosing  rocks. 

It  is  well  known  that  for  some  years  past  there  has  been  a 
very  warm  discussion  between  Posepny  and  Stelzner  on  the  one 
side,  and  Sandberger  on  the  other,  in  regard  to  the  derivation 
of  the  material  of  ore-deposits,  the  former  holding  to  the  as- 
cension, the  latter  to  the  lateral-secretion  theory.  Without  at- 
tempting to  determine  the  merits  of  either  side  of  the  contro- 
versy, which  it  would  be  unwise  to  do  without  examining 
personally  the  deposits  in  question  and  their  geological  sur- 
rounding, one  is  inclined  to  believe  that  the  views  of  either  of 
such  able  geologists  must  have  scientific  value,  whether  one  or 
the  other  may  be  proved  to  be  erroneous  in  a  particular  in- 
stance. I  regret,  however,  to  see  this  controversy  brought  into 


200  THE    GENESIS    OF    ORE-DEPOSITS. 

what  should  be  a  broad  and  impartial  discussion  of  the  facts  of 
nature,  and  to  detect  in  certain  cases  what  appears  to  be  a  ten- 
dency on  the  part  of  Prof.  Posepny  to  adopt  a  rather  forced 
construction  of  these  facts,  in  order  to  make  them  support  his 
views  rather  than  those  of  Sandberger. 

The  lateral-secretion  theory,  which  Posepny  ascribes  to  Sand- 
berger, is  much  narrower  than  that  which  I,  and  I  think  most 
American  geologists,  hold.  It  confines  the  derivation  of  the 
vein-contents  to  the  wall-rock  in  immediate  contact  with  the 
deposit ;  whereas,  in  my  view,  a  derivation  from  rocks  within 
reasonable  proximity,  as  opposed  to  a  source  -at  unknown 
depths  ("  in  the  bary sphere  "),  would  constitute  lateral-secre- 
tion, and  ore-bearing  currents  may  in  such  cases  have  had  an 
upward,  downward  or  lateral  motion,  according  to  differing 
local  conditions  of  rock-structure.  Prof.  Posepny  himself  ad- 
mits, in  his  admirable  discussion  of  vadose  or  shallow  and 
deep  underground  circulation,  the  possibilities  of  such  lateral- 
secretion  when  he  describes  the  latter  (p.  28)  in  the  follow- 
ing words : 

"  The  ground- water  descends  in  the  deep  regions  also  through  the  capillaries 
of  the  rocks ;  at  a  certain  depth  it  probably  moves  laterally  towards  open  con- 
duits, and  reaching  these,  it  ascends  through  them  to  the  surface." 

The  distinction  between  the  action  of  surface  and  that  of 
deep-seated  waters  is  an  important  one  in  the  study  of  ore- 
deposition;  but  I  do  not  think  that  Prof.  Posepny  is  justified 
in  assuming,  as  he  does,  that  only  ascending  waters  are  capable 
of  depositing  ores.  Furthermore,  the  necessary  derivation  of 
metallic  minerals  by  these  ascending  waters  from  the  "  bary- 
sphere  "  seems  too  far-fetched.  At  what  depth  the  barysphere 
will  be  found,  meaning  thereby  the  part  of  the  earth's  interior 
where  the  rocks  have  a  much  higher  specific  gravity  than  those 
that  come  under  our  observation,  is  purely  a  speculative  ques- 
tion ;  but  as  our  surface  observations  extend  over  a  thickness  in 
round  numbers  of  about  100,000  feet  of  rocks,  and  show  no 
appreciable  difference  of  specific  gravity  between  the  deeper 
and  more  shallow  rocks,  except  such  as  is  due  rather  to  differ- 
ent degrees  of  density  than  to  heavier  mineral  constituents,  it 
seems  safe  to  assume  that  such  a  barysphere  must  exist,  if  at 
all,  at  such  great  depths  as  to  be  beyond  the  reach  of  any  min- 


THE    GENESIS    OF    ORE-DEPOSITS.  201 

eral-bearing  waters.  If  such  a  zone  rich  in  heavy  metals  exists 
in  depth,  as  there  is  some  reason  to  believe,  my  own  view,  as 
expressed  in  my  paper  read  at  this  meeting,  is  that  the  heavy 
metals  which  constitute  the  ore-deposits  were  brought  up  from 
it  into  the  outer  crust  of  the  earth  by  the  various  eruptive 
rocks,  and  were  partially  concentrated  in  certain  parts  of  these 
eruptive  rocks  by  differentiation  during  the  process  of  cooling. 
In  this  view  I  agree  with  Vogt,  whom  Prof.  Posepny  men- 
tions (p.  147)  in  a  somewhat  slighting  manner.  I  differ 
with  Vogt,  however,  in  that  I  consider  the  greater  part  of 
our  ore-deposits,  all  certainly  that  have  come  under  my  limited 
observation,  to  be  due  to  further  concentration,  perhaps  many 
times  repeated,,  both  chemical  and  mechanical ;  and  I  am  en- 
tirely at  one  with  Prof.  Posepny  in  considering  their  final  con- 
centration into  their  present  form  to  be  due  to  the  action  of 
circulating  waters. 

Prof.  Posepny's  belief  in  the  capabilities  of  an  ascending  cur- 
rent of  heated  waters  or  thermal  springs  seems  to  me,  in  some 
instances,  as  exaggerated  and  unreasonable  as  his  rendering 
makes  Sandberger's  disbelief,  in  the  instances  he  cites.  He 
quotes  a  single  observation  by  Noggerath  in  1845  on  the  find- 
ing of  vertical  channels  in  limestone  8  to  35  inches  in  diameter, 
near  Aachen,  which  are  supposed  to  have  been  eaten  out  by 
the  ascending  spring-waters,  and  from  this  draws  the  wide- 
reaching  conclusion  that  ascending  waters  may  actually  force 
their  way  up  through  rock  masses  without  the  necessity  of  pre- 
existing cracks  or  channels.  Among  instances  where  he  uses 
this  explanation  to  account  for  the  formation  of  an  ore-deposit 
the  most  remarkable  is  that  of  Laurium  (p.  135),  where  the 
ore-deposits  as  shown  by  the  diagrammatic  section  (Fig.  87) 
are  funnel-shaped  bodies  extending  outward  from  the  contact 
of  flat-lying  schists  into  subjacent  and  superjacent  limestones, 
that  is  both  upwards  and  downwards.  My  own  explanation  of 
this  section,  deduced  by  observations  in  limestone-deposits  in 
this  country,  would  be  that  the  ore-bearing  currents  circulating 
along  the  contact-planes  had  eaten  outward  into  the  more  solu- 
ble rock,  upwards  from  the  upper  contact,  and  downwards  from 
the  lower  contact.  But  Prof.  Posepny  explains  the  funnel-shape 
of  the  ore-bodies  on  the  upper  contact  as  produced  "  by  the 
pressure  of  the  ascending  solutions.0  The  lower  contact  he 


202  THE    GENESIS    OF    ORE-DEPOSITS. 

offers  no  explanation  for,  but  says  "  it  is  perhaps  somewhat 
ideally  sketched." 

It  is  unprofitable,  however,  to  discuss  deposits  which  neither 
of  us  have  seen ;  for  nothing  is  so  liable  to  misconception  as 
the  description  of  ore-deposits  one  has  not  seen  by  a  person 
w;ith  whose  qualifications  and  accuracy  of  observations  one  is 
not  familiar.  This  is  shown  in  Prof.  Posepny's  remarks  upon 
the  Leadville  deposits,  in  which  he  concludes  that  I  must  ac- 
knowledge that  my  views  in  regard  to  the  downward  course  of 
the  ore-bearing  solutions  were  incorrect,  because  several  mining 
engineers  have  shown  them  to  be  untenable.  It  does  not  seem 
to  occur  to  him  that  the  views  of  a  mining  engineer  (who  is 
not  necessarily  a  geologist)  based  upon  studies  of  a  single  mine 
or  set  of  mines  would  be  of  less  value  as  applied  to  such  theo- 
retical questions  than  those  of  a  trained  geologist  who  had 
made  a  study  of  all  the  geological  conditions  and  mines  of  a 
district.  Of  the  three  articles  quoted  by  him,  that  of  Mr. 
Freeland  offers  no  opinion  upon  the  subject  in  question.  Both 
this  and  Mr.  Rolker's  article  were  written  before  my  mono- 
graph was  published,  otherwise  Mr.  Rolker  would  have  found 
his  objections  on  these  points  foreseen  and  accounted  for  there 
(p.  490). 

In  the  summer  of  1890  I  spent  nearly  two  months  at  Lead- 
ville studying  the  recent  developments  with  the  special  purpose 
of  testing  the  correctness  of  my  former  deductions,  and  Mr. 
Blow  accompanied  me  through  the  workings  of  North  Iron 
Hill,  with  which  he  is  so  familiar.  While  I  naturally  found 
many  details  of  geological  structure  which  were  not,  and  could 
not  have  been,  correctly  represented  on  the  underground  sec- 
tions accompanying  my  report,  I  found  no  reason  to  change  my 
views  of  the  manner  of  formation  of  the  ore-deposits,  and  I  con- 
vinced myself  (and  I  think  Mr.  Blow  also)  that  his  objections 
were  based  on  a  misapprehension  of  certain  geological  phe- 
nomena. It  were  too  long  to  give  here  all  the  results  of  my 
observations,  which  I  regret  that  circumstances  beyond  my 
control  have  as  yet  prevented  me  from  publishing.  I  will  say, 
however,  as  bearing  upon  this  point,  that  in  no  case  did  I  find 
any  convincing  evidence  of  the  action  of  ascending  solutions. 
The  ore-bodies  occur  in  two  general  forms,  either  on  the  ap- 
proximately horizontal  contact-planes  of  porphyry  and  lime- 


THE    GENESIS    OF    ORE-DEPOSITS.  203 

stone,  or  along  nearly  vertical  fissures  crossing  the  limestone 
beds.  In  either  case,  wherever  the  form  of  the  ore-hody  was 
such  as  to  throw  any  light  upon  the  probable  direction  of  the 
ore-forming  currents,  it  showed  that  they  must  have  descended, 
for  they  all  terminated  more  or  less  in  a  point  or  wedged  out 
downwards. 

Before  discussing  this  further,  it  may  be  well  to  repeat  my 
statement  given  in  the  monograph  (p.  379)  which  has  evidently 
been  overlooked  or  misapprehended  by  my  critics.  I  say,  with 
regard  to  the  immediate  source  of  the  ores  : 

"  1.  That  they  came  from  above.  2.  That  they  were  derived  mainly  from  the 
neighboring  eruptive  rocks. 

"By  these  statements  it  is  not  intended  to  deny  the  possibility  that  the  mate- 
rials may  originally  have  come  from  great  depths,  nor  to  maintain  that  they  were 
necessarily  derived  entirely  from  eruptive  rocks  at  present  immediately  in  con- 
tact with  the  deposits." 

I  do  not  maintain,  as  many  have  assumed,  that  the  ore  was 
derived  from  the  white  porphyry.  I  do  not  pretend  to  be  able 
to  determine  what  particular  body  of  porphyry  it  came  from. 
The  objection  of  Mr.  Blow  that  it  could  not  have  come  from  the 
white  porphyry  because  this  is  not  all  decomposed  (not  "  not  at 
all  decomposed,"  as  Prof.  Posepny  puts  it),  is  based  upon  a  mis- 
apprehension of  what  constitutes  decomposition.  If  Prof. 
Posepny  will  read  the  description  of  the  eruptive  rocks  in  my 
chapter  on  rock-formations,  he  will  see  that  all  the  Leadville 
porphyries  are  more  or  less  decomposed  within  this  district; 
when  Mr.  Cross  and  I  were  making  our  geological  studies  we 
had  to  go  several  miles  away  before  we  could  find  a  specimen 
of  unaltered  white  porphyry  for  microscopical  study. 

My  contention  with  regard  to  the  ores  of  this  district,  as 
opposed  to  the  theoretical  views  of  Prof.  Posepny  and  those  of 
his  school,  would  not  have  been  essentially  affected,  however, 
if  it  had  been  shown  that  the  solutions  had  ascended  to  reach 
the  locus  of  the  present  deposits.  The  fissures  across  the  lime- 
stone which  gave  access  to  the  solutions  forming  the  ore-shoots 
of  North  Iron  Hill  described  by  Mr.  Blow  are,  as  I  showed  in 
my  monograph,  faults  with  only  a  few  feet  of  displacement,  and 
can  extend  to  only  limited  depth ;  in  some  cases  their  lower 
limit  could  be  detected.  The  great  faults  which  extend  several 
thousand  feet  in  depth  are  not  ore-bearing,  except  in  so  far  as 


204  THE   GENESIS    OF    ORE-DEPOSITS. 

ore  has  been  dragged  into  them  in  the  movement  of  their 
walls,  one  upon  the  other.  But  the  extent  in  depth,  even  of 
these  great  faults,  must  be  extremely  limited  as  compared  with 
the  distance  of  the  barysphere.  I  believe  that  the  eruptive 
rocks  originally  brought  up  the  heavy  metals  from  the  depths 
into  the  general  region  in  which  the  ores  are  now  found.  Some 
of  these  eruptives  still  contain  over  four  per  cent,  of  them,  in 
spite  of  all  the  leaching  to  which  they  have  been  exposed. 
The  ore-deposits  are  concentrations  of  these  materials  by  deep 
underground  waters,  flowing  along  natural  channels,  and  de- 
positing along  those  which  admitted  a  comparatively  free  flow, 
as  compared  with  a  capillary  circulation.  Such  a  flow  may 
have  been  upward,  downward  or  lateral,  according  to  varying 
structural  conditions.  The  ascending  solutions  which  Prof. 
Posepny  contemplates,  however,  could  not  have  formed  ore- 
bodies  of  the  form  of  those  found  in  Leadville ;  and  it  was  for 
that  reason  that  I  laid  stress  upon  the  evidence  of  their  proba- 
ble downward  course. 

As  regards  the  phenomena  of  "  crustification,"  I  may  not 
have  been  explicit  enough  in  stating  its  absence.  In  my  origi- 
nal examination  I  searched  in  vain  for  any  evidence  of  it.  In 
my  second  examination,  almost  entirely  in  bodies  of  unaltered 
sulphides,  I  found  overwhelming  evidence  that  the  ore  was  not 
deposited  in  pre-existing  cavities,  but  by  metasomatic  replace- 
ment of  the  limestone.  In  the  great  bodies  of  the  A.  Y., 
Minnie  and  adjoining  mines  not  only  could  every  detail  of  the 
granular  structure,  joints  and  cleavage  of  the  original  lime- 
stone be  detected  at  times  in  the  sulphide  ore,  but  even  the 
cracks  in  the  top  of  the  ore-body  through  which  the  ore-bear- 
ing solutions  had  descended  were  often  visible.  In  abandoned 
drifts,  where  the  limestone  dust  had  accumulated  on  the  walls, 
one  would  have  supposed  the  walls  to  be  all  limestone  until  the 
breaking  oif  of  a  fresh  fragment  by  the  hammer  showed  the 
metallic  gleam  beneath. 

G.  F.  BECKER,  Washington,  D.  C.  (communication  to  the 
President  from  Newport,  R.  I.) :  The  paper  of  Prof.  Posepny 
is  a  very  valuable  contribution  to  the  science  of  ore-deposits, 
and  deserves  a  more  careful  critical  discussion  than  I  am  able 
to  assist  in  giving  to  it  at  this  time/ in  the  absence  of  facilities 


THE    GENESIS    OF    ORE-DEPOSITS.  205 

for  reference  to  authorities,  etc.  A  few  general  observations, 
therefore,  must  suffice  at  present  to  indicate  my  views. 

The  theory  of  the  substitution  of  ore  for  rock  is  to  be  ac- 
cepted only  when  there  is  definite  evidence  of  pseudomorphic, 
molecular  replacement.  Prof.  Posepny  is  very  clear  on  this 
point  (p.  13),  and  I  have  insisted  upon  it  in  my  memoir  on 
quicksilver-deposits  and  in  a  paper  on  quicksilver  about  to  be 
distributed.  Prof.  Posepny  appears  to  me,  on  the  other  hand, 
to  lay  too  much  weight  upon  the  structure  which  he  calls 
"  crustification,"  as  indicating  exclusively  the  filling  of  open 
cavities  and  the  absence  of  replacement.  Metamorphic  pro- 
cesses are  very  frequently  accompanied  by  the  formation  of 
layers  similar  to  stratification  and  crustification,  and,  indeed, 
from  similar  causes.  Strata  are  distinguishable  only  because 
the  circumstances  of  deposition  undergo  more  or  less  marked 
variations,  and  the  banded  structure  of  agate  or  hematite  is 
also  due  to  variations  in  conditions  of  deposition  such  as  the 
strength  of  the  solutions,  or  the  rapidity  of  their  flow,  or  tem- 
porary changes  in  the  composition  of  the  fluid.  It  appears  to 
me  that  the  banded  structure  attending  metamorphism,  as  a 
matter  of  observation  in  many  cases,  is  due  to  entirely  similar 
causes.  Thus  a  mass  of  iron  immersed  in  a  copper-solution 
will  precipitate  the  copper  as  a  laminated  mass,  unless  great 
precautions  are  taken  to  secure  uniformity  of  temperature,  etc. 
In  short,  lamination  is  an  ordinary  attendant  of  processes  of 
deposition,  whether  by  replacement  or  otherwise,  whenever 
they  are  so  slow  as  to  be  subject  to  changes  of  condition. 
Hence  crustification  seems  to  me  an  insufficient  guide  to  genetic 
diagnosis. 

The  indications  of  replacement  which  I  should  rely  upon  are 
twofold  :  crystalline  pseudomorphosis  and  the  irregular  enlarge- 
ment of  fissures  in  the  replaced  mass.  Of  the  latter,  Prof. 
Posepny  gives  a  good  illustration  (Fig.  85).  As  for  pseudo- 
morphosis, it  has  a  very  important  bearing  on  the  work  of  Mr. 
Emmons  and  of  J.  S.  Curtis,  for  it  appears  to  be  thoroughly  well 
established  that  galena  forms  pseudomorphs  after  calcite  ;  and, 
therefore,  the  theory  of  replacement  of  limestone  which  they 
advocate  is,  to  say  the  least,  possible.  The  studies  of  these  ob- 
servers at  Leadville  and  Eureka  tend  to  show  that  replacement 
has  been  the  chief  process ;  but  so  far  as  I  can  recall  their  re- 


206  THE    GENESIS    OF    ORE-DEPOSITS. 

marks  they  do  not  assert  the  entire  absence  of  deposition  in 
pre-existing  openings;  so  that  even  if  crustification  were  an  in- 
fallible sign  of  filling,  the  detection  of  crusts  (Posepny,  p.  114) 
would  not  invalidate  their  position.  Another  objection  to  Mr. 
Emmons's  views  is  expressed  by  Prof.  Posepny  in  the  sentence 
(p.  109),  "  It  is  difficult  to  believe  that  metasomatic  processes 
could  produce  such  pronounced  ore-shoots  as  those  described  at 
Leadville."  I  cannot  share  this  view,  for  replacement,  like  so- 
lution, must  occur  along  fissures  or  channels,  and  metasomatic 
ore-bodies  will  present  analogies  in  form  to  the  open  spaces  of 
caves  of  solution. 

It  seems  substantially  certain  that  open  cavities  in  limestones 
can  form  only  above  the  permanent  water-level  of  a  country, 
since  in  such  a  country  the  water  below  this  level  must  be  ap- 
proximately saturated  with  calcium  carbonate.  On  the  other 
hand,  replacement  may  take  place  at  any  depth.  Now,  in  the 
Great  Basin,  the  Tertiary  and  Early  Quaternary  were  very  wet 
periods,  and  if  the  Eureka  limestones  have  been  excavated  by 
surface  waters,  the  excavation  and  subsequent  ore-deposition, 
according  to  Prof.  Posepny's  view,  must  be  crowded  into  the 
late  Quaternary.  The  present  precipitation  of  that  region 
would  seem  insufficient  to  bring  about  much  cave-formation, 
while  a  greater  precipitation  would  raise  the  water-level.  Thus, 
so  far  as  Eureka  goes,  the  hypothesis  of  subsequent  filling 
raises  distinct,  though  perhaps  not  insuperable,  difficulties  as  to 
the  formation  of  the  cavities. 

The  foregoing  notes  should  be  reinforced  by  examples  and 
citations  which  I  cannot  now  furnish. 

F.  M.  F.  CAZIN,  Hoboken,  N".  J. :  If  I  venture  to  add  a  few 
lines  to  Prof.  F.  Posepny's  treatise  on  the  genesis  of  ore-de- 
posits, my  justification  is  derived  from  practical  work  done  and 
consequent  opportunities  enjoyed  in  a  region  to  which  the 
learned  author  personally  has  remained  a  stranger,  and  of 
which  in  existing  literature  no  such  account  is  available  as 
would  afford  to  him  the  powerful  argument  in  favor  of  his  the- 
ories really  presented  by  the  region  itself,  to  a  degree  of  im- 
portance beyond  any  other  mentioned  by  him. 

The  region  to  which  I  refer  furnishes  a  demonstration  of  the 
xenogenous  origin  of  ore-deposits,  heretofore  considered  as 


THE    GENESIS    OF    OEE-DEPOSITS.  207 

idiogenous,  which  I  may  properly  call  gigantic,  and  which  is 
equalled  nowhere  on  the  face  of  the  earth  as  far  as  known.  I 
refer  to  the  region  so  tersely  described  by  James  Douglas 
(Trans.,  xix.,  694)  in  these  words: 

"In  the  Appalachian  chain  from  Vermont  to  Georgia  there 
are  imbedded  in  the  crystalline  schists  large  masses  of  pyrites, 
some  consisting  of  ordinary  bisulphide  of  iron  but  most  of  them 
of  pyrrhotite,  and  all  carrying  more  or  less  copper." 

There  is,  on  the  long  stretch  from  Vermont  (Mr.  Douglas 
might  have  truly  said  "  from  Canada  and  Maine  ")  to  Georgia, 
no  older  mine,  and  none  with  more  important  development  on 
the  ore-deposits  thus  described,  than  that  which  has  been  called 
by  State-legislative  act  "  the  Vermont  Copper  Mine."  Its  his- 
tory began  before  the  world  knew  about  copper  on  the  shore 
of  Lake  Superior.  For  many  years  it  produced  at  the  rate  of 
3,500,000  pounds  of  copper  per  annum,  and,  with  adequate  im- 
provements, could  do  so  to-day.  I  have  seen  its  developments 
on  a  deposit  dipping  24°  KE.  to  a  distance  of  2350  feet  from 
the  surface,  and  to  a  vertical  depth  below  sea-level  of  several 
hundred  feet,  the  lateral  expansion  of -slopes  ranging  between 
50  and  350  feet.  Having  been  connected  with  this  mine  from 
early  in  1882  to  June  of  1888, 1  have  had  opportunity  to  search 
for  the  origin  of  the  ore-body  there  exploited. 

Having  discovered  unmistakable  local  evidence  as  to  the  true 
nature  of  such  origin,  it  remained  to  ascertain  the  identity  or 
uniformity  of  effect  from  identical  causes  or  other  deposits  fall- 
ing under  the  description  above  quoted ;  and  it  was  not  diffi- 
cult to  establish  such  identity  and  harmony. 

At  a  distance  of  ten  miles  in  a  northerly  direction  another 
mine  in  the  same  geological  position,  at  Corinth,  offered  evi- 
dence leading  to  the  same  conclusions,  and  in  a  southern  direc- 
tion at  a  distance  of  four  miles,  the  Straffbrd  mines,  and  at  a 
further  distance  of  sixteen  miles  the  Pompanoosuc  mine,  all 
similarly  situated,  demonstrated  the  same  effects  under  similar 
causes.  And  a  visit  to  many  other  localities  within  the  Hu- 
ronian  Appalachian  region  could  confirm  only  the  conclusions 
to  which  the  observations  in  the  Vermont  mine  had  been  lead- 
ing me. 

Except  as  to  dip,  topography  and  shape  of  workings,  Fig.  56 
in  Prof.  Posepny's  paper  might  well  serve  as  the  image  of  the 


208  THE    GENESIS    OF    ORE-DEPOSITS. 

Vermont  ore-deposit,  represented  on  a  vertical  plane  along  its 
dip.  And  Figs.  54  and  55  may  well  serve  as  a  representation 
of  horizontal  and  vertical  planes,  as  they  are  seen  inside  and 
outside  of  the  Vermont,  Corinth  and  Strafford  mines,  where 
the  designs  shown  in  these  figures  not  only  occur  in  dimensions 
varying  from  a  few  fathoms  to  many  hundreds  of  fathoms,  but 
also  in  varying  material.  In  the  mine,  this  consists  of  the  sul- 
phides of  iron  and  copper,  and  outside  and  at  distant  points 
therefrom,  in  an  admixture  of  carbon-matter  (graphite)  in  the 
country-rock.  This  rock  is  a  micaceous  schist,  the  graphitic 
part  varying  in  proportion  from  a  mere  trace  to  100  per  cent., 
becoming  marketable  plumbago  in  many  localities,  though  with- 
out sufficient  extent,  as  a  rule,  for  exploitation. 

But  it  is  not  on  the  similarity  of  design  between  sulphide  and 
carbon  admixtures  in  the  rock  alone  that  my  conclusions  were 
built,  as  a  description  of  the  mine  will  further  show. 

In  their  lateral  expansion  the  ore-stopes  in  the  Vermont  mine 
present  a  figure  very  similar  to  the  one  presented  in  Prof.  Po- 
sepny's  Fig.  93,  if  the  longitudinal  extent  be  assumed  as  2350 
feet,  with  the  lower  part  broadened.  But  similar  figurations 
are  also  presented  on  a  smaller  scale,  where  in  quarries  the  rock 
is  laid  bare  on  one  of  its  dark  seams. 

The  roof  and  floor  of  the  Vermont  ore-deposits  are  virtually 
impenetrable  to  water;  the  mine  at  1000  feet  vertical  depth 
being  dry.  But  there  is  uncovered  at  a  distance  of  a  few  hun- 
dred feet  from  the  outcrop  an  almost  vertical  cross-fissure  or 
fault  (without  perceptible  faulting),  filled  with  calcareous  spar 
containing  sparsely  distributed  small  seams  of  galena,  which 
cross-fissure  allows  a  few  hundred  gallons  of  water  a  day  to 
percolate  into  the  workings.  Some  of  this  water  finds  its  exit 
through  an  abandoned  adit.  Where  it  reaches  the  surface, 
and  where  its  flow  is  slow,  allowing  evaporation,  it  deposits  a 
slime  of  virgin-white  carbonate  of  lime ;  and  as  it  passes  down 
into  the  valley,  it  deposits  for  miles  a  mixture  of  carbonates 
of  lime  and  iron,  giving  to  the  creek-beds  their  peculiar  coat- 
ing of  color,  as  a  result  of  atmospheric  reduction  of  the  iron 
carbonate. 

The  ore  of  the  Vermont  in  its  mineral  character  has  one 
main  peculiarity,  which  is  common  to  the  deposits  as  described 
from  Canada  to  Virginia  and  Georgia,  namely,  that  quantita- 


THE    GENESIS    OF    ORE-DEPOSITS.  209 

tive  analysis  shows  neither  the  figures  required  to  constitute 
the  one  of  its  components  as  ferro-sulphide,  nor  those  required 
to  show  it  as  ferri-sulphide,  these  figures  varying  all  the  way 
between  those  applying  to  FeS  and  those  applying  to  FeS2. 

The  structure  of  the  ore  is  the  same  as  that  of  the  graphitic 
rock,  with  the  same  variations  in  the  ore  as  to  contents  in  sul- 
phides, as  there  are  in  the  country-rock  as  to  contents  in  carbon- 
matter.  That  in  no  case  I  have  met  with  a  nucleus  of  carbon 
in  a  body  of  sulphides,  I  have  attributed  to  a  full  completion 
of  the  metamorphosis. 

Yet  another  feature  is  common  to  the  ores  of  the  described 
deposits.  For  a  long  distance  on  the  northern  part  of  these 
continental  deposits,  wherever  they  occur  in  the  Huronian 
schists,  their  ores  carry  nickel  in  proportions  varying  from  a 
mere  trace  in  the  copper-metal  made  therefrom  to  an  available 
percentage  in  the  ore  itself. 

Although  much  disinclined  to  draw  generalizing  conclusions 
from  isolated  geognostic  phenomena,  I  claim  justification  in  the 
case  at  hand  for  the  following  conclusions,  because  the  evidence 
is  such  as  repeats  itself  on  a  large  area,  and  once  understood 
presses  itself  upon  our  attention,  so  as  to  be  no  longer  ignored  : 

1.  The  iron  and  copper  sulphides  occurring  in  the  Huronian 
crystalline  schists  on  the  eastern  part  of  the  North  American 
continent  have  locally  displaced  carbonaceous  matter,  where 
faulting  of  strata  aided  water-circulation,  such  water  containing 
sulphate  salts  of  the  metals  in  solution. 

2.  The  metamorphic  action  of  absorbing  mineral  carbon  and 
of  setting  free  C02  is  continuous  to  the  present  day. 

3.  The    product  of  such   action    extending  below  sea-level 
being  observable  in  lines  nearly  parallel  with  the  coast-line  of 
an  entire  continent,  and  showing  equal  peculiarities  in  com- 
position on  the  entire  line,  it  is  reasonable  to  assume  oceanic 
action. 

It  is  true  that  the  ocean  of  our  period  evinces  the  presence 
of  copper  only  by  its  presence  in  maritime  organisms.  But 
when,  on  the  shores  of  a  once  existing  Triassic  sea  we  find  em- 
bedded in  massive  but  porous  sand-rock  an  entire  palm-vegeta- 
tion, that  has  turned  into  copper-glance,  as  my  eyes  have  seen 
it  (compare  p.  131  of  Prof.  Posepny's  paper),  then  we  may  well 
assume  the  presence  of  a  perceptible  quantity  of  copper  in  a 


210  THE    GENESIS    OF    ORE-DEPOSITS. 

Triassic  sea,  though  not  necessarily  sufficient  to  destroy  animal 
life.  It  is  even  a  matter  of  time  only  for  an  ocean  like  the  one 
of  our  own  period  to  provide  Pecillopora  and  Heteropora  corals 
with  their  copper,  or  to  be  the  means  of  metamorphosis  of  car- 
bon-deposits into  copper-sulphides  in  part;  the  percentage  of 
copper  in  these  deposits  being  in  general  not  above  three  per 
cent,  of  the  deposits  as  a  whole. 

I  find  a  further  justification  for  stating  these  facts  and  the 
conclusions  to  which  they  lead  in  the  circumstance  that  the 
learned  author,  although  mentioning  the  occurrence  of  graphite 
in  crystalline  schists,  does  not  mention  that  this  graphite  any- 
where accounts  for  the  origin  of  ore-beds. 

The  description  of  the  Sudbury  ore-beds  deals  with  a  case 
far  more  complicated  than  those  considered  by  me,  because 
there  Huronian  strata  similar  to  those  met  at  the  different 
mines  in  the  Appalachians  have  been  disturbed  by  more  recent 
dioritic  eruptions,  which  subjected  the  pre-existing  ore-beds  to 
a  new  partial  or  second  metamorphosis,  by  which  the  true  state 
of  affairs  is  very  materially  obscured,  misleading  the  describers 
into  the  untenable  assumptions,  so  justly  controverted  by  the 
learned  author.  Had  he  been  informed  of  the  facts,  as  I  have 
described  them  above,  the  author  of  this  eminently  interesting 
and  progressive  essay  on  the  genesis  of  ore-deposits  would  have 
been  able  to  knock  the  last  crutch  from  under  the  theory  of  an 
eruptive  origin  of  the  ore-deposits  at  Sudbury  and  elsewhere  in 
the  crystalline  rocks  of  the  Huronian  period. 

I  take  this  opportunity  to  furnish,  on  another  point,  informa- 
tion for  which  Prof.  Posepny  apparently  calls  (p.  132). 

A  few  months  only  after  my  report  on  the  Nacimiente  copper- 
occurrence  was  published,  with  the  consent  of  those  interested, 
in  the  Engineering  and  Mining  Journal,  Aug.  7  and  14, 1880,  the 
United  States  surveyors,  who  were  commissioned  by  the  Sur- 
veyor-General of  New  Mexico  to  survey  the  twenty-one  mining 
claims  described  by  me,  were  driven  off  these  claims  by  a 
numerous  band  of  jumpers,  who  had  swarmed  into  those  parts 
as  the  usual  avant-garde,  indicating,  as  stormbirds  the  storm, 
the  approach  of  a  new  railroad  line  in  those  remote  parts.  To 
reinstate  the  legitimate  owners  either  brutal  force  or  litigation 
had  to  be  employed.  The  ill-success  of  other  copper-enterprises 
in  New  Mexico,  though  quite  foreign  to  all  natural  conditions, 


THE    GENESIS    OF    ORE-DEPOSITS.  211 

caused  them  to  resort  to  neither.  When,  in  1891,  I  again 
visited  the  upper  Rio  Grande  valley,  I  found  on  the  platform 
of  the  railroad-station  at  Bernalillo,  N.  M.,  about  a  car-load  of 
the  precise  cuprified  palm-vegetation  formerly  described  by  me, 
showing  that  there  had  survived  some  activity  at  IsTacimiento ; 
but,  as  stated  in  my  first  report,  profitable  operations  are  possi- 
ble only  on  a  scale  like  that  on  which  lead  is  obtained  from  a 
similar  sand-rock  at  Mechernich  in  Rhenish  Prussia. 


Discussion  at  the  Virginia  Beach  Meeting,  February,  1894, 
Including  Communications  Subsequently  Received. 

T.  A.  RICKARD,  Denver,  Colorado  (communication  to  the 
Secretary) :  The  paper  of  Professor  Posepny  was  printed  so 
short  a  time  before  the  Chicago  meeting  that  it  could  not  re- 
ceive at  that  meeting  the  thorough  discussion,  based  upon  care- 
ful study,  which  its  great  importance  and  value  deserved.  In 
the  remarks  which  I  made  on  that  occasion,  I  could  do  little 
more  than  express,  with  others,  our  thanks  to  the  distinguished 
author  for  this  admirable  treatise  on  a  subject  of  such  general 
and  permanent  interest.  Further  examination  of  it  has  con- 
firmed the  opinion  that  its  appearance  marks  an  epoch,  par- 
ticularly in  this  country,  in  the  study  of  ore-deposits  and  their 
origin,  and  has  led  me  to  feel  that  our  appreciation  of  it  will  be 
best  expressed  in  aiding  its  purpose  and  widening  its  usefulness 
by  the  free  contribution  of  facts  and  interchange  of  views  which 
it  invites. 

I  have,  elsewhere,*  expressed  some  dissatisfaction  with  the 
new  names  introduced  in  this  paper ;  and  it  has  seemed  to  me, 
also,  that  the  classification  of  ore-deposits,  which  it  proposes,  is 
unnecessarily  complicated.  From  the  stand-point  of  a  mining 
engineer,  we  have  had,  in  my  judgment,  no  classification  more 
practical  and  sensible  than  that  suggested  by  Dr.  Raymond, 
twenty-five  years  ago  (outlined  on  page  7  of  Professor  Posepny's 
paper).  If  any  modification  of  it  be  permissible,  I  would  sug- 
gest the  following : 

*  Eng.  and  Min.  Jour. 
14 


212  THE   GENESIS    OF    ORE-DEPOSITS. 

I.  Surface-Deposits. 

A.  Due  to  mechanical  agencies. 

B.  Due  to  chemical  agencies. 
II.  Inclosed  Deposits. 

A.  Bedded. 

a.  Contemporaneous,  in  origin,  with  country-rock. 

b.  Subsequent,  in  origin,  to  country-rock. 

B.  Not  bedded. 

a.  Due  to  dislocation. 

b.  Due  to  impregnation. 

Surface-deposits  have  no  regular  form,  and  are,  therefore, 
distinguished  primarily  by  their  origin.  Class  A  would  be 
typified  by  gold-bearing  placers,  and  Class  B  by  deposits  of 
bog  iron-ores. 

When  we  come  to  inclosed  deposits,  we  find  an  extreme 
complexity ;  but,  we  readily  recognize  that  some  are  conform- 
able to  the  bedding  of  the  country-rock,  while  others  are  inde- 
pendent of  it.  We  can  further  distinguish  those  which  are  of 
contemporaneous  origin,  such  as  the  coal-beds,  from  those 
which  were  formed  after  the  deposition  of  the  country-rock. 
To  this  class  belong  ore-deposits  which  have  replaced  beds  of 
limestone ;  and  another  pretty  example  is  afforded  by  the  Ben- 
digo  saddle-reefs,  which  are  conformable  to  the  anticlinal  curves 
of  the  country-rock,  but  were  clearly  formed  after  both  the 
original  sedimentation  and  the  subsequent  folding. 

Among  the  non-bedded  deposits  there  is  no  limit  to  diversity 
of  structure  and  of  origin.  We  recognize,  however,  that  the 
fissure-veins  which  cut  across  the  bedding,  but  retain  a  definite 
position  due  to  their  formation  along  lines  of  original  disloca- 
tion, may  be  distinguished  from  the  irregular  impregnations, 
due  as  much  to  the  chemical  composition  of  the  country-rock 
as  to  its  structure.  These  two  types,  however,  are  forever  in- 
termingled. It  is  seldom,  indeed,  that  an  ore-deposit  has  not 
some  features,  however  faint,  of  form  and  structure  dependent 
upon  those  of  the  country-rock,  while,  on  the  other  hand,  it  is 
not  often  that  a  fissure-vein  is  found  which  does  not  exhibit,  in 
places,  a  lack  of  definition,  due  to  metamorphic  action  upon  its 
inclosing  walls. 

In  the  discussion  of  the  origin  .of  fissures,  Prof.  Posepny  has 


THE    GENESIS    OF    ORE-DEPOSITS.  213 

touched  upon  a  point  which  has  been  the  subject  of  frequent 
debate.  I  fully  believe  that  dislocation  accompanies  the  forma- 
tion of  a  fissure,  and  that  a  movement  of  its  walls  is  often 
evinced  by  slickensides  and  striae.  Yet,  this  has  been  ques- 
tioned by  one  or  two  members  of  the  Institute  who  are  known 
to  be  both  accurate  and  experienced  observers.  The  question 
at  issue  is  a  vital  one,  if  we  desire  to  obtain  a  clear  idea  of  the 
mode  of  formation  of  mineral  veins.  It  has  been  denied  that 
the  striae  and  slickensides  observed  upon  the  walls  of  lodes 
necessarily  prove  that  movement  has  taken  place;  but  it  has 
never  been  clearly  shown  what  other  agency  did  form  them. 
Prof.  John  A.  Church  has  discussed  this  matter  in  a  most  in- 
teresting way,*  and  has  pointed  out  that  slickensides  may  be 
formed,  not  only  by  rubbing  but  also  by  "  deformation,  as 
when  a  plastic  substance  like  clay  is  forced  through  an  open- 
ing," and  again  by  deposition  in  fine  parallel  lines.  Recently, 
Prof.  Daubree  has  experimentally  proved  that  gases  under  high 
pressure  are  capable  of  producing  strise  upon  rock-surfaces,  f 
It  is  true  that  a  distinction  is  made  between  strise  and  slicken- 
sides, but  I  look  upon  the  two  as  the  work  of  the  same  agency. 
In  the  former  case  we  have  coarse  rubbing  due  to  large  par- 
ticles, and  in  the  latter,  fine  polishing  due  to  minute  particles. 
There  is  no  doubt,  however,  that  certain  structures  are  called 
strise,  which  are  to  be  ascribed  to  causes  other  than  those  usually 
supposed  to  produce  striae  and  slickensides.  As  I  write  I  have 
before  me  a  large  piece  of  rock,  the  surface  of  which  exhibits 
fine  parallel  lines,  which,  at  the  mine  (the  Hillside,  in  Yavapai 
county,  Arizona),  were  called  striae.  The  rock  was  part  of  the 
casing  of  a  cavity  found  in  the  hanging-wall  of  the  lode,  which 
traversed  a  quartzose  talc-schist.  Its  surface  has  been  covered  J 
by  a  series  of  siliceous  coatings,  doubtless  deposited  by  the 
mineral-bearing  waters  which  circulated  over  it.  The  precipi- 
tation took  place  along  certain  parallel  lines,  probably  marking 
the  direction  of  flow  of  the  circulating  waters,  and  the  resulting 
appearance  is  to  be  regarded  as  a  pretty  example  of  a  variety 


*  Eng.  and  Min.  Jour.,  April  30,  June  11  and  18,  1892. 

f  Bull.  Soc.  Geol.  de  France,  3  serie,  Feb.,  1891,  t.  xix.,  p.  313.  Comp.  rend. 
Acad.,  t.  cxi.,  stances  du  24  Nov.  et  4  Dec.,  1890.  Compt.  rend.  Acad.,  t.  cxii., 
stance  du  19  Jan.,  1891. 

I  As  shown  by  viewing  the  broken  edges  of  specimens. 


214 


THE    GENESIS    OF    ORE-DEPOSITS. 


of  crustification,  but,  coming  as  it  does  from  a  lenticular  hole, 
cannot  have  been  due  to  rubbing  caused  by  faulting. 

In  the  accompanying  drawing  (Fig.  1),  reproduced  from  a 
sketch  made  underground,  the  cavity  above  referred  to  is 
marked  A.  There  are  two  others,  B  and  F,  of  the  same  kind. 
D  is  a  seam  6  inches  thick,  of  white  talcose  gouge,  lining  the 
foot-wall,  and  separating  it  from  C,  which  is  the  lode  itself. 


Fig.  I 

HILLSIDE  MINE,  ARIZONA 

The  latter  is  15  to  18  inches  wide,  and  consists  of  quartz,  iron- 
pyrites,  zinc-blende,  and  a  little  galena,  very  much  intermingled, 
and  carrying  gold  and  silver  in  almost  equal  proportions.  The 
lode  itself  reproduces  to  a  noticeable  extent  the  structure  of  the 
country-rock  which  it  has  replaced.  The  cavities  in  the  hang- 
ing-wall are  also  surrounded  by  talc-schist,  which  is  mineral- 
ized to  such  a  degree  as  to  constitute  "  low-grade  ore."  The 
vein  cuts  clear  through  the  foliation,  nearly  horizontal,  of  the 


THE    GENESIS    OF    ORE-DEPOSITS.  215 

talc-schist,  and  the  alteration  of  the  country-rock,  while  most 
marked  in  C,  extends  to  a  varying  distance  on  either  side. 

ISTot  infrequently  the  quartz  of  a  lode  has  striated  markings 
which  are  but  the  negative  of  those  occurring  on  the  wall- 
rock.*  In  such  cases  the  quartz  is  sometimes  entirely  solid 
and  unbroken,  suggesting  that  it  was  deposited  upon  the  pre- 
viously striated  surface,  and  that  it  has  not  only  replaced  the 
substance  but  also  reproduced  the  structure  of  the  rock  once 
inclosed  by  the  fissure-walls.  On  the  other  hand,  one  instance 
may  be  cited  where  it  seems  necessary  to  suppose  that  move- 
ment took  place  subsequently  to  the  deposition  of  the  quartz. 
At  the  1800-foot  level  in  the  Great  Extended  Hustler's  minef 
at  Bendigo,  Australia,  the  quartz  lying  against  the  hanging- 
wall  of  the  reef  exhibited  a  surface  as  smooth  as  polished 
ivory,  but  distinctly  grooved,  and  also  marked  with  fine,  dark 
lines,  parallel  to  the  grooves.  The  latter  had,  I  believe,  an 
origin  similar  to  that  of  ordinary  striae,  while  the  dark  lines 
were  due  to  the  grinding  of  particles  of  pyrite  observable  in 
the  quartz.  Though  this  quartz  seemed  to  the  eye  as  hard  as 
adamant,  it  would  readily  crumble  away  when  pressed  between 
the  fingers.  It  had  been  crushed  to  the  consistency  of  com- 
mon table-salt,  which,  save  for  the  presence  of  occasional  crys- 
tals of  pyrite,  and  for  its  highly  polished  surface,  it  much  re- 
sembled. 

Objection  has  been  raised  to  accepting  the  occurrence  of  clay, 
strise  and  slickensides  as  necessary  evidence  of  faulting,  because 
they  are  occasionally  absent  where  movement  may  be  supposed 
to  have  taken  place.  In  such  instances,  it  is  reasonable  to  in- 
fer that  they  have  been  destroyed  by  agencies  identical  with 
those  to  which  the  lode-formation  is  due,  namely,  the  replace- 
ment of  country-rock,  often  in  a  crushed  and  shattered  con- 
dition, by  ore,  through  the  metamorphic  action  of  percolating 
solutions. 

There  is  a  fanciful  notion  current  among  miners  that  a 
smooth  wall  and  a  thick  gouge  are  the  necessary  adjuncts  of  a 
productive  "  true  fissure-vein."  Experience  does  not  confirm 
this  belief.  A  defined  wall  and  a  soft  seam  of  clay  are  natu- 

*  Instances  of  such  are  to  be  seen  in  the  gold-quartz  veins  of  California, 
f  See  Trans.}  vol.  xx.,  512,  et  seq. 


216  THE    GENESIS    OF    ORE-DEPOSITS. 

rally  welcome  to  the  miner,  because  they  facilitate  the  actual 
breaking  down  of  the  vein-stuff;  but  they  are  no  more  charac- 
teristic of  productive  than  of  barren  lodes. 

The  irregularity  in  the  dip  of  some  veins  has  been  cited  as 
disproving  the  possibility  of  their  formation  along  lines  of 
faulting.  Occasionally  mine-workings  show  that  the  dip  of  a 
vein  is  reversed;  and  the  formation  of  the  fracture  which  it 
occupies  cannot  be  referred  to  a  continuous  line  of  movement, 
because  that  would  have  involved  the  shearing-off  of  the  oppos- 
ing angle.  But  it  is  not  necessary  to  suppose,  nor  do  facts  sug- 
gest, that  lodes  are  generally  formed  along  continuous  or  single 
lines  of  movement.  As  Prof.  Posepny  has  well  shown,  it  is 
the  study  of  the  circulation  of  underground  waters  which 
affords  the  key  to  much  that  is  perplexing  in  ore-deposition. 
In  such  cases  as  are  here  referred  to,  it  is  rational  to  suppose 
that  the  mineralizing  solutions  searched  out  the  easiest  way 
which  offered  itself.  They  did  not  necessarily  percolate  along 
a  single  definite  straight  line  of  fissuring,  but  often  deviated 
from  it,  whenever  it  afforded  a  less  ready  passage  than  was 
offered  by  other  fractures  which  united  with  it  or  crossed  it. 
An  instance  which  occurs  to  me  as  I  write,  is  furnished  by  the 
Seven-Thirty  mine  at  Silver  Plume,  Colorado.  The  lode  con- 
sists of  a  system  of  veins  carrying  rich  silver-ore,  the  most 
productive  of  which  is  that  which  bears  the  name  of  the  mine. 
It  rarely  has  any  considerable  width ;  it  is  often  only  a  thread 
traversing  the  coarsely  crystalline  granitoid  gneiss  and  porphy- 
ritic  microcline  granite  of  the  region.  At  the  third  level,  about 
280  feet  from  the  surface,  there  is  a  very  marked  irregularity 
in  the  course  of  the  vein,  presenting  some  interesting  features, 
which  the  accompanying  sketch  (Fig.  2)  will  help  to  explain. 

From  the  shaft  eastward  for  several  hundred  feet  (A  to  B) 
the  vein  carries  ore ;  but  its  width  is  small  and  irregular.  The 
lode  widens  rapidly  at  B,  where  it  also  meets  with  a  sudden 
deviation  in  its  course.  At  a  first  glance,  this  looks  very  much 
like  a  fault,  but  subsequent  examination  will  correct  such  a 
view.  The  fissure  continues  in  a  straight  line  from  K  to  L, 
after  the  ore  has  swerved  to  the  south.  Instead  of  maintaining 
its  eastward  course,  the  ore  is  disposed  in  two  cross-veins,  CD 
and  EF,  nearly  at  right  angles  with,  that  course,  which  unite 
with  a  fissure,  MQ,  similar  in  character  and  parallel  in  strike 


THE    GENESIS    OF    ORE-DEPOSITS.  217 

to  that  from  which  they  sprung,  AL.  Both  AL  and  MQ  are 
continuous  so  far  as  they  have  been  followed  in  the  mine- 
workings.  The  walls  are  well-marked,  even  after  they  cease  to 
enclose  ore.  The  cross-veins  CD  and  EF  lack  well-defined 
boundaries.  The  western  branch,  CD,  is  a  streak,  about  3 
inches  wide,  carrying  ore  of  a  tenor  of  300  ounces  of  silver  per 
ton,  while  the  eastern  branch,  EF,  is  larger,  about  1  foot  wide, 
and  carries  ore  of  lower  grade,  about  100  ounces  per  ton.  The 
latter  is  accompanied  by  much  more  galena  than  the  former. 
The  distance  between  the  two  is  10  feet;  their  length  is  44 
feet.  The  country  separating  them  is  not  noticeably  altered  or 
mineralized. 

This  is  not  an  instance  of  faulting ;  the  ore  is  found  in  con- 
nection with  a  system  of  fractures  AB,  CD,  EF  and  MQ,  the 


E 


M 


*  P,  P    Q 

Fig.  2 

SEVEN  THIRTY  MINE,  COLORADO. 

varied  structure  and  arrangement  of  which  modified  the  circu- 
lation of  mineralizing  solutions,  and  so  brought  about  the  ir- 
regularity in  the  deposition  of  the  various  minerals  comprising 
the  ore.  The  mineralizing  waters  met  with  diverse  conditions. 
From  A  to  B  the  fissure  was  tight,  and  its  boundaries  were 
distinct,  limiting  the  circulation  to  a  narrow  channel ;  hence  a 
small  streak  of  ore  was  found.  At  B  the  shattering  of  the 
country-rock  accompanying  the  formation  of  the  cross-frac- 
tures, CD  and  EF,  offered  facilities  for  the  ready  penetration 
of  the  solutions  and  for  chemical  interchanges.  From  C  to  D 
and  from  E  to  F  the  irregular  fracture  across  the  foliation  of 
the  country-rock  produced  irregular  but  rich  streaks  of  ore. 
On  meeting  with  the  other  main  line  of  fissure  the  solutions 
again  found  well-defined  boundaries  which  put  a  check  to  the 
metamorphic  replacement  of  the  country-rock,  and  it  was  not 


218  THE    GENESIS    OF    ORE-DEPOSITS. 

till  the  conditions  changed  (at  0),  that  a  notable  width  of  ore 
was  again  deposited. 

Many  supposed  faults  found  in  mine-workings  are  really  of 
this  character.  There  has  been  a  deviation  in  the  course,  and 
a  marked  diminution  or  increase  in  the  amount  of  ore-deposi- 
tion, because  the  mineralizing  solutions  have  circulated  along 
those  fractures  which  presented  the  easiest  passage  and  offered 
the  conditions  most  favorable  to  chemical  interchanges. 

Returning  to  the  subject  of  striae,  slickensides  and  clay-seams, 
I  must  say,  that  while  the  questioning  of  accepted  theories  is 
wholesome,  and  the  views  quoted  above  deserve  respectful  con- 
sideration, it  seems  to  me  that  observed  facts  warrant  the  gen- 
eral belief  that  these  phenomena  have  usually  been  produced 
by  the  rubbing  of  two  faces  of  rock  which  have  undergone 
movement ;  and  I  do  not  sympathize  with  those  who  consider 
that  the  ordinary  explanation  is  far-fetched.  We  know  that 
the  rock-formations  of  the  upper  earth  have  undergone  move- 
ment, for  this  is  proved  by  all  geological  investigation.  Further, 
we  have  every  reason  to  believe  that  movement  among  beds 
of  rock  of  unequal  flexibility  must  cause  some  to  break.  Facts 
confirm  such  a  belief.  Again,  every  break  must  be  coincident 
with  a  movement:  for  a  fracture  can  hardly  be  said  to  exist 
until  made  evident  by  movement  however  slight.  At  any  rate 
a  fracture  unaccompanied  by  movement  would  not  give  the  re- 
lief required  by  a  series  of  beds  exposed  to  such  strain  as  ne- 
cessitated a  rupture.  Such  movement  must  be  accompanied  by 
friction,  due  to  the  tendency  to  smooth  down  the  irregularities 
of  the  two  opposing  rock-faces.  Where  movement  has  once 
occurred,  a  line  of  less  resistance  is  established,  an  da  repetition 
of  movement  is  likely.  The  result  is  to  break  small  particles 
from  off'  projecting  points  and  so  form  a  dust  which  water 
makes  into  mud  or  clay,  also  to  scratch  the  surfaces  in  contact, 
forming  strise,  and  to  polish  them,  forming  slickensides.  Why 
therefore  deny  the  probability,  even  the  necessity,  of  the  move- 
ment of  the  walls  of  a  fissure,  and  why  endeavor  to  give  to  the 
markings  of  rocks  underground  an  origin  other  than  the  one 
which  would  certainly  be  ascribed  to  them  if  they  were  found 
on  rocks*  at  the  surface  ? 

*  No  one  questions,  for  instance,  that  the  scratching  seen  on  boulders  from  a 
glacial  moraine  are  the  result  of  rubbing  due  to  movement. 


THE    GENESIS    OF    ORE-DEPOSITS.  219 

The  pages  which  Prof.  Posepny  devotes  to  an  inquiry  into 
the  conditions  governing  the  flow  of  underground  waters  are 
among  the  most  valuable  of  his  treatise.  His  explanations  will 
do  much  to  clarify  our  conceptions  of  the  mode  of  behavior  of 
underground  waters,  and  will  doubtless  suggest  further  inquiry 
in  the  same  direction.  The  word  "  circulation  "  is  the  key  to 
the  whole  matter.  There  has  been  a  tendency  to  speak  of  de- 
scending, lateral  and  ascending  currents,  as  though  the  one  ad- 
jective would  cover  the  manner  of  movement  of  all  mineral 
solutions.  An  ascending  flow  was  supposed  to  have  formed 
this  lode,  descending  that  one,  while  others  again,  steering  a 
middle  course,  have  imagined  that  ore-formations  derived  their 
origin  from  solutions  having  a  lateral  flow.  In  each  case  a  nar- 
row view  of  the  subject  is  both  unphilosophic  a^nd  unscientific ; 
it  has  too  often  been  the  obstacle  to  progress  in  this  branch  of 
geology.  One  great  fact  confronts  us,  and  that  is  circulation. 

The  distinguished  author  is  himself  carried  away  by  his 
prejudices,  and  in  the  latter  portions  of  his  treatise*  allows  his 
ascensionist  views  to  lead  him  too  far  and  in  part  to  forget  the 
very  forcible  teaching  given  in  the  earlier  pages.  Much  will 
be  done  to  explain  the  many  puzzling  and  apparently  contra- 
dictory features  exhibited  by  the  ore-deposits  of  different  re- 
gions if  we  remember  that  mineral  solutions  both  descend  and 
ascend,  that  occasionally  they  may  have  an  approximately  lat- 
eral flow,  and  that  in  each  instance  their  circulation  is  governed 
by  a  diversity  of  ever-changing  conditions. 

Water  must  first  descend  in  order  to  afterwards  ascend.  The 
known  density  of  the  earth  precludes  the  supposition  that  its 
interior  contains  any  reservoirs  of  water ;  the  sinking  of  deep 
wells  and  bore-holes  has  indicated  that  at  a  comparatively  short 
distance  from  daylight  the  temperature  is  so  high  that  water 
could  not  exist  as  such,  but  would  be  dissociated  into  its  con- 
stituent gases ;  while  actual  mining  exploration  has  shown 
that  in  the  deepest  mines  there  is  less  water  encountered  in 
depth  than  in  proximity  to  the  surface.  These  facts  all  con- 
firm the  every-day  observation  that  underground  waters  origi- 
nate from  the  rain  and  snow  precipitated  from  the  atmos- 
phere. 

*  As  on  page  57. 


220  THE    GENESIS    OF    ORE-DEPOSITS. 

We  may  compare  the  circulation  of  water  up  and  down, 
through  the  earth's  rocky  exterior,  to  that  of  the  ordinary 
heater  in  a  house.  The  water  circulates  because,  when  hot,  it 
rises  through  the  length  of  pipe,  and,  when  cool,  it  falls  hack 
to  he  reheated.  Using  this  analogy  to  explain  Nature's  oper- 
ations, we  have  at  one  end  the  condensation  and  precipitation 
of  moisture  due  to  a  fall  of  temperature,  while  at  the  other, 
and  deep  down  in  the  earth's  rocky  confines,  we  have  a  heat 
which  sends  the  water  back  to  the  surface.  In  this  matter  of 
ore-deposition  we  are  not  concerned  with  the  two  ends  of  the 
circuit.  "We  have  no  particular  interest  for  the  moment  in  that 
part  of  the  water-circulation  which  intervenes  between  its  ele- 
vation by  evaporation  from  the  earth's  surface  and  its  return  as 
rain;  nor,  on  tfye  other  hand,  can  we  see  what  goes  on  at  the 
other  end  of  the  circuit.  We  can  only  guess  what  conditions 
obtain  and  what  phenomena  occur  at  depths  inaccessible  to 
man.  All  our  investigations  must  concern  themselves  with 
the  intermediate  stage,  that  'stage  which  is  most  particularly 
marked  by  the  transition  from  higher  to  lower  temperatures, 
and,  inversely,  from  increasing  to  diminishing  pressures.  It  is 
the  nice  adjustment  of  these  conditions  which,  on  the  one  hand, 
favors  precipitation,  and,  on  the  other,  compels  solution.  To 
the  miner,  therefore,  it  may  appear  most  important  to  investi- 
gate those  factors  which  bring  about  precipitation,  because  to 
them  must  be  ascribed  the  immediate  agency  of  ore-deposition. 
It  would  simplify  his  ideas  if  he  could  speak  of  an  upper  zone 
of  precipitation,  where  the  temperature  is  low  and  the  pressure 
light,  in  contradistinction  to  a  lower  region  of  solution,  where 
the  heat  is  great  and  the  pressure  intense.  Such  attempts  to 
separate  the  locality  of  the  two  processes,  however,  must  not  be 
carried  too  far.  Precipitation  has  no  sooner  ceased  than  solu- 
tion begins.  It  is  the  excess  of  the  one  over  the  other  which 
causes  the  deposition  of  ore  in  one  place  and  its  removal  to  an- 
other. Similarly,  in  our  talk  of  "  primary  "  and  "  secondary  " 
deposits  of  ore,  while  some  such  distinction  may  be  necessary 
for  the  purpose  of  explaining  differences  of  immediate  origin, 
we  must  not  fail  to  recognize  that  all  the  ore-deposits  within 
the  ken  of  man  are  essentially  secondary.  There  has  been 
nothing  original  since  the  world  was  first  evolved  from  chaos. 
We  have  to  deal  with  a  continuous  rearrangement  of  material. 


THE    GENESIS    OF    ORE-DEPOSITS.  221 

The  ore  of  one  place  came  thither  by  removal  from  another. 
Whether  it  be  present  in  minute  microscopic  particles  or  in 
blocks  as  big  as  a  house,  is  a  distinction  more  economic  and 
commercial  than  scientific  and  philosophic.  The  decomposition 
of  one  mineral  is  required  for  the  composition  of  another. 
Ore-deposits  are  in  their  nature  concentrations,  whether  by  the 
mechanical  accumulation  of  disintegrated  fragments  of  older 
deposits  or  by  the  local  regathering  or  segregation  by  chemical 
agencies  of  minerals  previously  widely  and  minutely  dissem- 
inated, or  finally  by  the  addition,  bit  by  bit,  through  mechan- 
ical and  chemical  force,  of  the  matter  brought  from  above  or 
below  by  circulating  waters. 

The  frequent  occurrence  of  thermal  springs  in  the  neighbor- 
hood of  later  eruptive  rocks  is  very  properly  emphasized  by 
Prof.  Posepny,  and  is  of  immediate  importance  to  the  student 
of  ore-deposition  because  the  eruptive  rocks  are  in  turn  found  so 
often  in  close  association  with  lode-formations.  That  thermal 
springs,  eruptive  rocks  and  ore-deposits  are  intimately  inter-re- 
lated in  their  origin  is  generally  accepted.  In  this  connection 
I  may  be  permitted  to  contribute  some  additional  facts. 

Besides  the  localities  quoted  by  Prof.  Posepny,  I  would  men- 
tion the  Hauraki  or  Thames  gold-field,  in  the  North  Island  of 
New  Zealand,  where  a  good  opportunity  is  offered  for  the  study 
of  this  subject.  In  the  Coromandel  peninsula  of  the  North 
Island  there  is  a  gold-bearing  belt  extending  for  nearly  a  hun- 
dred miles,  from  Cape  Colville  to  Te  Aroha.  The  prevailing 
country-rock  consists  of  Tertiary  eruptives,  through  which 
patches  of  Carboniferous  slate  occasionally  appear.  There  are 
thermal  springs  scattered  throughout  the  region.  At  the  prin- 
cipal mining  center,  the  Thames,  the  escape  of  carbonic  acid 
gas  has  often  caused  a  temporary  cessation  of  work  in  the 
mines.  There  are  soda-water  springs  in  the  vicinity  of  the 
Thames.  At  Te  Aroha,  at  one  end  of  the  gold-belt,  there  is  a 
group  of  celebrated  medicinal  hot  springs.  This  last  locality 
is  connected  by  a  continuous  chain  of  thermal  springs  with 
Eotomahana,  about  45  miles  distant,  the  famous  hot-lake  re- 
gion, the  pink  and  white  sinter-terraces  of  which  were  known 
for  their  beauty  throughout  the  world  until  Mt.  Tarawera  broke 
out  in  sudden  eruption  and  destroyed  them  in  1884. 

Veins  of  gold-bearing  quartz,  recent  eruptive  rocks,  thermal 


222  THE    GENESIS    OF    ORE-DEPOSITS. 

springs,  dying  solfataric  action,  and  active  volcanic  force,  are 
all  intimately  associated  in  this  corner  of  the  world. 

At  the  Thames,  the  leading  mining  town  of  the  island,  bodies 
of  gold-ore  of  unusual  richness  have  been  found.  In  1871,  the 
Caledonia  mine  produced  10  tons  of  gold  and  paid  three  million 
dollars  in  dividends.  In  1878,  at  the  Moanataeri,  5400  pounds 
of  quartz  yielded  14,600  ounces  of  gold.  The  prevailing 
country-rock  is  an  andesite  breccia,  traversed  by  zones  of  de- 
composition, in  which  the  gold-veins  occur.  At  Rotorua,  in  the 
hot-lake  district  already  referred  to,  the  plain  is  in  part  covered 
with  fragmentary  andesite.  This  material  is  usually  loose  and 
unconsolidated.  Near  the  edges  of  the  fumaroles,  which  are 
numerous,  it  has,  however,  become  cemented,  and  then  very 
much  resembles  the  country-rock  of  the  mines.  The  rims  of 
the  fumaroles  also  exhibit  products  of  decomposition,  which 
are  similar  in  character  to  those  observed  in  the  lode-channels 
at  the  Thames,  and  which,  because  they  are  soft  and  granular, 
have  been  termed  "  tufaceous  sandstone."  Quartz  closely  re- 
sembling that  of  the  gold-veins  of  the  mines  can  also  be  seen 
to  be  deposited  around  certain  of  the  fumaroles  and  hot  springs 
referred  to  above.  My  examination  of  the  ore-occurrence  and 
vein-structure,  though  incomplete,  led  me  to  conclude  that  the 
deposition  of  the  gold  and  its  associated  minerals  had  followed 
certain  lines  of  altered  country-rock  which  had  been  exposed  to 
the  eifects  of  dying  but  lingering  solfataric  agencies.* 

Another  district  which  affords  evidence  to  help  us  in  study- 
ing this  subject  is  that  of  Pontgibaud,  in  south-central  France, 
among  those  volcanic  peaks  of  Auvergne  which  have  been  ren- 
dered classic  by  the  work  of  Poulet  Scrope.  The  silver-lead 
lodes  of  this  district  have  been  very  extensively  developed,  and 
their  geological  structure  has  more  than  once  received  notice 
at  the  hands  of  competent  observers. f  The  country-rock  con- 
sists of  gneiss  and  mica  schist,  penetrated  by  dikes  of  granulite.J 

*  See  also  "Certain  Dissimilar  Occurrences  of  G old-Bearing  Quartz,"  by  the 
writer,  in  the  Proceedings  of  the  Colorado  Scientific  Society  for  1893. 

f  Annales  des  Mines,  M.  Guenyveau,  1st  series,  t.  vii.,  p.  162  to  188.  MM. 
Eivot  and  Zeppenfeld,  4th  series,  t.  xviii.,  p.  137  to  257,  361  to  446.  Also  recently 
M.  Lodin,  April,  1892,  in  a  paper  entitled  "  Etude  sur  les  gites  metalliferes  de 
Pontgibaud,"  also  published  in  the  Annales  des  Mines. 

J  If  it  were  in  our  West  it  would  be  called  "  porphyry" — a  term  which  has 
gradually  been  losing  its  distinctive  meaning  through  careless  use. 


THE    GENESIS    OF    ORE-DEPOSITS.  223 

The  lodes  are  of  later  date  than  the  dikes,  but  older  than  the 
Pliocene  flows  of  basalt  which  cover  their  croppings.  The 
period  of  their  formation  is  considered  to  have  been  between 
the  middle  Miocene  and  the  middle  Pliocene,  very  probably 
contemporaneous  with  the  extension  of  the  acid  eruptives  of 
Mont  Dore,  which  took  place  at  the  beginning  of  the  middle 
Pliocene.  The  lodes  generally  follow  the  veins  of  granulite, 
and  are  productive  only  when  so  associated.  When  the  dike- 
rock  in  which  the  lode  occurs  is  most  feldspathic,  the  metallif- 
erous filling  is  most  valuable. 

In  this  region  mineral  springs  are  abundant,  and  the  escape  of 
carbonic  acid  gas  has  frequently  put  a  temporary  stop  to  under- 
ground work.  This  applies  particularly  to  that  part  of  the  dis- 
trict through  which  the  river  Sioule  flows  between  the  town  of 
Pontgibaud  and  the  mines  at  Pranal.  Often,  while  fishing  along 
the  stream,  I  have  noted  places  where  there  is  a  constant  escape 
of  carbonic  acid  gas  from  its  bed  to  the  surface.  At  Pranal 
there  appears  to  be  an  intimate  connection  between  the  lode- 
fissures  and  the  volcanic  vents.  One  of  the  mineral  veins  has 
been  traced  to  its  connection  with  what  appears  to  be  a  vent 
of  the  extinct  volcano  of  Chalusset.  Powerfully  carbonated 
springs  exist  close  to  the  mines  and  on  the  slope  of  Chalusset. 

In  both  of  the  two  districts  above  cited,  the  one  in  New  Zea- 
land and  the  other  in  France,  note  has  been  made  of  the  escape 
of  considerable  quantities  of  carbonic  acid  gas.  It  is  scarcely 
necessary  to  emphasize  the  fact  that  this  is  a  most  common  and 
powerful  agent  in  bringing  about  changes  in  rocks  and  minerals. 
The  action  of  carbonic  acid,  and  of  the  alkaline  carbonates 
which  it  forms,  have  been  recognized  by  all  petrographers. 
To  it  we  owe  the  salts  occurring  in  ordinary  mineral  springs ; 
to  it  are  due  the  pseudomorphic  replacement  of  feldspar  with 
chlorite*,  and  the  alteration  of  olivine  into  serpentine,  and  of 

*  And  the  chlorite  afterwards  gives  place  to  tinstone.  This  is  a  subject  much 
studied  by  Mr.  Richard  Pearce,  at  a  time  when  its  importance  was  not  so  well  rec- 
ognized as  now. — See  "The  Influence  of  Lodes  on  Rocks,"  Proceedings  of  the 
Mining  Association  of  Devon  and  Cornwall,  September  8,  1864.  Mr.  Pearce  directs 
attention  to  the  difference  between  the  granite  encasing  the  lode  and  that  found 
at  some  distance  from  it.  He  makes  note  of  the  joints  in  the  granite,  and  remarks 
upon  the  difference  in  the  minerals  found  in  two  well-marked  systems  of  joints 
having  contrary  directions.  He  shows  that  the  changes  observed  in  the  rock  ad- 
joining the  lodes  have  their  origin  in  the  lodes.  Emphasizing  the  metamorphism 


224  THE    GENESIS    OF    ORE-DEPOSITS. 

limestone  into  dolomite.  Even  at  ordinary  temperatures,  car- 
bonated waters  extract  magnesia  from  complex  silicates.  In 
this  way,  biotite  loses  magnesia  and  iron,  becoming  converted 
into  muscovite. 

The  subject  of  the  close  association  of  ore-deposits  and  igne- 
ous rocks  is  a  most  important  one  to  mining  engineers.  The 
detailed  geological  surveys  of  several  of  the  most  productive 
mining  districts  of  the  West,  carried  out  during  the  past  few 
years,  have  done  much  to  emphasize  the  relation  which  seems 
to  exist  between  bodies  of  eruptive  rocks  and  deposits  of  gold- 
and  silver-ore  found  close  to  them.  It  has  become  the  fashion, 
especially  since  the  publication  of  Emmons's  masterly  mono- 
graph on  the  Leadville  region,  to  suppose  that  the  precious 
metals  of  the  lodes  were  derived  from  the  leaching  of  the  adja- 
cent eruptives ;  and  some  mining  engineers  have  gone  so  far  as 
to  consider  the  neighborhood  of  dikes  necessary  to  the  occur- 
rence of  a  productive  lode.  This  latter  notion  may  be  classed 
with  the  supposition,  now  slowly  passing  away,  which,  not  long 
ago,  was  so  strong,  that  a  "  true  fissure-vein  "  was  the  only 
permanent  depository  of  the  precious  metals. 

In  the  United  States,  in  Europe,  and  in  most  of  the  Austral- 
asian mining  regions,  the  close  association  of  dikes,  or  other 
forms  of  intrusive  eruptive  rocks,  with  lode-forrnations  is  so 
marked,  that  it  is  not  surprising  to  find  such  rocks  considered 
as  necessary  adjuncts  to  the  occurrence  of  valuable  ore-deposits. 
But  generalizations  are  proverbially  dangerous ;  and,  that  this 
is  an  illustration  of  the  proverb,  the  following  facts  may  show. 

The  gold-mining  region  of  the  province  of  Otago,  in  the 
South  Island  of  New  Zealand,  is  confined,  for  the  most  part,  to 
a  great  series  of  foliated  quartzose  schists  of  an  age  considered 
Archaean  by  some,*  and  Silurian  by  others,  f  These  rocks  have 

of  the  granite,  he  shows  that  the  lodes  consist  essentially  of  altered  granite,  the 
most  important  alteration  being  the  replacement  of  the  feldspar  by  chlorite,  by 
tinstone  and  by  schorl.  He  discards  the  idea  of  an  igneous  origin  of  the  tin-ore, 
and  declares  that  aqueous  agency  alone  can  satisfactorily  account  for  the  changes 
in  the  rocks  and  the  formation  of  the  lodes.  He  expresses  the  belief  that  the 
subject  of  the  metamorphism  of  the  country-rock,  if  "diligently  investigated, 
must  assist  in  explaining  some  of  the  laws  which  regulate  mineral  deposits."  This 
was  said  thirty  years  ago  ! 

*  "  On  the  Foliated  Rocks  of  Otago,"  Professor  F.  W.  Hutton,  F.G.S.  Trans, 
of  the  New  Zealand  Institute,  vol.  xxiv.,  1891. 

t  "  The  Gold-Fields  of  Otago."     Trans.  A.  I.  M.  R,  xxi.,  412. 


THE    GENESIS    OF    ORE-DEPOSITS.  225 

an  enormous  thickness  over  a  large  area;  the  thickness  has 
been  estimated  at  50,000  feet,  while  the  area  is  fully  10,000 
square  miles.  This  has  been  a  very  successful  gold-mining  re- 
gion, although  the  gravel-deposits  have,  so  far,  been  more  pro- 
ductive than  the  quartz-veins.  The  lodes  have  certain  well- 
marked  structural  peculiarities,  resulting  from  the  foliated 
arrangement  of  the  country-rock  which  they  traverse.  In  a 
previous  contribution,  incidental  reference  was  made*  to  the 
fact  of  the  remarkable  absence,  in  this  auriferous  area,  of  erup- 
tive rocks.  It  is  interesting  to  recall  so  marked  an  exception 
to  what  is  often  held  to  be  a  general  rule. 

That  the  quartzose  schists  of  Otago  are  simply  altered  sedi- 
mentary beds  of  very  early  geological  age,  there  is  little  reason 
to  doubt.  The  quartz  folia  are  arranged  along  the  lines  of 
original  sedimentation,  and  not  along  cleavage-planes.  It  is  a 
case  of  "  stratification-foliation,"  as  distinguished  from  "  cleav- 
age-foliation, "f  The  only  rock  likely  to  be  a  metamorphosed 
eruptive  is  the  chlorite  schist  of  Queenstown.J  The  mining 
regions  of  Otago  do  not  exhibit  any  of  the  phenomena  of  con- 
tact-metamorphism ;  and  the  changes  which  have  been  pro- 
duced may  be  ascribed  to  what  we  call  "  regional "  metamor- 
phism,  a  vague  way  of  describing  those  alterations  which  are 
forever  taking  place  in  rocks  wherever  there  is  heat  and  pres- 
sure, alterations  which  are,  therefore,  most  evidenced  by  the 
oldest  rocks,  which  have  necessarily  been  overlaid  by  a  great 
thickness  of  later-deposited  formations.  § 

A  treatise  which  covers  so  wide  a  field  as  that  of  Professor 
Posepny  can,  of  necessity,  devote  but  scanty  attention  to  some 
mining  regions  which,  to  those  who  know  them,  appear  to 
afford  important  evidence  on  the  subject  of  ore-deposition.  In 
this  regard,  it  is  to  be  regretted  that  Professor  Posepny  does 
not  seem  to  have  had  his  attention  drawn  to  certain  very  excel- 
lent geological  reports  contained  in  the  blue  books  of  the 

*  Trans.,  xxi.,  413. 

t  Prof.  T.  G.  Bonney  uses  these  terms  in  the  Quarterly  Journal  of  the  Geological 
Society,  vol.  xlix.,  part  i.,  p.  95. 

J  As  pointed  out  by  Prof.  Button.     Op.  cit. 

|  I  do  not  lose  sight  of  the  fact  that  igneous  rocks  may  become  schistose  by  met- 
amorphism,  especially  through  pressure,  as  a  dolerite  becomes  a  hornblende 
schist.  There  is  no  reason  to  suppose  that  such  a  metamorphism  has  occurred  in 
these  rocks  of  Otago. 


226  THE    GENESIS    OF    ORE-DEPOSITS. 

mining  departments  of  Victoria,  ~New  South  Wales,  and  ~New 
Zealand.  Australasia  has  many  object-lessons  to  offer  to  the 
student  of  economic  geology,  and  the  Colonial  geological  sur- 
veys have  published  several  accurate  and  most  interesting  de- 
scriptions of  them.* 

In  concluding  this  contribution  to  the  discussion  of  Prof. 
Posepny's  paper,  I  may  be  permitted  to  express  again  the  be- 
lief that  his  destructive  criticism  of  the  lateral-secretion  theory 
is  most  opportune,  and  that  his  investigations  into  the  flow  of 
underground  waters  will  do  much  to  illuminate  our  views  of 
the  methods  of  ore-deposition.  At  the  same  time,  I  cannot 
but  hold  that  his  accumulation  of  facts  and  observations  will 
show  that  neither  the  lateral,  nor  the  ascensionist,  nor  any  other 
one  narrow  theory  can  cover  the  multitudinous  diversity  of  the 
ways  in  which  ore-deposits  are  found  to  occur. 

R.  W.  RAYMOND,  New  York  City  :  Concerning  Mr.  Rickard's 
proposed  classification,  I  beg  to  say,  while  recognizing  its  con- 
venience for  mining  engineers,  that  it  cannot  be  considered  as 
a  substitute  for  that  of  Prof.  Posepny,  for  the  simple  but  con- 
clusive reason  that  it  is  not  genetic.  Its  fundamental  division 
is  based  upon  the  position  of  the  deposits,  which  should  be,  in 
a  genetic  classification,  a  subordinate  consideration ;  and  the 
most  profound  genetic  distinction  presented  by  nature,  namely, 
the  distinction  between  contemporaneous  and  subsequent  forma- 
tion, appears  in  this  scheme  as  a  division  of  the  third  degree, 
affecting  only  inclosed  bedded  deposits.  If  I  were  inclined  to 
criticize  names,  as  Mr.  Rickard  has  elsewhere  done  with  regard 
to  Prof.  Posepny,  I  might  point  out  that  the  word  "  contempo- 
raneous "  does  not  describe  coal-beds,  which  Mr.  Rickard  men- 
tions as  typical  examples  of  it.  Whatever  may  be  said  of  a 
coal-bed,  it  is  not  contemporaneous  in  origin  with  the  country- 
rock  above  it  or  below  it.  But  this  is  a  small  matter.  The 
point  I  make  is  much  more  important,  namely,  that  the  classi- 

*  I  would  more  particularly  instance  The  Geology  of  the  Vegetable  Creek  Tin- 
Mining  Field,  by  T.  W.  Edgworth  David,  and  the  recently  published  Special  Report 
on  theBendigo  Gold-Field,  by  E.  J.  Dunn,  together  with  the  numerous  observations 
made  by  K.  L.  Jack,  in  Queensland  ;  H.  Y.  L.  Brown,  and  H.  P.  Woodward,  in 
South  Australia ;  G.  H.  F.  Ulrich,  and  F.  W.  Hutton,  in  New  Zealand  ;  Wilkin- 
son and  Liversedge,  in  New  South  Wales  ;  Murray,  Sterling,  and  Howitt,  in  Vic- 
toria. 


THE    GENESIS    OF    ORE-DEPOSITS.  227 

fication  itself  is  neither  based  on  genetic  distinctions  nor  on 
any  other  logical  arrangement.  I  say  this  all  the  more  frankly, 
because,  as  Mr.  Rickard  declares  in  complimentary  pjirase,  he 
has  largely  followed  the  classification  given  by  me  in  1869. 
But  that  was,  as  Mr.  Rickard's  is,  merely  a  convenient  miners' 
arrangement.  Now  that  Prof.  Posepny  comes  forward,  pro- 
posing for  the  purposes  of  science,  not  of  mining,  a  truly  genetic 
classification,  a  critic  may  fairly  demonstrate  its  logical  defects 
and  suggest  remedies,  or  declare  remedies  to  be  impossible. 
In  the  latter  case,  his  contention  would  be  that  a  genetic  system 
cannot  be  constructed,  and  that  the  attempt  had  better  be 
abandoned.  But  to  say  that  one  prefers,  as  a  mining  engineer, 
the  handy  non-scientific  arrangement  of  ore-deposits  hitherto 
in  use,  is  no  criticism  at  all.  It  is  as  if  a  botanist,  considering 
a  natural  system  in  botany,  should  say  that  it  was  discourag- 
ingly  complicated,  and  that  he  preferred  the  simple  and  conve- 
nient arrangement  of  Linneeus,  by  which  one  could  identify  a 
species  from  the  number  of  petals  and  stamens  and  other 
arbitrary  signs. 

H.  Y.  WINCHELL,  Minneapolis,  Minn. :  While  heartily  agree- 
ing with  the  frequently-expressed  opinion  that  Prof.  Posepny's 
paper  is  a  masterly  and  exceedingly  important  discussion  of 
ore-deposits,  it  still  appears  that  there  may  be  room  for  differ- 
ences of  opinion  on  some  points.  Indeed,  they  necessarily 
follow  from  such  decided  statements  on  so  important  and  in- 
teresting a  subject. 

Those  of  us  who  live  in  the  Lake  Superior  region  are  wont 
to  believe  that  we  have  some  conception  of  the  meaning  of  the 
term  "  ore-deposits."  We  can,  and  frequently  do,  point  with 
pride  to  the  great  value  of  our  production  of  iron-ore  and  the 
fact  that  we  furnish  nearly  two-thirds  of  the  total  product  of 
the  United  States.  It  is  an  industry  employing  about  30,000 
miners  and  involving  capital  to  the  amount  of  fully  $100,000,- 
000.  But  when  we  come  to  treatises  on  iron-ore  deposits  we 
are  always  disappointed.  We  find  that,  while  speaking  gener- 
ally and  theoretically,  iron-ore  deposits  may  be  mentioned,  yet 
when  it  comes  to  critical  discussion,  and  the  illustration  of 
theories  by  examples,  they  are  omitted.  We  are  constrained 
to  protest  that  "  ore-deposit "  does  not  signify  merely  a  vein 

15 


228  THE    GENESIS    OF   ORE-DEPOSITS. 

of  gold-,  silver-  or  lead-ore  or  a  stockwork  of  tin-  or  zinc-ore, 
but  that  hematite  and  magnetite  form  ore-deposits  of  a  com- 
mercially, important  and  genetically  highly  interesting  class. 

The  value  of  the  raw  iron-ore  produced  in  this  country  in 
1889  was  equal  to  the  value  of  the  gold  bullion  produced  in  the 
same  year.  And  if  we  take  the  value  of  the  pig-iron,  which 
more  nearly  corresponds  with  bullion  in  the  degree  of  removal 
from  the  raw  material,  we  find  it  equal  to  the  value  of  the  gold 
and  silver  combined.  And  yet  our  author  dismisses  the  entire 
subject  in  a  couple  of  pages,  and  of  Fuchs's  and  DeLaunay's 
2000  pages  only  two  are  devoted  to  the  most  important  iron- 
ore  district  on  the  globe. 

It  would  not  be  fair  to  suggest  that  iron-ores  are  overlooked 
because  they  do  not  seem  to  be  explainable  by  the  theories 
adopted  for  other  classes  of  deposits.  If  that  were  the  case,  all 
the  more  need  of  giving  them  attention.  It  is  more  probable 
that  it  is  because  of  the  recentness  of  their  development  and 
the  comparatively  scant  literature  on  the  subject  in  the  libraries 
of  our  foreign  colleagues. 

That  the  circulation  of  waters  carrying  different  chemical 
reagents  is  the  all-important  factor  in  the  genesis  of  ores,  as  we 
find  and  mine  them,  is  clearly  shown  by  Prof.  Posepny,  and  is 
accepted  by  the  majority  of  writers  on  the  subject.  But  the 
prominence  which  is  given  to  ascending  waters  and  the  insig- 
nificant effects  ascribed  to  descending  solutions  will  not  find 
such  ready  acquiescence.  It  seems  likely  that  ascending  waters 
are  the  more  likely  to  be  effective  and  to  predominate  below 
the  ground-water  level  than  in  the  vadose  circulation.  But  it 
can  be  conclusively  demonstrated  that  many  of  the  immense 
iron-ore  lenses  of  the  Lake  Superior  region  owe  their  present 
state  of  concentration,  even  to  the  depth  of  many  hundreds  of 
feet,  to  the  action  of  the  descending  waters.  Aside  from  the 
Mesabi  range,  the  proofs  lie  partly  in  the  following  well-known 
facts  : 

1.  The  ore  is  a  product  of  concentration  in  situ,  whether  the 
original  rock  or  lean  ore  was  an  oxide,  a  silicate,  or  a  carbon- 
ate, or  whether  it  was  oceanically  or  otherwise  precipitated. 

2.  The  ore-bodies  have  the  shape  of  highly-inclined  lenses, 
and  frequently  have  an  unaltered  "  capping"  of  jasper  partially 
covering  their  upper  ends. 


THE    GENESIS    OF    ORE-DEPOSITS.  229 

3.  When  this  capping  is  present,  it  can  be  traced  downward 
into  the  ore  through  changes  which  are  clearly  the  result  of 
oxygenated  atmospheric  waters. 

4.  The  downward  course  of  the  waters  is  further  shown  by 
the  protecting  action  of  dikes  and  other  impervious  barriers, 
below  which  the  ore  is  not  found. 

5.  The  ore-lenses  lie  in  basins  of  greenstone-schists  or  other 
rocks,  and  occur  at  various  depths  to  at  least  2000  feet. 

6.  At  the  lower  edges  of  some  of  these  lenses  are  found  de- 
posits of  silica,  kaolin,  etc.,  which  have  plainly  been  removed 
from  the  ore-body  above  in  the  process  of  concentration. 

This  is  much  below  the  vadose  circulation,  as  the  immense 
pumping  engines  and  the  rivers  of  water  which  they  throw 
the  year  round  testify ;  but  it  is  an  instance  of  the  formation 
of  ore-deposits  on  the  largest  scale  by  descending  waters. 

The  circumstances  are  somewhat  different  on  the  Mesabi 
range,  but  the  proof  is  no  less  clear  that  the  ore  has  been 
formed  by  solutions  percolating  downward.  There  the  mines 
lie  along  the  south  side  of  the  continental  divide  or  water-shed, 
from  which  waters  flow  north  to  Hudson  Bay  and  south  to  the 
Gulf  of  Mexico.  They  thus  occupy  the  highest  regions  of  the 
northern  part  of  the  State.  Moreover,  the  shape  of  the  strata, 
and  the  presence  of  a  conglomerate  beneath  them,  indicate 
that  there  was  a  shore-line  there  when  the  rocks  were  deposited. 
These  facts,  with  the  comparatively  undisturbed  condition  of 
the  strata,  lead  us  to  believe  that  the  conditions  have  remained 
during  many  geological  ages  as  they  were  originally  and  as 
they  are  now,  viz.,  such  that  the  inevitable  direction  of  water- 
circulation  would  be  downward  and  following  to  a  certain  ex- 
tent the  gentle  dip  of  the  rocks  to  the  south. 

Although  of  remarkable  magnitude  and  chemical  purity, 
these  deposits  are  essentially  surface-products  and  are  at  pres- 
ent largely  above  the  ground-water  level.  The  processes  of 
replacement  by  the  removal  of  silica,  and  of  concentration  by 
the  addition  of  sesquioxide  of  iron,  can  be  seen  in  progress  in 
a  hundred  places.  The  rock  'which  undergoes  this  change  is  a 
gray,  reddish  or  greenish  chert  ("  taconite  ")  banded  with  iron- 
ore.  Figs.  1  and  2,  taken  from  specimens  from  the  Mesabi, 
illustrate  the  change  mentioned,  and  show  the  downward  course 
of  the  ferruginous  solutions. 


230  THE    GENESIS    OF    ORE-DEPOSITS. 

Since  we  have  here  examples  of  iron-ore  deposits,  both 
above  and  below  the  ground-water  level,  which  have  been 
formed  by  descending  waters,  the  thought  naturally  arises 
that  the  solutions  may  not  have  been  so  universally  ascend- 
ing, in  the  case  of  other  mineral  deposits,  as  our  author  would 
have  us  believe. 


Taconite  from  the  Mesabi  range  changing  to  iron-ore  by  solutions  moving  from 
left  to  right,  a  b  is  a  fault  line  which  conducted  the  descending  waters  downward 
and  prevented  the  right  half  of  the  specimen  from  undergoing  the  ferrification 
which  is  seen  in  the  left  half. 


Another  idea  on  which  undue  stress  seems  to  have  been  laid 
is  the  correctness  of  the  "  ascension  theory,"  and  the  absolute 
error  of  that  of  "  lateral  secretion."  A  consideration  of  these 
two  ideas  leaves  me  with  the  impression  that  they  are  not  in 
reality  so  diametrically  opposite  that  if  one  is  true  the  other 
can  have  no  scintilla  of  truth  in  it.  In  the  deep  region  the  cir- 
culating waters  are  supposed  to  be  under  considerable  pressure, 
from  which  they  escape  by  flowing  in  the  direction  in  which 


THE    GENESIS    OF    ORE-DEPOSITS. 


231 


they  meet  the  least  resistance.  Even  if  the  solution  were  on 
the  whole  ascending,  still  it  must  often  happen  that  cracks  and 
fissures  would  be  encountered,  leading  in  a  lateral  direction  into 
some  main  fissure,  full  of  ascending  waters  under  slightly  less 
pressure  than  that  behind  the  waters  which  entered  laterally. 
In  that  case  it  is  also  quite  likely  that  there  would  be  a  dif- 
ferent chemical  reaction  at  or  near  the  junction  of  these  two 


Another  instance  of  partial  alteration  of  taconite  to  ore.  There  was  a  joint  here 
along  a  b  whence  downward  moving  waters  effected  a  more  rapid  change  for  some 
distance  laterally  than  the  solutions  percolating  toward  this  joint  along  the  strata 
from  left  to  right  were  able  to  produce  in  the  solid  rock.  Specimen  collected  by 
J.  E.  Spurr. 

circulating  fluids  from  that  produced  by  the  action  of  either 
one  of  them  on  the  rocks  through  which  it  passed.  This  might 
result  in  the  precipitation  of  certain  minerals  on  the  walls  of 
the  main  fissure  near  the  subsidiary  fissure,  and  thus  the  re- 
sulting ore-deposit  would  owe  fully  as  much  to  lateral  secretion 
as  to  ascension.  And  if  these  lateral  joints  and  cracks  (or 
even  more  porous  rocks)  were  sufficiently  numerous,  the  whole 


232  THE    GENESIS    OF    ORE-DEPOSITS. 

vein,  when  formed,  would  be  due  to  the  combined  actions  of 
lateral  secretion  and  ascension. 

Moreover,  it  seems  almost  necessary  for  the  ascensionists  to 
borrow  aid  from  the  lateral  secretionists,  whether  they  will  or 
no.  For  the  question  arises :  Where  do  the  ascending  solutions 
come  from,  anyhow  ?  Is  there  an  inexhaustible  reservoir  at 
the  bottom  of  each  vein-fissure  which  supplies  a  ceaseless  flow 
of  carbonated  and  mineralized  waters  carrying  precious  metals 
in  solution  ?  Or  does  the  water  start  from  the  surface  and  per- 
colate downward  until  it  is  forced  by  heat  and  generated  gases 
to  rise  again  ?  If  the  latter  is  the  true  supposition,  is  it  not 
evident  that  the  fissures  which  conduct  these  ascending  waters 
must  receive  them  from  all  sides  through  a  thousand  small 
crevices  and  pores,  thus  making  again  a  combination  of  both 
lateral  and  ascending  motions  and  depositions  ? 

If  ascending  waters  come  from  a  great  depth,  descending 
waters  must  reach  to  the  same  great  depth,  and  since  the  solu- 
tions cannot  traverse  the  same  path  in  their  ascent  .that  they  do 
in  their  descent  there  must  be  a  certain  amount  of  lateral  mo- 
tion at  the  moment  when  these  solutions  are  the  most  dense 
and  carry  their  heaviest  burden  of  dissolved  material.  And 
it  is  evident  that,  whatever  the  depth  from  which  the  metallic 
elements  come,  there  is  as  much  chance  for  one  mode  of  depo- 
sition as  for  the  other. 


SECRETARY'S  NOTE. — The  remaining  contributions  to  the  dis- 
cussion published  in  this  volume  were  presented  at  the  Bridge- 
port Meeting,  October,  1894,  or  issued  with  the  papers  of  that 
meeting,  having  been  received  before  the  Florida  Meeting  of 
March,  1895. 

PROF.  POSEPNY  (communication,  translated  by  the  Secretary) : 
First  let  me  express  my  warmest  thanks  to  all  those  who  have 
so  favorably  judged  my  paper  on  the  "  Genesis  of  Ore-Deposits," 
and  likewise  to  those  who  have  taken  this  occasion  to  bring 
forward,  whether  in  support  of  my  views  or  in  opposition  to 
them,  various  observations  and  opinions,  whereby  our  knowledge 
of  ore-deposits  has  been  unquestionably  increased. 

It  is  exceedingly  difficult — indeed,  almost  impossible — to 
make  a  correct  comprehensive  statement  of  a  subject,  the  sep- 


THE    GENESIS    OF    ORE-DEPOSITS.  233 

arate  fundamental  data  of  which  are  scattered  throughout  the 
world ;  and  my  treatise  must,  of  course,  be  considered  as  merely 
an  attempt  in  that  direction,  inspired  by  the  purpose  of  con- 
tributing to  this  theme  an  element  not  yet  sufficiently  recog- 
nized, namely,  the  logical  application  throughout  of  the  genetic 
principle.  As  I  indicated  on  p.  9  of  this  volume,  I  expected 
as  a  result  neither  a  simplification  of  systems  nor  a  direct  ben- 
efit to  practice.  My  object  was,  irrespective  of  such  considera- 
tions, to  approach  more  nearly  to  the  truth. 

A  single  observer  may  be  able  to  establish  a  few  more  or  less 
important  facts ;  but  the  great  mass  of  the  knowledge  required 
he  cannot  personally  possess.  In  the  most  favorable  case,  gov- 
ernment institutions,  established  to  benefit  single  nations,  or 
scientific  or  business  associations,  may  procure  accurate  knowl- 
edge of  the  mineral  resources  of  separate  countries,  and  these 
may  be  combined  to  increase  the  knowledge  of  a  considerable 
territorial  complex;  but  the  question  still  remains,  whether  the 
developments  and  natural  exposures  in  a  given  region  are  really 
typical  and  conclusive  as  a  basis  for  general  scientific  deduc- 
tions. In  this  respect,  an  international  union  of  such  endeav- 
ors, devoted  to  the  advancement  of  this  branch  of  geology, 
would  be  a  decisive  gain. 

When  the  United  States  Geological  Survey  began  the  study 
of  the  geological  relations  of  ore-deposits,  there  was  ground  for 
hope  that  a  new  era  in  the  knowledge  of  this  subject  would  be 
thereby  inaugurated.  In  fact,  several  monographs  of  inestima- 
ble value  concerning  the  most  important  ore-deposits  had  been 
published,  when,  for  reasons  unknown  to  me,  the  whole  activ- 
ity of  the  survey  in  this  direction  was  interrupted — an  event 
much  to  be  lamented. 

Yet  a  monograph  can  give  only  what  is  revealed  by  the  de- 
velopments accessible  at  the  time  it  is  written ;  and  since  mining 
continually  makes  new  exposures,  and  for  the  most  part  oblit- 
erates the  old  ones,  a  complete  scientific  inquiry  should  involve 
provision  for  the  repeated  examination  of  a  given  mining  dis- 
trict, and  for  publication,  at  intervals  of,  say,  five  or  ten  years, 
of  the  new  knowledge  thus  acquired. 

It  is  scarcely  to  be  doubted  that  the  investigation  of  the  ge- 
netic relations  of  a  thing  is  necessary  to  complete  our  knowledge 
of  it,  and  that  this  inquiry  is  therefore  obligatory  as  a  part  of 


234  THE    GENESIS    OF    ORE-DEPOSITS. 

the  study  of  anything  which  we  desire  to  know  exhaustively. 
Dr.  Raymond  (discussion  at  the  Virginia  Beach  Meeting,  p.  226) 
has  defended  the  introduction  of  this  principle  into  the  science 
of  ore-deposits,  for  which  I  thank  him  heartily. 

Messrs.  W.  P.  Blake  and  A.  "Winslow  have  controverted  my 
views  concerning  the  original  source  of  the  lead-  and  zinc-de- 
posits of  Missouri  and  Wisconsin,  condemning  at  the  same  time 
the  similar  views  brought  forward  at  the  same  Chicago  meeting 
in  the  paper  of  Dr.  W.  P.  Jenney.  Since  I  am  personally  ac- 
quainted only  through  a  tourist's  journey  with*  the  relations  of 
these  deposits,  which  extend  over  so  large  a  region,  and  am, 
moreover,  not  master  of  the  wide  literature  of  the  subject,  I 
must  leave  the  defence  of  the  principles  asserted  to  Dr.  Jenney, 
and  will  here  simply  refer  to  his  reply,  contained  in  the  present 
discussion. 

With  regard  to  Mr.  Winslow's  observations,  I  must  confess 
that  I  am  acquainted  neither  with  the  mine  at  Doe  Run  nor  with 
the  publications  of  Messrs.  Strong  and  Chamberlin.  But  I  know 
that  concerning  every  region  where  lead-  and  zinc-ores  occur 
in  limestone  and  dolomite,  the  two  opposite  theories  as  to  their 
origin  invariably  appear;  and  that  in  terranes  consisting  of 
structural  plateaux,  with  nearly  undisturbed  position  of  strata, 
the  representatives  of  the  view  that  these  ores  were  deposited 
simultaneously  with  the  country-rock  have  the  great  advantage 
that  the  conditions  of  stratification  are  in  their  favor. 

Besides  the  paper  here  in  discussion,  I  have  lately  devoted 
to  the  deposits  of  lead-  and  zinc-ores  in  soluble  rocks  a  special 
treatise,*  in  which  I  have  compared  the  occurrences  of  such 
deposits  in  plateau-regions  with  the  conditions  obtaining  in 
mountain  regions  with  already  disturbed  stratification.  This 
publication  originated  in  an  address  delivered  b}T  me  at  a  miners' 
congress  in  Klagenfurt,  that  is  to  say,  in  the  center  of  a  mining 
industry  based  upon  mineral  occurrences  of  this  class. 

In  order  to  counteract  a  conception  based  upon  local  condi- 
tions, I  have  placed  side  by  side  the  various  alpine  occurrences 
of  Carinthia  with  those  of  the  plateaux  of  Upper  Silesia  and 
America,  illustrating  them,  according  to  my  custom,  with 


*  "Ueber  die  Entstelmng  der  Blei-und  Zinklagerstatten  in  aufloslichen  Ge- 
steinen."  —  Jahrb.  d.  k.k.  Bergakademien,  1893. 


THE    GENESIS    OF    ORE-DEPOSITS.  235 

drawings  of  the  typical  features.  Among  others,  the  occur- 
rences in  Sardinia  and  in  the  North  of  England  are  discussed, 
and  use  is  made  of  recent  literature  concerning  the  Upper  Sile- 
sian  plateau.  In  this  place,  I  can  only  remark  that  some  of  these 
occurrences  in  the  mountain  terranes  carry  evident  traces  of  the 
subsequent  derivation  of  the  ores  from  below ;  and  that  this  fact 
alone  is  an  argument  for  the  similar  origin  of  the  plateau-de- 
posits, which  so  closely  resemble  the  former  in  all  other  respects. 

The  treatise  I  have  mentioned  does  not  include  the  observa- 
tions made  by  me  in  the  spring  of  the  present  year  upon  the 
analogous  deposits  of  Laurium  in  Greece,  which  are  likewise  in 
a  structural  plateau ;  but  I  can  assure  the  reader  that  the  de- 
velopments of  that  region  also  indicate  the  derivation  of  the 
ores  from  below. 

So  far  as  Mine  la  Motte  is  concerned,  I  can  attach  no  great 
weight  to  the  observations  which  I  made  there,  upon  a  hasty 
journey.  Nevertheless,  the  specimens  of  ore  disseminated  in 
sandy  dolomite  which  I  brought  away  show  distinctly  upon  the 
surfaces,  after  polishing,  the  secondary  intrusion  of  the  ore  into 
the  country-rock. 

With  regard  to  Mr.  T.  A.  Rickard's  criticisms,  I  would  ob- 
serve that  formerly  the  theories  of  ascension,  descension  and 
lateral  secretion  were  generally  spoken  of  without  the  assign- 
ment of  any  cause  for  the  assumed  movements  of  the  subterra- 
neous liquids.  I  think,  however,  that  I  have  secured  some 
definiteness  of  conception  by  showing  the  actual  descent  of  the 
vadose  circulation  and  the  ascent  of  the  deep  circulation,  and 
by  interpolating  the  lateral  movement  between  the  two.  This 
gives  reality  to  the  processes  formerly  conceived  abstractly,  and 
makes  it  possible  to  discuss  them. 

Mr.  Rickard  observes  that,  with  reference  to  the  formation 
of  ore,  I  have  laid  special  emphasis  upon  ascending  mineral  so- 
lutions (p.  191  of  this  volume).  I  meant  to  do  this,  however, 
only  with  regard  to  the  sulphides.  These  certainly  were  not 
produced  from  the  descending  solutions,  which  carry  oxygen 
now,  as  they  unquestionably  did  in  former  geological  periods 
also,  and  which  invariably  decompose  sulphides  wherever  (as  is 
the  case  in  the  vadose  zone)  they  come  into  contact  with  them. 
With  regard  to  the  sense  in  which  I  use  the  terms  ascending  and 
descending,  I  will  say  something  below. 


236  THE    GENESIS    OF    ORE-DEPOSITS. 

Mr.  Rickard  suggests  (loc.  cit.)  that,  since  the  increase  of  pres- 
sure and  temperature  favors  solution,  while  their  decrease 
favors  precipitation,  precipitated  ores  are  to  be  expected  rather 
in  the  shallow  zone ;  and  that  this  might  explain  the  circum- 
stance that  (as  he  helieves)  ores  do  not  continue  in  depth. 
"Without  going  into  the  latter  question  in  detail,  I  would  point 
out  that  the  conceptions  of  shallow  and  deep  are  only  relative, 
and  that  in  my  discussion  I  could  only  have  in  mind  the  con- 
ditions existing  at  the  time  of  the  formation  of  the  ores,  and 
not  at  the  present  time.  What  was  once  shallow  may  now  lie 
very  deep,  and  vice  versa.  In  this  respect,  the  character  of  the 
ores  is,  I  think,  the  decisive  fact.  Oxidized  ores  must  have  be- 
come such  in  a  zone  then  shallow,  and  original  sulphides  must 
have  been  deposited  in  a  zone  then  deep,  and  beyond  the  reach 
of  oxidizing  agencies.  For  the  present,  only  the  extreme  of 
these  processes  can  be  clearly  recognized ;  but  it  is  not  impos- 
sible that  future  studies  in  this  direction  may  distinguish  the 
characteristics  of  the  intervening  stages  of  formation,  such  as 
the  deposits  made  during  lateral  movements  of  the  mineral  so- 
lutions. 

It  would  certainly  be  a  step  backward  to  allow  the  estab- 
lished characters  of  the  two  extremes  to  disappear  under  the 
general  term  "  circulation."  In  my  description  of  the  vadose 
circulation  I  have  pointed  out  that,  notwithstanding  its  course 
at  the  ground-water  level  appears  to  be  almost  horizontal,  and 
notwithstanding  an  actual  ascent  of  the  liquid  may  be  locally 
brought  about  by  siphon-action,  nevertheless  a  decided  pre- 
vailing descent  can  be  proved  for  the  vadose  currents.  The 
terms  "  descending,"  "  ascending  "  and  "  lateral "  are  not  applied 
to  a  portion,  but  to  the  whole  line  of  the  current ;  and  to  its 
cause,  as  both  theoretically  and  empirically  determined.  I 
cannot  admit  that  this  is  "  a  narrow  view  of  the  subject,"  likely 
to  hinder  progress  in  this  branch  of  geology ;  on  the  contrary, 
I  believe  it  expresses  a  series  of  observed  facts,  calculated  to  in- 
crease our  knowledge. 

Mr.  Rickard  seems  to  look  at  every  new  conception  in  this 
department  from  the  sole  standpoint  of  its  immediate  usefulness 
in  mining,  and  not  to  reflect  that  the  scientific  investigator  has 
simply  to  seek  the  truth,  without  regard  to  such  considerations. 
His  criticism  might  have  been  more  favorable  in  some  particu- 


THE    GENESIS    OF    ORE-DEPOSITS.  237 

lars  (e.g.,  Virginia  Beach  Discussion,  p.  219,  with  reference  to 
p.  59  of  my  paper),  if  I  had  taken  pains,  in  many  cases  in  which 
I  was  speaking  of  "  ore-deposits,'''  to  explain  that  under  this 
phrase,  used  for  brevity,  I  was  referring  to  deposits  carrying 
metallic  sulphides. 

Mr.  H.  Y.  Winchell  complained,  at  the  Virginia  Beach 
meeting,  that  under  the  head  of  ore-deposits  the  deposits  of 
iron-ore  are  too  often  either  meagerly  or  not  at  all  considered. 
This  complaint  would  be  well  founded  as  against  a  report  on 
the  mineral  resources  of  a  given  region,  in  which  the  economic 
importance  of  the  deposits  is  a  controlling  element;  but  it  is 
scarcely  just  in  its  application  to  a  paper  like  mine,  which  was 
intended  only  to  give  single  instances  in  illustration  of  certain 
genetic  theories.  The  reason  that  iron-ore  deposits  generally 
receive  comparatively  little  attention  in  genetic  discussion  is, 
I  think,  the  simplicity  of  their  conditions,  the  knoAvledge  of 
which  is  to  some  extent  assumed  to  be  familiar,  so  that  authors 
interest  themselves  much  more  in  the  discussion  of  the  more 
complicated  occurrences,  which  have  rarely,  as  a  rule,  been  cor- 
rectly interpreted. 

I  am  indebted  to  Mr.  Winchell  for  making  good  my  omission 
by  adding  to  my  paper  his  account  of  iron-ore  deposits  known 
to  him.  Since  the  deposits  he  cites  consist  of  oxidized  ores 
only,  they  may  well  have  been  formed  by  an  originally  vadose 
circulation.  I  must,  however,  point  out  that  some  iron-ore  de- 
posits may  be  of  idiogenous  origin.  Thus,  I  consider  the 
oolitic  structure  of  some  deposits  (e.g.,  those  of  hematite  in  the 
Silurian  of  Central  Bohemia)  as  a  sign  of  their  original  depo- 
sition in  the  basin.  I  have  had,  however,  far  too  little  to  do 
with  these  deposits  to  be  able  to  determine  more  closely  the 
significance  of  the  remains  of  brachiopods  (e.g.,  orthis  shells), 
which  occur,  transformed  into  hematite,  together  with  the 
oolites. 

The  iron-ore  beds  of  the  Silurian  basin  of  Bohemia  have  a 
certain  analogy  with  those  of  the  Huronian  basin  of  Michi- 
gan, especially  as  regards  the  length  and  continuity  of  their 
outcrops,  and  their  connection  with  tufas  of  the  eruptive  rocks. 
In  the  latter,  as  is  indicated  by  the  beautiful  pseudomorphs  of 
chlorite  after  garnet,  considerable  metamorphosis  must  have 
taken  place. 


238  THE    GENESIS    OF    ORE-DEPOSITS. 

Concerning  the  Mesabi  iron-ores,  I  am  indebted  to  this  critic 
for  the  illustrations  of  two  specimens  which  he  has  published. 
They,  indeed,  suggest  reflections  as  to  their  probable  genesis, 
upon  which,  however,  I  do  not  trust  myself  to  venture  at  this 
time. 

In  reply  to  Mr.  WinchelPs  criticism  that,  while  laying  un- 
necessary emphasis  upon  the  correctness  of  the  ascension- 
theory,  I  appear  to  concede  to  the  theory  of  lateral  secretion 
not  an  atom  of  truth,  I  beg  to  observe : 

1.  That  I  deem  lateral  secretion,  in  the  sense  in  which  it  is 
defined  by  Professor  Sandberger,  to  be  possible  only  in  the  zone 
above  the  ground-water  level,  and,  therefore,  in  the  formation 
of  oxidized  ores  only,  and  not  for  sulphide-ores. 

2.  That  I  am,  indeed,  obliged  (as  I  have  shown  on  page  28) 
to  assume  a  lateral  movement  of  liquids  in  the  deep  zone.   But 
this  is  a  region  in  which  present  processes  cannot  be  directly 
observed,  and,  therefore,  no  clues  to  the  conditions  of  deposi- 
tion are  found.     Hence,  I  was  not  able  to  describe  such  con- 
ditions in  my  paper.     It  is  possible  tha.t,  in  the  course  of  time, 
conditions  of  deposition  may  be  discovered  which  can  best  be 
explained  in  this  way.     I  have  not  yet  encountered  such  a 
case. 

The  same  is  true  as  to  regions  in  which  the  two  extreme 
branches  of  the  subterranean  circulation  take  on  a  lateral 
course.  The  case  supposed  by  Mr.  Winchell,  in  which  a  de- 
posit can  be  ascribed  to  ascension  and  also  to  lateral  secretion, 
I  do  not  clearly  understand,  since  a  physically  weaker  current 
is  not  capable  of  displacing  a  stronger  one.  While  the  extreme 
forms  of  circulation — that  is,  both  the  ascending  and  descend- 
ing branches — possess  a  pronounced  character,  it  must  be  ex- 
pected that  the  character  of  the  branches  connecting  these  ex- 
tremes will  be  less  distinct. 

Mr.  John  A.  Church  does  not  agree  with  me  regarding  ore- 
deposits  in  open  spaces  as  a  very  frequent  phenomenon,  and  ex- 
presses the  opinion  that  open  spaces  cannot  exist  at  great  depths 
(such  as  3  to  5  kilometers).  I  must  remind  him  that  in  order 
to  establish  the  first  proposition  the  most  important  observa- 
tions of  a  great  number  of  observers  for  more  than  a  century 
must  be  disproved.  He  cannot  have  failed  to  notice  that  ore- 
deposits  of  that  form  which  has  been  relatively  most  thor- 


THE    GENESIS    OF    ORE-DEPOSITS.  239 

oughly  studied,  namely,  fissure-veins,  consist  predominantly  of 
separate  crusts,  often  marvellously  distinct,  covering  what  were 
once  the  walls  of  the  fissure-space.  Even  if  his  proposition  be 
confined  to  deposits  of  great  thickness  and  extent  in  depth, 
which  are  deemed  to  have  been  formed  (as,  for  instance,  the 
Comstock  lode,  which  he  has  studied)  by  substitution,  replace- 
ment or  metasomasis,  he  cannot  possibly  deny  the  existence  of 
other  thick  and  deep  deposits,  the  structure  of  the  ores  of 
which  evidently  represents  the  filling  of  open  spaces.  For  in- 
stance, some  of  the  Przibram  veins,  which  have  been  worked 
to  the  depth  of  more  than  1100  meters,  and  the  ore  of  which 
often  exceeds  10  meters  in  thickness,  must  certainly  be  reck- 
oned as  wide  and  deep ;  yet  the  ores  from  their  deepest  por- 
tions do  not  differ  in  the  least,  so  far  as  structure  is  concerned, 
from  those  which  occur  in  the  shallower  parts.  Both  regions 
present  fragments  of  the  country-rock  of  all  sizes,  surrounded 
by  the  vein-material.  Moreover,  these  fragments  surrounded 
by  quartz  usually  predominate  in  one  or  the  other  of  the  crusts 
of  the  vein-filling. 

Mr.  Church  seems  to  allow  small  value  to  the  observations 
which  it  is  possible  to  make  upon  the  ores  themselves  and  the 
adjoining  country-rock.  This  is  equivalent  to  the  rejection  of 
the  only  means  of  obtaining  data  concerning  their  probable 
genesis.  It  is  difficult  to  discuss  such  an  objection,' particularly 
in  its  bearing  upon  the  phenomenon  of  crustification,  which  I 
consider  one  of  the  most  important  genetic  factors,  and  con- 
cerning which  I  will  speak  further  in  connection  with  my  reply 
to  other  critics. 

Mr.  Church  declares  the  Comstock  vein-mass  to.be  the  prod- 
uct of  substitution — that  is,  of  metasomatic  alteration  —  and 
denies  entirely  that  it  is  a  fissure-vein.  He  says  I  have  mis- 
understood him  in  saying  (p.  92  of  this  volume)  that  he  found 
crusts  of  quartz,  alternating  with  calcite,  in  the  Justice  mine. 
The  passage  to  which  I  referred  was  the  following:* 

"The  ore  of  the  Justice  is  not  quartz  but  calcite,  with  but  an  insignificant 
amount  of  silica,  and  it  is  noteworthy  to  find  these  two  components  of  the 
lode  dispersed  in  that  banded  arrangement,  which  is  another  of  the  accepted 
proofs  of  a  true  fissure-vein.  The  quartz  is  always  on  the  propylite  and  the  cal- 

*  The  Comstock  Lode,  etc.,  by  John  A.  Church,  New  York,  1870,  p.  173. 


240  THE    GENESIS    OF    ORE-DEPOSITS. 

cite  on  the  quartz  ;  but  there  is  no  comparison  in  respect  to  quantity.  The  quartz 
is  always  insignificant  in  thickness,  never  reaching  a  layer  more  than  an  inch  or 
two,  so  far  as  noticed,  except  in  the  dyke-vein,  while  the  calcite  forms  masses 
which  are  several  yards  in  thickness,"  etc. 

Why  is  this  not  what  I  call  crustification  ?  It  is  certainly 
conceivable  that  the  Comstock  was  formed  by  the  opening  of  a 
space  of  discission  at  the  contact  of  diorite  and  diabase,  the 
filling  of  this  space  by  the  deposition  of  silica  and  carbonate 
of  lime  from  solutions,  and  the  repetition  of  these  processes 
until  the  deposit  had  attained  its  present  thickness.  There  is, 
for  example,  in  the  collection  of  the  University  of  Vienna,  a 
large  slab  from  the  Adalbert  vein  at  Przibram,  showing  a  series 
of  thin  galena-veinlets,  the  crystals  of  which  meet  in  the  axis  of 
each  several  veinlet,  showing  that  each  was  separately  filled, 
and  hence  that  the  process  of  opening  and  filling,  regarded  with 
reference  to  the  Adalbert  vein  as  a  whole,  was  repeated  many 
times,  until  the  aggregate  thickness  of  about  one  meter,  shown 
by  this  slab,  had  been  attained.  The  Comstock  might  have 
been  formed  likewise  by  repeated  opening  and  filling,  only  the 
several  fillings  would  have  to  be  thicker,  and  (since  the  material 
varied  little)  the  result  might  be  too  indistinct  to  attract  the  at- 
tention of  the  miner. 

Mr.  Church  regards  the  ore-body  of  the  Justice  mine  as  a 
deposit  separate  from  the  Comstock ;  but  it  is,  nevertheless,  a 
branch  of  the  Comstock  lode,  and  certainly  has  an  analogous 
origin.*  The  occurrence  of  a  crustified  portion,  which  I  think 
the  text  of  Mr.  Church's  description  indicates,  possesses,  there- 
fore, significance  for  both  branches  of  the  Comstock. 

By  crustification,  however,  I  do  not  mean  merely  a  "  banded 
structure."  This  may  indeed  originate,  as  Mr.  Church  says,  in 
various  ways,  but  crustification  cannot;  for  true  crusts  are 
predominantly  chemical  precipitates,  the  crystal-aggregates  of 
which  present  a  certain  arrangement.  For  instance,  the  quartz- 
crystals  usually  stand  perpendicular  to  the  former  cavity-wall, 
directing  their  pyramidal  surfaces  towards  the  central  druse. 
Incrusted  fragments  exhibit  the  same  crusts  as  the  cavity-walls, 
which  is,  at  the  same  time,  an  additional  proof  of  the  existence 
of  an  open  space,  etc.  It  is  true,  that  among  these  chemical 

*  See  Becker's  Geology  of  the  Comstock  Lode,  p.  30. 


THE    GENESIS    OF    ORE-DEPOSITS.  241 

precipitates  there  sometimes  occur  mechanical  sediments,  such 
as  frictional  detritus,  which  may  be  enveloped  by  one  or  another 
of  the  crust-substances ;  but  this  is  by  no  means  a  case  under 
Mr.  Church's  statement  (p.  198  of  this  volume) : 

"Certainly,  a  banded  structure  can  arise  from  the  replacement  of  fragments  ar- 
ranged in  layers  by  pressure  and  friction,  as  well  as  in  many  other  ways,  and  does 
not  prove  deposition  in  a  cavity,  whether  filled  by  water  or  air." 

Pressure  and  friction  can  give  rise  to  no  arrangement  of 
xenogenites  in  separate  crusts;  in  other  words,  no  crustified 
quartz  and  calcite  filling,  such  as  I  suppose  to  exist  in  the  Corn- 
stock.  I  possess,  for  example,  besides  the  ores  from  the  Con- 
solidated Virginia  bonanza,  mentioned  in  my  paper  (page  92), 
some  quartz  specimens  from  the  1500-foot  level  of  the  Belcher 
mine,  in  which  separate  dark  ore-bearing  zones  may  be  distin- 
guished, running  parallel  with  each  other,  even  to  the  repetition 
of  minute  undulations.  This  is,  I  confess,  not  such  a  convin- 
cing case  as  that  of  the  specimen  shown  in  Fig.  53  of  my  paper, 
which  exhibits  numerous  successive  crusts  of  baryte,  fluorite, 
etc.,  no  thicker  than  paper;  or  those  of  the  Raibl  specimens, 
which  consist  of  thousands  of  thin  layers  of  zinc-blende  (whence 
the  name  Schalenblende) ;  but  it  indicates,  at  least,  the  probabil- 
ity of  a  similar  origin.  It  is,  of  course,  not  in  every  ore-deposit 
that  such  incontrovertible  proofs  as  those  last  mentioned  are 
found  and  preserved  for  science. 

Mr.  Church  points  out  (pages  196  and  197  of  this  volume) 
that  metasomatic  processes  effected  in  limestones  through  the 
expulsion  of  the  carbonic  acid  by  a  stronger  acid,  may  also  ex- 
plain the  exhalations  of  carbonic  acid  so  frequent  in  certain 
localities.  I  much  prefer,  however,  to  avoid  the  adoption  of 
such  a  purely  speculative  standpoint,  and  would  only  suggest 
that,  upon  that  view,  the  enormous  volume  of  such  exhalations 
in  volcanic  regions  would  require  us  to  conclude  that  in  those 
regions  immense  masses  of  limestone  are  undergoing  the  met- 
asomatic process  referred  to. 

As  regards,  finally,  the  subsequent  alteration  of  the  original 
ore-deposit,  which,  according  to  Mr.  Church,  partially  passes 
into  hysteromorphism,  it  is  undoubtedly  true  that  mineralo- 
gists, devoted  to  the  study  of  pseudomorphs,  have  collected 
already  valuable  data  in  this  field ;  yet,  I  think,  prolonged  in- 


242  THE    GENESIS    OF   ORE-DEPOSITS. 

vestigation  will  still  be  required  before  general  deductions  can 
be  profitably  discussed. 

Mr.  S.  F.  Emmons,  whom  I  have  to  thank  warmly  for  his 
favorable  judgment  upon  several  portions  of  my  paper,  natu- 
rally does  not  concur  in  the  views  I  have  expressed  concerning 
Prof.  Sandberger's  lateral-secretion  theory,  to  which  he  was 
himself  at  one  time  more  or  less  committed. 

He  objects,  for  instance,  to  my  reference  to  the  barysphere. 
This  is  a  part  of  my  conception  of  our  planet  as  consisting  out- 
wardly of  several  successive,  and  more  or  less  connected,  spher- 
ical envelopes — atmosphere,  hydrosphere,  biosphere,  litho- 
sphere,  and  barysphere — of  which  only  the  exterior  ones  are 
open  to  our  direct  observation.  In  discussing  the  mutual  re- 
actions of  these  great  geological  factors,  which  we  may  briefly 
call  aggregate-spheres,  it  is  unavoidably  necessary  to  refer  to 
the  barysphere,  which  is  beyond  our  observation :  and,  accord- 
ing to  my  habit,  I  have  used  this  term  in  speaking  of  the  source 
of  the  heavy  metals.  It  is  true,  the  term  is  only  a  device  to 
avoid  questions  still  unsolved ;  but  the  same  may  be  said  con- 
cerning the  phrases  "  unknown  depths,"  or  "  unknown  sources 
in  depth,"  which  have  a  similar  meaning. 

It  seems  to  me  that  Mr.  Emmons  and  others  of  my  critics 
have  not  correctly  understood  my  statements  concerning  the 
several  branches  of  the  underground  circulation ;  and  I  there- 
fore beg  permission  to  make  my  meaning  clearer,  even  at  the 
cost  of  a  little  repetition.  For  this  purpose  I  will  take  for  illus- 
tration, not  an  ideal  case,  but  conditions  actually  existing, 
namely,  those  developed  at  Przibram,  concerning  which  there 
exists  an  abundant  literature,  shortly  to  be  increased  (in  the 
second  volume  of  my  Archiv  fiir  praktische  Geologic)  by  a  mon- 
ograph of  my  own. 

The  Przibram  district  lies,  in  round  numbers,  about  500  me- 
ters above  sea-level,  and  the  mine-workings  extend,  as  is  well 
known,  to  more  than  that  distance  below  sea-level.  The 
ground-water  level  is  but  a  few  meters  under  the  surface.  The 
deepest  adit  drains  the  mines  to  about  100  meters;  and  every- 
thing below  that  level  is  strictly  deep  workings,  from  which  the 
water  is  lifted  to  the  adit-horizon.  A  comparison  of  the  water 
raised  from  different  levels  shows  that  the  largest  quantities 
come  from  the  upper  ones,  and  that  the  amounts  diminish  with 


THE    GENESIS    OF    ORE-DEPOSITS.  243. 

increasing  depth,  so  that  at  about  300  meters  below  sea-level  no 
water  remains  to  be  raised,  the  ruling  rock-  and  air-tempera- 
ture of  about  23°  C.  (74°  F.)  at  that  depth  sufficing  to  evap- 
orate the  small  existing  quantity  of  water.  This  is  certainly  a 
striking  proof  that  the  water  encountered  in  mining  is  of  at- 
mospheric origin. 

The  ore-deposits  are  steeply-dipping  fissure-veins,  which  are 
mined  by  reason  of  their  richness  in  silver  (about  5  per  cent., 
or  50  kilos  per  metric  ton — or  say  1458  ounces  Troy  per  ton  of 
2000  pounds  avoirdupois).  Even  in  the  neighborhood  of  the 
surface  the  sulphides  predominated,  but  were  mixed  with  a 
great  variety  of  beautiful  minerals,  which  have  made  Przibram 
famous  among  collectors,  and  most  of  which,  according  to  the 
results  of  the  investigations  of  F.  A.  Reuss  and  others,  are  of 
secondary  origin.  It  cannot  well  be  doubted  that  this  altera- 
tion is  due  to  the  oxidizing  properties  of  the  liquids  coming 
from  the  surface.  But  this  variety  of  minerals  is  confined  at 
Przibram  to  the  upper  zones.  Since  mining  has  penetrated  to 
lower  levels,  its  product  has  been  mainly  only  rich  argentifer- 
ous galena,  with  accompanying  zinc-blende,  etc.  The  diminu- 
tion in  secondary  minerals,  so  far  as  it  can  be  determined, 
seems  to  follow  closely  the  progressive  diminution,  in  depth, 
of  the  quantity  of  surface-waters. 

Concerning  the  origin  of  the  secondary  alterations,  there  is 
(as  Mr.  Church  may  be  pleased  to  know)  no  doubt  at  Przibram. 
The  only  question  at  issue  concerns  the  explanation  of  the  orig- 
inal vein-filling,  consisting  of  sulphides.  This  must  have  come, 
of  course,  from  some  rock  as  a  source ;  and  on  this  point  views 
are  at  variance. 

1.  Professor  Sandberger  at  first  conceived  that  this  filling 
came  directly  from  the  country-rock  (Nebengestdri).     The  tech- 
nical term  Nebengestein  is  more  definite,  perhaps,  than  "  country- 
rock."     It  means  literally  the  rock  alongside,  or  the  country- 
rock  or  wall-rock  immediately  in  contact  with  the  deposit.     In 
this  sense,  it  is  impossible  to  conceive  of  any  other  process  than 
that  of  lateral  secretion,  which  could  make  the  Nebengestein  the 
source  of  the  filling;  and  I  have  attempted  in  my  paper  to 
show  the  improbability  of  such  a  lateral  secretion  of  such  a 
filling. 

2.  Mr.  Emmons,  in  his  paper  on  "  The  Geological  Distribu- 

16 


244  THE    GENESIS    OF    ORE-DEPOSITS. 

tion  of  the  Useful  Metals  in  the  United  States,"  read  at  the 
Chicago  meeting  (Trans.,  xxii.,  53),  has  connected  the  deriva- 
tion of  the  various  metals  of  different  deposits  with  the  observed 
geological  conditions  of  that  country,  discussing  the  metals, 
iron,  manganese,  nickel,  tin,  copper,  lead  and  zinc,  mercury  and 
gold  and  silver  separately.  In  his  criticism  of  my  views  in  this 
field  (pages  200  and  201  of  this  volume),  he  has  taken  occasion 
to  express  a  general  statement  for  all  ore-deposition.  Accord- 
ing to  his  opinion,  the  metallic  constituents  were  derived  by 
lateral  secretion  from  rocks  within  "  reasonable  proximity;" 
and  "  ore-bearing  currents  may  in  such  cases  have  had  an  up- 
ward, downward  or  lateral  motion,  according  to  differing  local 
conditions  of  rock-structure."  This  latter  expression  I  would 
like  to  amend  in  accordance  with  the  fact  that,  while  the  local 
conditions  of  rock-structure  indeed  influence  the  movements  of 
liquids,  the  true  causes  of  the  upward,  downward  and  lateral 
motion,  as  explained  in  my  discussion  of  this  point,  lie  outside 
the  particular  rock-structure. 

I  would  invite  Mr.  Emmons  to  take  the  standpoint  sketched 
on  pages  55  and  56  of  this  volume,  in  the  depths  of  the  Przi- 
bram  mines,  and  see  how  he  would  get  along  with  his  assump- 
tion of  lateral  movement.  And  I  must  repeat  that  it  is  not  so 
much  the  local  direction  of  the  currents  as  the  general  char- 
acter and  cause  of  the  flow  which  should  be  kept  in  view. 

The  general  phenomenon  of  descending  currents  in  the  Przi- 
bram  mines  is  clearly  subsequent  to  the  formation  of  the  ore- 
deposits  ;  and  the  existence  of  lateral  movements  of  the  vadose 
circulation  which  could  form  these  deposits  is  inconceivable. 
Let  us  see,  then,  whether  such  movements  could  occur  in  depth, 
in  the  sense  defined  by  me  on  page  28  of  this  volume,  and 
quoted  by  Mr.  Emmons. 

We  should  be  forced  to  assume  that  the  open  vein-channels 
had  not  extended  much  deeper  than  the  point  (500  to  700  me- 
ters below  sea-level)  at  which  I  have  invited  Mr.  Emmons  to 
stand,  and  also  that  there  was  no  special  upward  tendency  of 
the  waters  filling  these  channels.  A  lateral  continuous  move- 
ment would  be  only  possible  if  there  was  something  "  in  reason- 
able proximity  "  which  would  consume  the  moving  current,  or 
force  it  back  to  the  surface.  To  expect  this  phenomenon  in  a 
terrane  already  traversed  by  channels  reaching  to  the  surface  is 


THE    GENESIS    OF    ORE-DEPOSITS.  245 

irrational.  In  the  only  conceivable  sense,  it  would  merely 
make  the  lateral  movement  an  incidental  part  of  a  general  up- 
ward circulation.  But  this  favors  my  view  of  the  ascent  of  min- 
eral solutions  from  greater  depths  than  have  yet  been  reached 
in  mining,  i.e.,  from  "  unknown  depth,"  as  Mr.  Emmons  ex- 
presses it,  or  from  the  barysphere,  as  I  have  expressed  it.  He 
also,  by  the  way,  assumes  the  origin  of  the  heavy  metals  from 
the  barysphere  (or  "  from  the  depths,"  as  he  prefers  to  say), 
and  goes  so  far  as  to  intimate  that  I  would  make  the  theory 
more  plausible  by  allying  it  with  that  of  Vogt,  according  to 
which  a  process  of  so-called  differentiation,  during  the  cooling 
of  the  eruptive  rocks,  has  concentrated  their  metallic  contents 
in  certain  regions  more  or  less  accessible  to  our  observation. 
For  my  part,  I  must  wait  until  Vogt's  ideas  have  assumed  a 
more  solid  form ;  but  I  cannot  help  suspecting  that  Mr.  Em- 
mons favors  them  principally  because  they  bring  the  concen- 
trated metals  in  eruptive  rocks  within  the  reach  of  lateral  secre- 
tion, as  a  forming  process  for  ore-deposits. 

Mr.  Emmons  doubts  my  conclusion,  based  upon  Noggerath's 
observations,  that  waters  rising  under  pressure  are  capable  of 
creating  a  channel  for  themselves  in  soluble  rocks.  In  this 
connection  I  must  refer  to  the  difficulty  encountered  in  explain- 
ing the  cavities  containing  pipes  of  ore  in  soluble  rocks.  In 
my  monograph  on  Resbanya,*  published  when  Noggerath's 
work  was  unknown  to  me,  I  was  forced  to  assume,  as  the  cause 
of  the  formation  of  the  cavity,  the  downward  vadose  currents, 
and  as  the  cause  of  the  filling,  on  the  other  hand,  the  ascend- 
ing currents  of  the  deep  circulation ;  in  other  words,  two  pro- 
cesses, representing  the  extremes  of  circulation,  and  succes- 
sively acting  along  the  same  line.  Such  a  dilemma  may  be 
presented  by  any  ore-deposit  in  limestone.  Indeed,  I  became 
acquainted  subsequently  with  instances  indicating  that  the  two 
processes  of  cavity-forming  and  cavity-filling  may  have  been 
sometimes  almost  simultaneous,  f  I  was  greatly  pleased  when 
I  learned  of  RToggerath's  observations  and  deductions,  and  I 

*  Geologisch-montanistische  Studie  der  Erdagerstdtten  von  Rezbdnya,  in  S.  Ungarn. 
Published  by  the  Hungarian  Geol.  Soc.,  Budapest,  1874. 

t  See  my  paper  in  Jahrb.  der  k.  k.  Bergakad.,  1893,  p.  18,  "Ueber  die  Ensteh- 
ung  der  Blei-  und  Zinklagerstiitten  in  aufloslichen  Gesteinen,"  especially  Fig. 
14,  pi.  iii. 


246  THE    GENESIS    OF    ORE-DEPOSITS. 

took  pains  at  that  time  to  acquaint  Mr.  Emmons  by  letter  with 
the  consequent  change  in  my  own  views.  The  observation,  as 
I  convinced  myself  in  1885,  cannot  now  be  verified,  for  the 
whole  place  at  Burtscheid  is  completely  built  over;  but  ~N'6g- 
gerath  was  a  highly  conscientious  observer,  and  there  can  be 
no  doubt  of  the  correctness  of  his  statement  of  the  facts. 
Moreover,  the  phenomenon  is,  a  priori,  inevitable.  If  the  highly 
dilute  currents  of  the  vadose  circulation,  descending  by  gravity, 
can  eat  out  their  own  channels  in  salt  or  limestone  (as  is  shown 
at  p.  21  and  other  places  in  my  paper),  all  the  more  might  such 
effects  be  expected  from  waters  ascending  under  pressure  and 
more  highly  charged  with  reagents.  Fig.  9  of  my  paper,  show- 
ing the  wedge-shaped  spaces  of  corrosion  described  by  Daubree 
from  Bourbonne-les-Bains,  with  their  summits  directed  upward, 
gives  actual  proof  of  this. 

My  reference  to  the  wedge-like  form  of  certain  deposits  at 
Laurium  \vas  based  on  an  ideal  profile.  In  the  spring  of  the 
present  year  (1894)  I  personally  visited  the  district,  and  strove 
to  secure  more  accurate  drawings  of  the  position  and  form  of 
the  deposits.  I  must  confess  that  I  was  not  able  to  find  any 
such  drawings,  and  I  must  therefore  submit  to  the  rebuke  of 
Mr.  Emmons.  So  far  as  I  know  the  literature  concerning  the 
Larium  district,  the  only  accurate  drawings  are  those  of  the 
French  company  in  the  treatise  of  A.  Cambresy.*  (I  take  this 
opportunity  to  correct  a  typographical  error  in  the  pamphlet 
edition  of  my  paper.  Fig.  87  was  taken,  not  from  Cordelia 
but  from  liuot.) 

With  regard  to  the  essential  difference  of  opinion  concerning 
the  Leadville  deposits,  I  may  observe  that  the  reason  I  ventured 
to  discuss  that  district  without  having  personally  studied  it  is 
to  be  found  in  the  magnificent  monograph  of  Mr.  Emmons,  the 
interesting  conditions  which  it  describes,  and  its  contradiction 
of  current  views  as  to  the  origin  of  the  Leadville  ores.  Pass- 
ing by  all  corrections  and  criticisms  on  points  of  minor  im- 
portance, I  wish  only  to  keep  in  view  this  essential  difference 
of  opinion,  and  to  inquire  what  were  the  convincing  reasons 
which  lead  Mr.  Emmons  to  assert  in  this  case  a  descent  of  the 
mineral  solutions. 

*  "  Le  Laurium,"  par  A.  Cambresy,  Rev.  Univ.  des  Mines,  3  ser.,  t.  vi.,  1889. 


THE    GENESIS    OF    ORE-DEPOSITS.  247 

He  separates  the  sources  of  the  metallic  substances  into  "im- 
mediate "  and  "  ultimate."  The  latter,  by  reason  of  their  purely 
speculative  nature,  he  does  not  discuss,  but  devotes  himself  to 
the  former.  Without  being  able  to  doubt  that  these  substances 
originally  came  from  great  depths,  and  without  being  willing  to 
assert  that  they  came  wholly  from  the  country-rock  actually 
adjoining  the  deposits,  he  believes  : 

1.  That  they  came  from  above. 

2.  That  they  were  derived  chiefly  from  neighboring  rocks. 
With  regard  to  the  first  of  these  propositions,  I  can  find  in 

his  elaborate  monograph  no  tangible  proofs  whatever,  only  con- 
clusions deduced  from  certain  observations.  The  shape  and 
position  of  the  ore-deposits,  whether  of  those  at  the  contact 
between  porphyry  and  lime,  or  those  in  the  limestone,  afford 
no  conclusive  proof  of  descending  mineral  solutions  as  their 
source.  Indeed,  this  is  disproved  by  the  fact  that  the  deposits 
were  originally  sulphides  (as  they  are  now  shown  still  to  be  at 
greater  depths),  and  such  sulphide-deposits  cannot  be  asserted 
to  have  been  formed  by  solutions  descending  from  the  surface 
(unless  such  an  application  should  be  made  of  the  case  cited  on 
p.  107  of  my  paper,  namely,  the  reduction  to  sulphides  by  means 
of  organic  matter).  "  The  interior  structure  of  the  deposits  and 
of  the  country-rock,  so  far  as  they  are  described  in  the  publica- 
tions on  the  subject,  likewise  fail  to  furnish  any  conclusive 
proof  of  this  assumption. 

In  his  re-examination  of  the  mines  in  1890,  Mr.  Emmons 
found,  even  in  the  original,  unaltered  sulphide-ores,  no  crustifi- 
cation,  from  which  he  concludes  that  in  this  case  there  has  been 
no  deposition  of  ore  in  open  spaces,  but  a  metasomatic  replace- 
ment of  the  limestone.  It  is  to  be  hoped  that  investigations 
on  this  point  will  not  be  wholly  abandoned  in  future.  Mr.  Em- 
mons mentions  also  his  recognition  of  the  granular  structure, 
joints  and  cleavage  of  the  original  limestone  in  the  sulphide- 
ores  of  the  A.  Y.  and  Minnie  mines,  and  speaks  of  the  cracks 
in  the  top  of  the  ore-body,  "  through  which  the  ore-bearing 
solutions  had  descended."  This  is  clearly,  as  stated  in  this 
form,  an  expression  of  opinion.  A  detailed  and  purely  objec- 
tive description,  particularly  if  accompanied  with  drawings, 
would  be  highly  valuable,  and  might  constitute  the  tangible 
proof,  the  absence  of  which  I  have  pointed  out.  Mr.  Emmons 


248  THE    GENESIS    OF    ORE-DEPOSITS. 

gives  us  ground  to  hope  for  further  observations  in  this  direc- 
tion, based  upon  the  latest  developments  of  the  mines.  For  the 
present,  however,  it  cannot  he  said  that  we  have  any  decisive 
proof  from  the  interior  structure  of  these  deposits. 

The  facts  described  in  the  literature  concerning  Leadville 
may  be  equally  well  used  in  support  of  the  ascension-theory. 
As  I  have  remarked  (page  107  of  this  volume),  the  ores  were  at 
first  conceived  to  occur  at  the  contact  between  porphyry  and 
limestone,  or  confined  to  the  lime ;  but  afterwards  it  became 
clear  that  not  the  whole  contact-surface  as  such,  but  only  cer- 
tain zones  of  it,  could  be  regarded  as  the  principal  centers  of 
the  accumulation  of  ore.  These  ore-shoots,  lying  in  and  near  the 
contact-plane,  were  the  channels  of  which  the  mineral  solutions 
availed  themselves.  A  parallel  is  thus  furnished  to  various 
other  ore-deposits ;  for  instance,  the  zinc-  and  lead-deposits  of 
the  Alps,  the  shoots  of  which  are  near  a  contact  of  soluble  with 
insoluble  rock,  and  pursue  the  same  direction  as  the  stratifica- 
tion.* For  the  establishment  of  this  analogy,  credit  is  due  to 
the  mining  engineers  who  have  published  their  observations  at 
Leadville,  and,  as  Mr.  Emmons  implies, f  have  rendered  val- 
uable assistance  in  enlarging  our  knowledge  of  the  facts  as  de- 
veloped by  mining. 

The  text  of  Mr.  Emmons's  great  monograph  on  Leadville 
shows  plainly  (p.  572)  that,  under  the  impression  produced  by 
the  first  publication  of  Professor  Sandberger,  the  author  deemed 
the  ascension-theory  to  have  been  already  completely  over- 
thrown. He  assumes  that  the  type  of  a  vein,  as  described  by 
earlier  authorities,  is  a  purely  ideal  conception,  and  does  not 
exist  in  nature.  To  show  that  these  writers  had  before  them, 
on  the  contrary,  a  real  condition,  I  have  cited  the  developments 
at  Przibram.  If  we  substitute,  in  that  case,  for  the  space  of 
discission  the  spaces  occupied  by  the  Leadville  deposits,  the 
situation,  as  concerns  the  question  of  the  direction  of  the  ore- 
bearing  circulation,  is  not  altered.  The  flat  dip  of  the  ore- 
shoots  and  the  solubility  of  the  country-rock  at  Leadville  are 
scarcely  decisive  as  to  this  question.  Nor  does  the  depth  thus 

*  See  my  treatise  (1893),  already  cited,  on  the  "Origin  of  Lead-  and  Zinc-De- 
posits in  Soluble  Kocks." 

f  Page  202  of  this  volume.  See  also  "  The  Mining  Work  of  the  U.  S.  Geol. 
Survey,"  Trans.,  x.,  412  et  seq. 


THE    GENESIS    OF    ORE-DEPOSITS.  249 

far  attained  in  Leadville  mining  afford  conclusive  evidence.  In 
my  judgment,  therefore,  notwithstanding  the  differences  be- 
tween Przibram  and  Leadville,  the  same  inference  must  be 
drawn  in  both  cases  as  to  the  direction  of  the  ore-bearing  cir- 
culation. In  other  words,  Leadville  must  be  declared  to  be  no 
exception  to  the  general  rule  that  ore-deposits  carrying  metallic 
sulphides  have  been  formed  by  ascending  solutions. 

Whether  the  metallic  contents  were  derived  wholly  or  pre- 
dominantly from  the  eruptive  rocks  adjacent  to  the  deposits  or 
occurring  within  a  certain  distance,  is  an  independent  question. 

Mr.  G.  F.  Becker's  criticism  (page  204  of  this  volume),  hav- 
ing been  prepared  without  opportunity  for  a  thorough  combina- 
tion of  authorities,  is  considered  as  preliminary  only.  It  deals, 
as  does  that  of  Mr.  Emmons,  in  the  main,  with  metasomatic 
formations,  without  reference  to  formations  in  open  spaces,  and, 
contemplating  the  former  exclusively,  seems  to  disparage  the 
emphasis  which  I  have  laid  upon  crustification  as  a  clear  proof 
of  the  filling  of  open  spaces.  According  to  his  view,  the  recog- 
nizability  of  successive  deposits  is  dependent  upon  incidental 
local  circumstances,  but  the  instances  he  gives  do  not  appear 
to  me  adapted  to  prove  his  proposition  that  crustification  may 
be  produced  by  other  causes  than  that  which  I  have  assigned. 

The  banded  structure  of  agates,  so  far  as  I  have  had  oppor- 
tunity to  study  it,  is  a  genuine  crustification.  It  exhibits  in- 
crusted  nuclei,  stalactites,  and  other  formations  characteristic 
of  deposition  in  an  open  space,  quite  independently  of  the 
question  whether  changes  in  concentration  or  rapidity  of  cir- 
culation or  in  the  substances  contained  in  the  solution  were  the 
occasion  of  precipitation.  In  like  manner  the  precipitate  formed 
upon  a  piece  of  iron  immersed  in  a  solution  of  copper  sulphate 
is  a  genuine  crust,  the  iron  serving  as  the  cause  of  the  precipi- 
tation ;  and  the  circumstances  of  such  a  precipitation  in  a  space 
filled  with  solution,  though  the  process  take  place  above  ground, 
present  some  analogies  with  underground  conditions. 

A  party  of  mine-thieves  once  entered  by  night  an  old  and  ex- 
tensive mine  in  Transylvania  for  the  purpose  of  blasting  off  and 
carrying  away  an  exposed  mass  of  gold-ore.  The  shot  opened 
a  hole  into  an  old  working  (coranda,  in  the  Roumanian  lan- 
guage), and  one  of  the  miners  crawled  through.  The  immen- 
sity of  the  space  in  which  he  found  himself  astonished  him 


250  THE    GENESIS    OF    ORE-DEPOSITS. 

greatly,  but  his  exclamations  of  wonder  were  cut  short  by  the 
crowing  of  a  cock,  which  revealed  to  him  that  he  stood  under 
the  night  sky,  in  a  great  surfacQ-coranda  or  open  quarry,  which 
covered  the  whole  area  of  the  mine.  Under  some  circumstances, 
therefore,  it  is  clear  that  underground  and  above-ground  are 
not  so  very  far  apart ! 

A  mineral  solution  standing  in  a  laboratory-beaker,  exposed 
to  the  air,  may  practically  represent,  from  our  standpoint,  a 
subterranean  space,  the  lower  part  of  which  is  filled  with  liquid 
and  the  upper  part  with  gas,  as  I  conceived  it  on  p.  24  of  my 
paper. 

Mr.  Becker  doubtless  means,  by  the  example  he  cites,  to 
argue  that  the  banded  structure  may  originate  also  through  re- 
placement of  the  idiogenites  by  xenogenites.  This  may  be  true, 
but  his  instances  do  not  support  the  hypothesis ;  for  the  pseudo- 
morphosis  of  galena  after  calcite  is  not  a  replacement  of  lime- 
stone by  galena.  Moreover,  not  every  "  banded  structure  "  is  a 
crustification. 

Mr.  Becker  names  two  sorts  of  indications  of  replacement, 
namely,  crystalline  pseudomorphism  and  the  irregular  enlarge- 
ment of  fissures  in  the  replaced  mass.  I  beg  to  say  that  on 
pp.  15  and  16  of  my  paper  I  have  mentioned  several  other 
signs,  such  as  the  retention  of  the  structure  of  the  original 
mass ;  the  transformation  of  fossils  into  ore ;  the  occurrence  of 
remaining  nuclei  of  the  original  rock,  etc.,  and  that  I  also  sup- 
pose a  metasomatic  process  to  have  taken  place  when  the  evi- 
dence is  merely  negative,  that  is,  where  indications  of  cavity- 
formation,  in  other  words,  crustification,  are  absent.  But  I  have 
found  deposits  where  the  indications  of  both  processes  occur 
side  by  side,  as,  for  instance,  at  Rodna,  in  Transylvania.  It 
was  at  this  place  that  I  had  the  opportunity,  thirty  years  ago, 
to  demonstrate  the  metasomatic  origin  of  an  ore-deposit.  Since 
that  time,  however,  I  have  never  visited  the  locality,  and  have 
received  only  superficial  data  concerning  further  developments. 
Outside  of  calamine-deposits,  I  have  not  encountered,  in  my 
later  explorations  any  cases  of  metasomatic  formation;  and  I 
have  been  led  to  attach  ever-increasing  importance  to  the  de- 
posits formed  in  open  spaces,  the  list  of  which,  as  known  to  me, 
has  been  continually  growing,  while  their  definite  characteristics 
have  become  more  and  more  unmistakably  clear.  Any  differ- 


THE    GENESIS    OF    ORE-DEPOSITS.  251 

ence  of  opinion  which  has  arisen,  as  a  consequence,  between 
my  American  colleagues  and  myself,  must  be  left  to  the  judg- 
ment of  investigators  who  are  equally  familiar  with  both  classes 
of  ore-deposits. 

My  statement-,  "  It  is  difficult  to  believe  that  metasomatic 
processes  could  produce  such  pronounced  ore-shoots  as  those 
described*  at  Leadville,"  must  be  explained  from  the  standpoint 
I  have  taken  as  to  the  origin  of  cavities  in  a  soluble  rock.  On 
p.  21  of  my  paper  I  have  shown  that,  before  the  origin  of  the 
cavity,  the  rock-pores  or  interstices  are  filled  with  saturated 
solutions,  and  that  a  line  of  maximum  flow  must  be  subse- 
quently set  up  between  the  point  of  entrance  and  some  point 
of  minimum  resistance,  along  which  line  solutions  not  yet 
saturated,  finding  access  to  the  rock,  may  ultimately  dissolve 
out  open  channels  or  cavities.  These  will  then  possess  a  shape 
extended  in  one  general  direction,  such  as  we  encounter  almost 
always  in  ore-deposits  in  soluble  rocks.  The  Leadville  mining 
engineers  have  established  such  a  form  for  the  Leadville  de- 
posits ;  and  Mr.  Becker  has  also  found  it  in  the  quicksilver-de- 
posits studied  by  him.  If  I  have  correctly  conceived  the  for- 
mation of  these  ore-shoots,  they  should  show  some  indications 
of  free  cavity-formation,  even  when  they  have  been  produced  in 
part  by  the  replacement  of  the  original  rock. 

Finally,  as  regards  the  Eureka  deposits,  I  seem  to  have  been 
misunderstood.  I  did  not  assert  that  the  spaces  originally  oc- 
cupied by  the  Eureka  ore-deposits  had  been  formed  by  surface- 
waters.  I  merely  said  (in  accordance  with  Mr.  J.  S.  Curtis) 
that  this  was  the  case  with  the  caves,  which  accompany  the 
ores  altered  and  redeposited  by  the  action  of  surface-waters. 

Mr.  F.  M.  F.  Cazin  has  called  attention  to  an  American  ex- 
ample, furnished  by  the  Vermont  copper-mine,  in  which  graph- 
ite (or  organic  matter,  the  remains  of  which  are  now  repre- 
sented by  graphite),  may  have  reduced  the  ore-bearing  solutions. 
Mr.  Cazin  cites  the  fossil  palms  converted  into  copper-glance, 
in  the  Trias  of  Mexico,  as  proof  that  the  copper  was  originally 
dissolved  in  the  Triassic  ocean,  though  perhaps  in  too  small  a 
proportion  to  injure  animal  life.  With  regard  to  that  I  must 
observe  that  these  palms  probably  occur  in  a  fresh-water  basin, 
from  which  the  character  of  the  ocean  of  the  period  cannot  be 
inferred ;  nor,  vice  versa,  can  the  traces  of  copper  .found  in 


252  THE    GENESIS    OF    ORE-DEPOSITS. 

corals  be  adduced  as  indicating  the  probable  presence  of  copper 
in  such  a  basin. 

E.  "W.  RAYMOND,  New  York  City :  The  labor  and  pleasure 
of  translating  Prof.  Posepny's  contributions  having  fallen  to 
me,  I  have  taken  special  interest  in  the  discussion  which  they 
have  elicited ;  and  I  venture  to  believe  that  an  attempt  on  my 
part  to  summarize  the  results  thus  far  attained  may  be  useful 
as  a  help  to  the  further  discussion  which  I  trust  will  ensue,  and 
will  not  be  deemed  an  arrogant  assumption  of  the  position  of 
a  judge,  which  is  as  far  from  my  intention  as  it  is  beyond  my 
capacity. 

No  amount  of  latitude  in  such  a  discussion  is  reprehensible 
if  it  elicits  new  facts ;  for  the  accumulation  of  accurate  data  is 
really  more  important  than  the  mere  iteration  of  argument,  and 
a  new  fact,  however  remotely  collateral  in  its  bearing,  may  turn 
out  to  be  of  inestimable  value.  In  this  connection,  however, 
it  should  be  noted  that  the  fact  is  valuable  in  proportion  as  it  is 
not  merely  the  expression  of  an  opinion.  When  we  are  told  by 
some  authority  that  he  "  found  unmistakable  evidences  "  of  this 
or  that,  we  are  simply  asked  to  accept  his  conclusion,  which 
might  or  might  not  have  been  our  own  upon  the  same  phe- 
nomena ;  and  the  weight  we  give  to  the  fact  of  his  opinion  as 
indicative  of  the  real  facts  behind  it,  which  are  what  we  want, 
depends  upon  our  confidence  in  him,  not  only  as  an  observer, 
but  also  as  a  reasoner.  In  my  j  udgment  we  should  be  grateful 
to  Prof.  Posepny  for  the  emphasis  he  has  laid,  not  only  in  this 
paper  but  in  many  preceding  publications,  upon  the  supreme 
importance  of  what  he  has  called  rein  objective  Darstellungen,  a 
phrase  which  I  have  weakened  in  my  translation  by  rendering 
it  " accurate  descriptions,"  in  the  fear  that  the  term  "objective," 
used  in  that  sense,  would  be  misleading.  In  this  connection  I 
may  remark,  that  when  the  admirable  paper  of  Prof.  Posepny 
was  sent  to  me,  it  bore  a  title  which  would  have  been,  literally 
translated,  "  Subjective  Views  on  the  Genesis  of  Ore-Deposits," 
the  author  meaning  thereby  to  indicate  modestly  that  he  offered 
his  paper  only  as  an  expression  of  the  opinions  to  which  he  had 
been  led  by  his  own  studies,  and  not  as  a  statement  of  the  set- 
tled results  of  science..  I  took  the  liberty  of  objecting  to  this 
title,  on  the  ground  that  "  subjective  "  views  might  be  construed 


THE    GENESIS    OF    ORE-DEPOSITS.  253 

as  opinions  simply  "  evolved  from  the  inner  consciousness," 
without  any  foundation  whatever  in  observed  facts ;  and  as  a 
result  of  this  correspondence,  Prof.  Posepny  permitted  the 
use  of  the  simpler  title,  accompanied  with  such  introductory 
explanations  as  would  relieve  him  from  the  imputation  of  dog- 
matism. 

Accepting,  however,  his  use  of  "  subjective'7  and  "objective" 
as  connoting  statements  respectively  affected  or  unaffected  by 
individual  opinion,  we  cannot  but  appreciate  and  shape  his  de- 
sire for  "  purely  objective  "  reports  of  observed  facts  in  the  field 
of  his  studies.  And,  since  it  is  extremely  difficult  to  convey  an 
"  objective  "  description  in  writing,  the  superiority  of  a  careful 
drawing  (not  an  "  ideal  "  diagram,  though  that  has  its  uses,  and 
is  often  a  better  vehicle  of  description  than  words)  is  clear. 
Prof.  Posepny  has  practiced  his  own  doctrine  by  illustrating  his 
paper  with  numerous  drawings,  and,  I  may  add,  he  has  uncon- 
sciously enforced  that  doctrine  by  betraying  his  own  doubts  and 
difficulties  in  the  interpretation  of  mere  verbal  and  partly 
"subjective"  descriptions,  given  by  other  authors. 

The  misunderstandings  thus  occasioned  may  be  left  to  settle 
themselves  through  mutual  explanations,  such  as  have  been 
made,  more  or  less  fully,  in  the  course  of  this  discussion.  It 
need  only  be  added  here  that  Prof.  Posepny's  conscientious  and 
frank  declarations  as  to  the  limits  of  his-personal  observation, 
and  his  careful  references  to  all  authorities  cited,  constitute  a 
safeguard  against  error,  a  full  guide  to  further  investigation  and 
a  model  for  our  imitation.- 

But  the  chief  questions  of  interest  to  us,  I  think,  are  these  : 
"What  are  the  characteristic  and  valuable  contributions  made  by 
this  paper  to  the  theory  of  the  genesis  of  ore-deposits  ?  and, 
What  are  the  definite  issues  on  which  Prof.  Posepny's  views 
differ  from  those  of  other  observers,  as  the  latter  have  been  rep- 
resented in  this  discussion  ? 

Under  the  first  head  I  think  we  may  regard  as  pre-eminent 
the  masterly  exposition  of  the  subject  of  underground  circula- 
tion and  the  distinction  established  between  the  vadose  and  the 
deep  circulation,  the  former  actuated  mainly  by  gravity  and 
conditioned  upon  the  relative  position  of  the  surface-outflow, 
the  latter  complicated  by  the  effects  of  capillarity  and  pressure 
due  to  heat.  This  distinction  supersedes  the  vague  terms 


254  THE    GENESIS    OF    ORE-DEPOSITS. 

"  ascending "  and  "  descending,"  though  the  author  has  em- 
ployed these  terms,  in  accordance  with  popular  usage,  and  has 
thereby  incurred  some  unnecessary  criticism.  For  it  is  really 
not  of  the  slightest  importance  to  the  general  theory  of  this  sub- 
ject whether  a  given  mineral  solution  was  moving  horizontally 
or  up  and  down  when  it  produced  a  given  precipitate.  The 
only  significant  question  is  whether  it  was  on  the  way  up  or 
down ;  that  is,  whether  it  belonged  to  the  one  or  to  the  other 
branch  of  the  underground  circulation.  The  third  view, 
namely,  that  such  a  solution  might  belong  neither  to  the 
vadose  downward  circulation  nor  to  the  deep  upward  circula- 
tion, but  to  a  "  lateral  secretion,"  Prof.  Posepny  practically  de- 
clares to  be  inconceivable.  As  I  understand  his  argument  (or 
rather,  perhaps,  as  I  would  state  my  own  view,  which  I  think 
to  be  in  substantial  accordance  with  his),  it  may  be  expressed 
as  follows : 

1.  The  aqueous   solutions  underground  must  be  conceived 
either  (a)  as  moving  on  a  general  downward  course,  as  parts  of 
the  vadose  circulation,  above  ground-water  level,  or  (6)  as  pen- 
etrating still  deeper  into  the  rocks  below  drainage-level  (the 
barysphere),  or  (c)  as  rising  from  those  depths  under  pressure, 
overcoming  gravity,  towards  or  to  the  surface ;  or  (d)  as  stand- 
ing (held  by  capillarity  or  otherwise)  in  rocks,  whether  above 
or  below  the  drainage-level,  and  not  participating  in  the  circu- 
lation at  all. 

2.  Concerning  the  condition  (a),  which  is  most  open  to  our 
observation,  we  know  a  great  deal.'    We  know,  for  instance, 
from  an  overwhelming  number  of  observations,  that  the  solu- 
tions of  the  vadose  circulation  are  oxidizing,  and  that  (apart 
from  the,  probably  rare,  re-formation  of  sulphides  by  the  ac- 
tion of  organic  matter)  they  do  not  precipitate  sulphides,  but, 
on  the  contrary,  attack  and  decompose  them. 

3.  Concerning  (6),  we  know  nothing  by  direct  observation, 
but  are  forced  to  believe,  and  justified  (by  Daubree's  experi- 
ments, etc.)  in  believing,  that  such  a  movement  actually  takes 
place. 

4.  Concerning  (c),  we  have  the  evidence  derived  from  hot 
springs,  etc.,  which  has  convinced  all  observers  that  there  is  in 
fact  such  an  ascending  circulation,  whatever  may  be  their  con- 
clusions as  to  the  depth  of  its  origin  or  the  degree  of  its  agency 


THE   GENESIS    OF   ORE-DEPOSITS.  255 

in  forming  mineral  deposits.  The  ascension-theory  postulates 
concerning  it  only  that  it  comes  from  the  depths  below  drain- 
age-level, and  is  not  moved  merely  by  siphon-action,  ultimately 
due  to  gravity. 

5.  Concerning  (d),  it  may  be  said  that  solutions  thus  held  with- 
out participation  in  the  general  circulation,  while  they  may  affect 
internal  changes  in  the  rocks  they  occupy,  cannot  begin,  until 
they  begin  to  move,  a  process  of  redistributing  and  concentrating 
by  precipitation  elsewhere  the  substances  they  hold  in  solution. 

6.  Moreover,  solutions  in  the  condition  (d),  though  not  par- 
ticipating in  the  general  circulation,  must  have  reached  their 
locus  by  means  of  that  circulation.     They  must  be  conceived  as 
having  been  a  part  either  of  the  downward  or  of  the  upward 
branch,  or,  in  other  words,  as  arrested  portions  of  the  circula- 
tion. 

7.  Whenever  they  begin  to  move,  they  must  join  one  or  the 
other  branch  of  the  circulation;  .and  the  deposits  they  may 
make  must  be  the  result  of  the  laws  of  that  branch,  operating 
upon  the  nature  of  the  solutions,  this  in  turn  being  partly  de- 
pendent upon  their  original  source. 

8.  There  is,  therefore,  no  room  for  a  hypothesis  of  ore-con- 
centration and  deposit  in  bodies  of  considerable  size  by  "  secre- 
tion," independent  of  circulation,  or  for  a  cycle  of  circulation, 
complete  in  itself,  yet  not  participating  in  the  general  phenomena 
described.   For  continuous  currents  must  come  from  somewhere 
and  go  somewhere ;  and  neither  inflow  nor  outlet  is  provided, 
except  by  the  conditions  of  the  general  underground  circulation, 
as  described. 

9.  From  this  standpoint  it  is  clear  that  the  source  of  the  sub- 
stances carried  in  solution  by  a  current  must  lie  somewhere  in 
the  path  which  that  current  has  traversed.     If  the  theory  of 
lateral  secretion  means  no  more  than  the  assertion  that  the 
mineral  solutions  which  have  precipitated  ore  in  a  given  fissure 
or  space  have  traversed  and  leached  some  rock  before  entering 
that  space  and  that  this  rock  adjoined  or  lay  in  "  reasonable 
proximity  "  to  the  space  of  deposition,  it  would  mean,  as  to  the 
first  proposition,  nothing  that  anybody  denies ;  while  as  to  the 
second  proposition,  it  would  be  a  somewhat  vague  assertion, 
requiring  definite  proof  in  each  case,  and  not  entitled  to  the 
dignity  of  a  general  theory. 


256  THE    GENESIS    OF    ORE-DEPOSITS. 

10.  But  the  theory  of  lateral  secretion,  however  it  may  have 
melted  away  under  the  fire  of  criticism,  originally  claimed  more 
than  this.  Prof  Sandberger  says:* 

"The  so-called  descension-theory  of  Werner  is  purely  neptunic,  and  regards 
veins  as  exclusively  filled  from  above  downwards  by  the  deposition  of  ores  from 
liquids,  without  answering  the  question,  whence  these  liquids  derived  their  me- 
tallic contents.  The  descension-theory  remains  good  to-day  for  all  cases  where,  in 
higher-lying  rocks,  those  substances  can  be  with  certainty  traced,  which  have  col- 
lected as  ore-deposits  in  cavities  and  fissures  in  lower-lying  rocks,  not  originally 
containing  them.  If  the  ores  are  accumulated  in  fissures,  they  possess  all  the 
characters  of  fissure-veins.  So  far  as  my  knowledge  of  ore-deposits  goes,  the 
filling  of  fissures  by  ores  which  can  be  clearly  proved  to  have  filtered  in  from 
above  is  not  very  frequent ;  but  such  filling  of  irregular  cavities  are  common." 

After  mentioning  as  an  excellent  instance  the  lead-  and  zinc- 
deposits  of  Kaibl  (which  Prof.  Posepny  has  discussed  with  very 
different  conclusions),  and  declaring  that  he  is  at  present  con- 
cerned specially,  not  with  such  deposits,  but  with  true  fissure- 
veins,  Prof.  Sandberger  proceeds  to  state  as  follows  the  ascen- 
sion theory,  which  he  says  "  still  counts  many  adherents,"  and 
which  he  proposes  to  controvert : 

"The  ascension-theory  assumes  in  all  cases  that  the  ores  occurring  in  a  vein- 
fissure  were  derived  either  not  at  all,  or  only  in  part,  from  the  immediately  ad- 
jacent country-rock  (aus  dem  unmittelbaren  Nebenyestein),  but,  on  the  contrary,  from 
greater  depths,  and  have  been  introduced  into  the  fissures  either  by  ascending 
mineral  springs  or  by  sublimation.  The  substances  deposited  in  the  veins  should 
therefore  be  different  from  those  of  the  adjacent  rock,  and  should  only  occur  in 
the  latter  as  lateral  impregnations  from  the  fissures." 

Confining  himself  to  the  supposed  agency  of  ascending  min- 
eral springs,  the  author  asserts  that  such  springs  would  not,  and 
in  fact  do  not,  deposit  minerals  in  their  channels,  and  discusses 
at  some  length  the  case  of  Sulphur  Bank  in  California,  which 
he  declares  to  be  the  only  instance  apparently  contradicting  his 
view.  He  argues  against  the  conclusions  drawn  by  others  from 
this  instance,  and  concludes  as  follows  (p.  17)  : 

"If,  then,  the  only  region  in  which  it  has  been  deemed  possible  to  assume  the 
filling  of  vein-pressures  by  ascending  mineral  springs  as  a  process  now  going  on, 
furnishes  no  trustworthy  proofs  of  this  assumption,  what  remains?  In  my  opinion, 
only  the  leaching  of  the  country-rock  which  bounds  the  fissures  by  seepage-waters 
which  have  penetrated  it,  and  which  deposit  the  dissolved  materials  as  ores  and 

*  Untersuchungen  uber  Erzgange,  von  Fridolin  Sandberger.  Wiesbaden,  1882, 
Erstes  Heft,  pp.  3,  4. 


THE    GENESIS    OF    ORE-DEPOSITS.  257 

gangue  in  the  fissures  of  the  same  (or,  in  exceptional  cases,  the  nearest  neighbor- 
ing) rock.*  This  is  the  so-called  lateral-secretion  theory  in  its  most  prosaic  form  ; 
and  it  is  this  to  which  I  have  been  so  distinctly  led  by  many  years  of  observation 
and  investigation  that  I  am  forced  to  consider  it  applicable  to  most  ore-veins." 

11.  It  is  clear  that  this  theory  contemplates  the  exclusion 
of  the    agency  of  waters   rising   from   below   drainage-level. 
That  there  are  such  waters,  is  an  admitted  fact;  and  it  must 
be  also  admitted  that  they  are  under  pressure  great  enough  to 
overcome  gravity  and  friction.     All  fissures  accessible  to  such 
waters,  they  must  necessarily  occupy;  and  it  seems  to  follow 
inevitably    that   all    fissures    extending    below   drainage-level 
must  be  filled,  up  to  that  level  at  least,  with  waters  either 
in   actual    circulation  on   their   way   upward,  or   temporarily 
arrested  and  confined.     "  Seepage  "  into  such  spaces  is  incon- 
ceivable. 

12.  On  the  other  hand,  currents  under  pressure  would  neces- 
sarily penetrate   into  the  pores  and  interstices  of  the  rocks 
bounding  their  main  channels,  and  the  deposit  in  such  rocks 
of  minerals  carried  from  the  fissures  is  more  probable  a  priori 
than  the  deposit,  in  the  fissures,  of  minerals  dissolved  from  the 
adjoining  rocks.     The  opposite  would  be  true  if  the  fissures  did 
not  contain  water,  a  condition  which  can  only  be  assumed  when 
there  is  a  lower  outlet,  that  is  to  say,  only  in  the  zone  of  vadose 
circulation. 

13.  The  advocates  of  lateral  secretion  must  state,  at  least, 
their  conception  of  the  way  in  which  "  seepage  "  can  take  place 
from  a  porous  solid  holding  water  into  an  adjoining  space  also 
filled  with  water,  and  under  high  pressure.     That  practically 
no  interchange  between  the  two  will  take  place,  even  if  the 
pressures  are  equal,  is  shown  by  the  occurrence  of  fresh-water 
springs  along  our  coast,  separated  by  a  few  feet  of  sand  only 
from  the  salt  waters  of  the  sea.     It  is  often  popularly  supposed 
that  the  sea-water  has  been  deprived  of  its  salt  by  "  filtration  " 
through  the  sands  ;  but  the  real  fact  is,  that  the  mass  of  the 
sea  bars  the  path  of  a  circulation  which  would  carry  the  spring- 
water  into  it,  and  the  spring  seeks  another  way  to  the  surface, 

*  "  Nach  meiner  Ausicht  nur  Auslaugung  des  die  Spalten  begranzenden  Nebenge- 
steins  durch  Sickerwasser,  welche  dasselbe  durchdrungen  haben,  und  die  gelosten 
Stoffe  als  Erze  und  Gangarten  in  den  Spalten  des  gleichen  oder  ausnahmsweise 
auch  in  solchen  des  nac listen  Nachbargesteins. " 


258  THE    GENESIS    OF    ORE-DEPOSITS. 

where  it  emerges  perfectly  fresh.  The  intervening  sands  are 
doubtless  filled  with  brackish  water,  but  this  takes  no  part  in 
the  circulation,  and  therefore  carries  no  salt  into  the  channel 
of  the  spring.  If  the  Atlantic  Ocean  cannot  "  seep  "  salt  into 
a  spring  of  fresh  water,  how  could  a  rock,  not  included  in  the 
path  of  a  continuous  circulation,  impregnate  any  portion  of  that 
path  by  its  "  seepage  ?" 

14.  Again,  it  is  conceivable  that  gash-veins,  and  other  spaces 
wholly  within  a  given  rock-mass,  may  receive   concentrations 
of  mineral  by  "  seepage,"  though  even  in  this  case,  if  the  pro- 
cess is  to  result  in  considerable  accumulations  of  mineral,  it 
must  be  a  long-continued  one,  supported  by  an  inflow  and  out- 
flow ;  in  other  words,  it  must  be  a  part  of  a  general  ascend- 
ing or  descending  circulation.     And  since  the  ascending  cir- 
culation   involves    a   pressure   from   the   fissure   towards   the 
wall-rock,  that  is,  in  the  wrong  direction  for  "  seepage,"  it  fol- 
lows that,  except  in  the  vadose  region,  and  apart  from  highly 
exceptional  conditions,  the  products  of  the  leaching  of  any 
given  rock-mass  are  not  likely  to  be  found  predominantly  in 
adjoining  fissures. 

15.  The  theory  of  lateral  secretion,  therefore,  is  essentially 
confined  to  the  region  of  the  vadose  circulation ;  and  those  who 
would  apply  it  to  the  origin  of  deposits  containing  sulphides 
must  be  prepared  to  maintain  that  those  sulphides  have  been 
deposited  from  solutions  moving  downwards  or  laterally,  under 
the  influence  of  gravity,  in  other  words,  surface-waters.     Prof. 
Sandberger  does  not  hesitate  to  accept  this  alternative,  although 
he  does  not  perceive,  apparently,  how  it  confines  the  sphere  of 
his  theory.    According  to  his  view,  the  metals  are  disseminated 
in  the  country-rocks  and  silicates,  and  these  rocks  contain  also 
sulphate  of  soda,  and  other  soluble  alkaline  sulphates,  as  well 
as  chloride  of  sodium,  all  of  which,  he  supposes,  are  converted 
by  organic  matter  into  alkaline  sulphides,  which  transform  the 
metallic  silicates  into  metallic  sulphides. 

16.  But  this  explanation  encounters  two  serious  difficulties. 
In  the  first  place,  it  is  opposed  to  the  overwhelming  evidence 
that  the  downward  circulation  does  not  characteristically  de- 
posit sulphides,  but  attacks  them ;  that  it  does  not  character- 
istically contain  alkaline  sulphides,  but  alkaline  carbonates  and 
free  carbonic  acid  and  oxygen.     In  the  second  place,  the  expla- 


THE    GENESIS    OF    ORE-DEPOSITS.  259 

nation  breaks  down  in  the  presence  of  fissures  filled  with  sul- 
phides, extending  far  below  any  present  or  conceivable  past 
drainage-level.  The  sulphide  ore-deposits  in  such  fissures,  at 
the  greatest  depths  attained  by  mining,  show  no  structural  dif- 
ferences or  other  indications  of  a  different  origin,  as  compared 
with  sulphides  in  the  levels  above.  There  is  a  change  at  water- 
level,  but  it  is  notoriously  a  change  from  oxidation  above,  to 
absence  of  oxidation  below,  that  level. 

17.  The  lateral-secretion  theory,  therefore,  so  far  as  it  is  true 
at  all,  is  no  more  than  a  subordinate  division  of  the  theory  of 
the  formation  of  deposits  in  open  spaces  above  drainage-level ; 
and  even  here  it  is  neither  necessary  nor  plausible,  as  the  ex- 
planation of  deposits  which  continue  downward,  and  must  be 
referred,   as  regards  their  lower   portion,  to  a  deep  source. 
Such  deposits  may  have  been  altered  in  character,  and  even  in 
form,  in  the  vadose  region;  they  probably  originated  in  the 
deep  region. 

18.  On  the  other  hand,  the  hypothesis  of  ascending  waters 
as  the  vehicle  of  solution  and  deposition  does  not  exclude  the 
idea  of  the  leaching  of  any  rock  traversed  by  such  waters.     It 
indeed  assumes  such  a  leaching  as  having  taken  place  some- 
where.   But,  as  opposed  to  the  theory  of  lateral  secretion  (mod- 
ified to  lateral  circulation)  it  assumes  the  rock  immediately 
adjoining  a  vein-fissure  (when  the  fissure  continues  deeper)  to  be 
the  least  likely,  not  the  most  likely,  source  of  the  metallic  ores. 
And  on  this  point  it  appeals  to  the  phenomena  of  crustification. 
Nothing  is  plainer  than  the  evidence  afforded  by  the  successive 
crystalline  crusts  of  an  amethyst  geode,  for  instance,  that  the 
deposition  took  place  first  upon  the  walls  of  the  cavity,  after- 
ward upon  the  crust  thus  formed,  and  so  on  toward  the  cen- 
tral druse.     The  very  first  deposit  evidently  covered  the  wall 
with  an  impermeable  layer ;  and  the  material  for  all  succeeding 
deposits  must  have  come  (as  the  sections  of  many  geodes  show 
visibly  that  it  did  come),  through  a  passage  from  without  the 
mass  of  the  geode.     In  like  manner,  the  crustified  filling  of  a 
fissure-vein  cannot  well  have  come  from  the  walls  of  the  vein 
at  the  place  where  the  first  crust  deposited  would  necessarily 
close  those  walls.    The  crusts  have  been  deposited  from  a  solu- 
tion between  them.     The  central  druse  was  not  first  formed, 
and  then  pushed  out  by  successive  deposits  behind  it,  as  the 

17 


260  THE    GENESIS    OF    ORE-DEPOSITS. 

bark  of  a  tree  is  thickened.  The  solution  depositing  the  crys- 
tals in  successive  crusts  must  therefore  have  been  part  of  a 
current ;  and  its  entrance  and  exit  can  scarcely  be  sought,  as  a 
rule,  in  the  walls  it  has  crusted.  A  side-fissure,  entering  through 
either  wall,  is,  of  course,  not  impossible  or  uncommon.  But  it 
cannot  be  assumed  to  exist  without  proof.  And  when  such  a 
thing  is  actually  found,  its  effect  upon  the  vein  is  so  marked  as 
to  raise  a  strong  presumption  that  the  normal  source  of  the 
vein-solutions  was  not  in  that  direction. 

19.  Prof.  Posepny  has  laid  much  emphasis  upon  crustifica- 
tion,  as  he  has  denned  that  term.     I  think  he  is  right  in  so 
doing;   and  I  may  remark  incidentally  that  his  use   of  new 
special  terms  (which  has  been  objected  to  by  some)  is  justified, 
in  this  case,  as  in  other  cases,  by  the  greater  precision  of 
thought  thereby  secured.     The   disadvantage  of  a  preference 
for  ordinary  and  familiar  words,  when  such  words  may  have 
many  meanings,  is  illustrated  by  the  manner  in  which  Prof. 
Posepny,  on  the  one  hand,  and  his  critics,  on  the  other,  have 
been  misled  by  the  ambiguity  of  "  banded  structure."     He  in- 
terprets "  banded  structure,"  or  equivalent  expressions,  in  some 
of  the  authorities  he  cites,  as  meaning  crustification,  and  they 
say  that  banded  structure  may  arise  in  several  ways,  intimat- 
ing thereby  that  crustification  is  not  a  sure  proof  of  deposition 
upon  cavity-walls.     The  verbal  misconception  being  corrected, 
it  seems  to  me  that  there  is  no  difference  between  the  parties 
on  this  head. 

20.  The  assertion  that  a  current  is  necessary  for  the  deposi- 
tion of  such  crustified  accumulations  is  not  to  be  construed  as 
excluding  variations  in  velocity,  or  occasional  stoppages  and  in- 
termissions.    The  objection  of  Prof.  Sandberger,  that  mineral 
springs  do  not,  as  a  fact,  deposit  solid  substances  in  their  chan- 
nels, seems  to  be  based  upon  the  conception  of  such  springs  as 
ascending  with  unvaried  velocity,  as  if  through  pipes  of  uni- 
form diameter.     Even  pipes,  as  Professor  Posepny  reminds  us, 
have  been  known  to  receive  interior  incrustations;  but  the 
probability  of  such  deposits  is  much  increased  when  the  effects 
of  variations  in  the  nature  and  size  of  the  channel  are  taken 
into  account.     Mutatis  mutandis,  the  analogy  of  the  deposition 
of  sediments  by  a  running  stream  ie  available  here.     As  sands 
and  clays,  carried  in  suspension  where  the  current  is  most  rapid, 


THE    GENESIS    OF    ORE-DEPOSITS.  261 

are  dropped  where  it  is  checked  through  widening  of  the  chan- 
nel, or  from  other  causes,  so  the  deposits  of  a  mineral  circula- 
tion will  naturally  be  greatest  where  the  movement  is  slowest, 
or  is  even  temporarily  arrested  altogether ;  and  they  will  be  re- 
duced to  a  minimum,  other  things  being  equal,  where  the  cur- 
rent is  most  rapid.  The  phenomenon  of  distinct  crustification, 
in  fact,  requires  the  hypothesis  of  a  relative  quiescence  of  the 
menstruum.  And  instances  are  not  wanting  underground  in 
which  the  widening  of  the  vein-fissures,  or  the  change  to  a 
flatter  dip,  has  apparently  favored  the  deposition  of  ore.*  The 
ascension-theory  does  not  exclude  these  obvious  considerations. 
All  it  asserts  is,  that  the  portion  of  solution  entering  a  given 
space,  and  depositing  therein  a  precipitate,  must  thereafter 
escape  and  give  place  to  another  portion  of  solution,  if  the  pro- 
cess is  to  be  repeated ;  and  that,  with  regard  to  deposits  of  sul- 
phides, formed  below  drainage-level,  the  only  escape  is  ulti- 
mately upward.  But  the  phenomena  of  crustification  in  veins 
afford,  in  my  judgment,  another  argument  against  the  theory 
of  lateral  secretion.  Namely,  it  is  well  known' that  the  crusti- 
fication, even  in  typical  fissure-veins,  is  not  everywhere  distinct. 
If  it  can  be  observed,  with  its  characteristic  central  druse,  in 
one  part  of  a  vein,  it  is  held  (properly,  I  think)  to  be  (in  the 
absence  of  evidence  to  the  contrary)  a  proof  that  the  similar 
ores  of  other  parts  of  the  vein  have  been  similarly  deposited. 
The  absence  of  crustification  in  some  places  may  be  explained, 
on  the  ascension-theory,  by  the  varying  speed  of  the  current, 
and  the  varying  nature  and  dip  of  the  walls,  as  affecting  the 
deposition  of  adherent  crystalline  crusts.  The  chemical  or 
physical  causes  inducing  precipitation  may  simply  produce  a 
suspended  precipitate,  to  be  subsequently  deposited  as  a  sedi- 
ment. But  if  lateral  secretion  has  produced  crustification,  such 
as  is  observed  in  fissure-veins  (as  I  think,  with  Professor  Po- 

*  On  the  other  hand,  increased  width  of  ''vein-matter  "  has  often  been  due  to 
a  splitting  of  the  fissure,  and  the  enclosure  of  fragments  of  country-rock,  which 
is  afterward  more  or  less  transformed  into  gangue,  or  remains  as  horses  in  the 
vein.  Or,  such  increased  width  may  be  (as  in  the  Cornwall  tin-mines)  the  re- 
sult of  a  mineralization  of  the  country-rock  beyond  the  limits  of  the  original 
fissure,  producing  a  mass  of  altered  rock  impregnated  with  ore  (the  Zinnzwitter 
of  the  Germans).  In  such  cases,  while  the  aggregate  of  mineral  deposited  is 
doubtless  much  greater  than  it  would  have  been  had  the  solution  passed  through 
the  narrow  fissure  only,  the  richness  of  the  material  is  reduced  by  the  admix- 
ture of  gangue  and  rock. 


262  THE    GENESIS    OF    ORE-DEPOSITS. 

sepny,  that  it  has  not),  then  that  structure,  it  seems  to  me, 
should  be  more  uniformly  distinct  in  such  veins  than  it  is.  For 
the  conception  of  lateral  secretion  into  a  fissure  excludes  the 
conception  of  a  current  under  higher  pressure,  already  occupy- 
ing that  fissure ;  and  the  local  interference  of  such  a  current 
with  the  quiet  process  of  crystallization  is  therefore  out  of  the 
question. 

21.  The  comparatively  small  amount  of  mineral  matter  con- 
tained in  the  ascending  springs  of  the  deep  circulation,  origi- 
nating below  drainage-level,  is  to  my  mind  some  indication  that 
they  have  already  deposited  somewhere  the  larger  part  of  the 
substances  they  have  held  in  solution.     They  are  never  satu- 
rated solutions.     As  we  find  them,  they  contain  what  we  may 
suppose  to  be  only  remaining  traces  of  the  metallic  constitu- 
ents which  they  may  (we  may  almost  say  must)  have  carried 
at   greater   depths,  temperatures,   and  pressures.     Is  not  the 
presence  of  these  minute  remainders  really  an  evidence  of  the 
larger  amounts  once  present,  and  therefore  of  a  precipitation 
en  route  ?     In  connection  with  this  question,  the  probable  con- 
ditions of  the  deep  zone  must  be  borne  in  mind,  such  as,  not 
only  the  increased  solvent  power  of  the  waters  of  that  zone, 
but  also  the  probable  slowness  of  their  downward  progress, 
which   is   practically  (according  to  Daubree)   a  seepage,  and 
which  must  favor  the  formation  of  saturated  solutions. 

22.  In  reply  to  this  suggestion,  the  question  may  be  raised 
how  the  deposition  of  ores,  extending  almost  or  quite  to  the 
surface,  is  to  be  accounted  for,  if  the  solutions  now  encountered 
below  drainage-level  are  already  so  nearly  exhausted  as  to  be 
capable  of  comparatively  little  further  precipitation.     Without 
forgetting  that  the  most  dilute  solutions  may  still  give  precipi- 
tates under  chemical  or  physical  changes  of  condition;  and  that 
such  precipitates,  however  insignificant,  may  attain  a  consider- 
able aggregate  amount  by  long-continued  repetition,  I  think  the 
more  comprehensive  answer  to  the  above  question  is  found  in 
the  conclusion  to  which  we  are  led  by  the  ascension-theory,  that 
deposits  carrying   metallic    sulphides,  though  they  reach  the 
present  surface,  were  formed  mainly  below  the  influence  of  the 
vadose  circulation,  and  therefore  under  conditions  such  as  may 
now  obtain  at  depths  beyond  our  observation. 

23.  This  suggests  another  point,  to  which  Prof.  Posepny  has 


THE    GENESIS    OF    ORE-DEPOSITS.  263 

called  attention,  and  which  was  acutely  recognized  by  Cotta, 
many  years  ago,*  namely,  the  fact  that  speculations  upon  the 
relation  between  the  contents  of  mineral  veins  and  their  depth 
are  largely  vitiated  by  the  vagueness  and  uncertainty  of  the  ele- 
ment of  depth,  as  estimated  by  comparison  with  the  present 
surface.  In  most  mining  regions  there  is  unquestionable  evi- 
dence of  great  denudation,  which  has  probably  removed  from 
the  surface  a  larger  mass  than  has  been  penetrated  anywhere  by 
mining.  It  seems  impossible,  therefore,  to  argue  as  to  the  con- 
tinuance of  ores  "  in  depth,"  meaning  thereby  beyond  1000  or 
2000  feet  from  the  present  surface,  when  that  surface  itself  may 
have  been  10,000  feet  underground  at  the  time  the  ores  were 
deposited.  We  may  imagine  that  the  ascending  waters  in  a 
vein  now  rich  in  metallic  deposits  "  from  the  grass-roots  down," 
once  continued  their  upward  course  to  the  former  surface, 
emerging  as  dilute  solutions ;  or  never  reached  that  surface  in- 
tact, but  encountering  the  vadose  circulation,  became  a  part  of 
it ;  and,  in  either  case,  precipitated  less  and  less  metallic  matter 
as  they  ascended.  Conversely,  we  may  reasonably  imagine 
that,  if  we  could  retrace  the  course  of  a  mineral  spring  coming 
from  the  deep  zone,  it  might  lead  us  back  to  the  region  where 
it  had  deposited  the  treasure  of  which  it  now  exhibits,  at  most, 
only  faint  remaining  traces.  And  what  we  might  thus  fairly 
imagine  concerning  an  actual  spring  might  be  equally  true  of 
the  channel  of  a  former  spring  now  closed  altogether,  or  occu- 
pied only,  under  changed  conditions  of  altitude  and  drainage, 
by  the  vadose  circulation — that  is  to  say,  of  a  fissure-vein,  com- 
paratively barren  or  lean  at  the  present  surface.  In  other 
words,  the  present  surface  is  an  arbitrary  section,  cutting  off 
the  veins.  Those  w7hich  it  happens  to  intersect  in  their  richer 
portions  are  naturally  the  ones  which  are  developed  by  mining. 
Those  which  it  showrs  to  be  locally  barren  are  naturally  not 
thus  developed,  unless  local  experience  supports  the  hope  that 
they  will  improve  in  depth.  Such  a  local  experience  is  doubt- 
less the  foundation  of  the  maxim  which  Cornish  miners  have 
carried  throughout  the  world,  that  "  a  fissure-vein  grows  richer 
in  depth,"  a  proposition  for  which,  as  a  general  guide  for 
mining  (apart  from  the  effects  of  surface-waters,  which  may  be 

*  Die  Lehre  von  den  Erzlagerstdtten,  Freiberg,  1858.     Part  I.,  p.  129. 


264  THE    GENESIS    OF    ORE-DEPOSITS. 

sometimes  impoverishing),  is  without  foundation  in  experience. 
For  although  a  comparatively  barren  fissure  may  be,  and  has 
often  been  shown  to  be,  the  upper  part  of  a  vein  carrying  rich 
ores  below,  there  is  no  general  law  that  it  must  be  so;  and, 
moreover,  there  is  no  way  of  determining  a  priori  the  depth  of 
the  barren  zone,  measured  from  the  present  surface. 

24.  On  the  other  hand,  while  the  varying  positions  of  the 
present  surface  prevent  generalization  as  to  the  relations  of  ore 
to  "  depth,"  it  is  unquestionably  possible  that  there  may  be,  in 
a  given  fissure,  a  relation  of  that  kind.     The  ascension-theory 
neither  asserts  nor  denies  such  a  supposition.     Mr.  Rickard's 
suggestion  that  the  deeper  zone  must  be  the  region  of  solution, 
and  a  higher  zone  the  region  of  precipitation,  is  speculatively 
reasonable  enough ;  but  it  amounts  to  a  proposed  subdivision 
of  the  barysphere  into  two  regions ;  for  the  deep  zone  which 
Prof.  Posepny  has  called  the  barysphere  includes  everything 
below  our  observation,  and  it  is  in  that  zone  that  both  solution 
and  precipitation  are  supposed  to  have  taken  place  to  form  the 
deposits  of  metallic  sulphides.     In  our  ignorance  of  the  con- 
ditions of  that  unknown  region,  it  is  scarcely  possible  or  neces- 
sary to   frame   hypotheses    concerning   them.     The   practical 
bearing  of  Mr.  Rickard's  suggestion  lies  in  his  connection  of 
it  with  an  alleged  general  phenomenon  of  the  impoverishment 
of  veins  in  depth,  as  shown  by  experience  in  mining. 

25.  As  to  this  alleged  general  phenomenon,  I  would  say  first, 
that  even  if  it  were  proved,  it  could  hardly  be  ascribed  to  the 
cause  suggested  by  Mr.  Rickard,  namely,  the  predominance  of 
solution  in  lower  zones  and  the  confinement  of  precipitation  to 
higher  ones,  because  the  depths  reached  in  mining  are  not  great 
enough  to  warrant  such  a  deduction,  and  also  because  the  in- 
stances (such  as  Przibram)  of  rich  ores  continuing  for  great 
vertical  distances,  and  down  to  levels  among  the  deepest  ever 
opened  by  mining,  contradict  the  hypothesis. 

But  it  must  be  confessed  that  there  is  much  evidence  which 
seems  to  corroborate  Mr.  Rickard's  statement  as  to  the  ex- 
haustion of  mines  in  depth.  This  evidence  needs,  however,  to 
be  carefully  collated  and  critically  sifted,  before  it  can  be  ac- 
cepted as  the  indication  of  a  natural  law. 

a.  In  such  an  inquiry  all  cases  must  be  rejected  in  which 
oxidized  surface-ores  have  been  mined  down  to  water-level, 


THE    GENESIS    OF    ORE-DEPOSITS.  265 

and  the  mine  has  been  abandoned  by  reason  of  treating  the  re- 
fractory sulphides.  In  many  such  cases  the  oxidized  ores  are 
actually  richer  (e.g.  in  gold)  by  reason  of  the  alteration  they 
have  undergone ;  but  this  is  not  pertinent  to  the  question  of 
original  deposition. 

b.  The  abandonment  of  mines  by  reason  merely  of  the  in- 
creased cost  of  deep  mining  must  be  also  set  aside  as  affording 
no  evidence  on  this  subject. 

c.  The  fact  that  in  mining  a  bonanza  is  traversed,  and  a  rel- 
atively barren  zone  occurs  below,  does  not  necessarily  indicate 
a  relation  between  barrenness  and  depth.     The  occurrence  of 
a  bonanza  very  frequently  involves  barrenness  of  the  neighbor- 
ing portions  of  the  vein.     That  this  is  the  case  on  a  horizontal 
line  is  abundantly  proved.     An  instance  in  point  is  furnished 
by  the  Bullion  mine  situated  on  the  Com  stock  lode,  between 
mines  which  have  produced  many  millions.     The  expenditure 
of  millions  on  the  Bullion  never  produced,  so  far  as  I  know,  a 
ton  of  profitable  ore.     Why  should  not  a  similar  alternation  of 
rich  and  barren  places  occur  in  the  vertical  line  ?     The  cost  of 
exploration  in  depth,  and  particularly  in  sinking,  naturally  dis- 
courages mine-owners ;  and  the  abandonment  of  an  operation 
under  such  circumstances  really  proves  nothing. 

d.  In  any  case  of  alleged  impoverishment  of  a  vein  in  depth, 
not  only  the  actual  depth  below  the  present  surface,  but  also 
(so  far  as  it  can  be  estimated)  the  probable  amount  of  denuda- 
tion which  the  surface  has  undergone,  should  be  taken  into 
account. 

e.  The  nature  of  the  ore  also  may  have  a  distinct  bearing 
upon  this  inquiry.     It  is  my  impression  that  of  the  loose  and 
vague  evidence  thus  far  accumulated,  a  large  part  refers  to  gold- 
ores,  and  particularly  to  free  gold  in  quartz,  as  "  giving  out " 
in  depth.     I  remember  that  in  my  last  conversation  with  the 
late  Joshua  E.  Clayton,  a  close  and  conscientious  observer,  he 
told  me  that  he  had  personally  examined  numerous  quartz- 
veins,  occurring  all  along  the  flanks  of  the  Sierra  Nevada,  and 
had  found  in  every  case  that  the  veins,  as  exposed  in  the  deep 
canons  cross-cutting  them,  hundreds  of  feet  below  their  out- 
crops on  the  mountains,  were  poorer  in  gold  than  at  the  higher 
level.     This  testimony  is  valuable,  and  it  may  be  that  it  indi- 
cates a  general  law  as  to  such  gold- veins ;  but  it  must  be  borne 


266  THE    GENESIS    OF    ORE-DEPOSITS. 

in  mind  that  some  of  the  California  gold-mines  have  been 
worked  deeper  than  any  canons  have  cut  the  veins.  Yet,  011 
the  other  hand,  many  of  the  deep  gold-mines  of  the  State  have 
been  ultimately  abandoned. 

26.  Mr.  Bickard's  suggestion  has  a  practical  side  of  great 
importance.     Namely,  although,  in  my  judgment,  there  is  no 
established  general  law,  discouraging  the  exploration  of  a  vein 
in   depth,  so  long  as  the  fissure  continues  well-defined,  and 
especially  if  it  carries  any  thread  of  ore,  it  is  undoubtedly  the 
case  that  mining  explorations  are  too  much  confined  to  sinking 
and  drifting,  and  that  there  is  too  little  cross-cutting  for  par- 
allel fissures  and  ore-bodies.     To  some  extent  this  is  one  of  the 
results  of  our  absurd  United  States  mining  law,  which  lays  so 
much  stress  upon  the  "apex"  and  the  "lode;"  but  the  mis- 
taken practice  of  neglecting  cross-cuts  into  the  country-rock  is 
not  confined  to  mines  operated  under  that  law. 

27.  Another  important  point  in  Prof.  Posepny's  paper  is  his 
proposition  (based  on  Noggerath's  observations  in  the  main, 
but  not  lacking  other  support)  that  open  spaces  of  dissolution 
may  be  formed  by  ascending  as  well  as  descending  currents. 
Since  the  process  of  solution  depends  upon  the  character  of 
the   liquid   agent,   this   is    only  saying   that   some  ascending 
waters   may  be    able  to  dissolve  portions  of  the  rocks  they 
traverse ;  and  that  if  such  rocks  belong  to  the  class  represented 
by  limestone,  such  currents  may  produce  in  them   caves  and 
channels,  comparable  to  those  notoriously  produced  by  the  de- 
scending waters.     I   confess,  this  seems  to  me  a  reasonable 
proposition,  however  meager  may  be  the  proofs  thus  far  ad- 
duced.   And  I  cannot  understand,  at  all  events,  how  opponents 
of  the  ascension-theory  should  object  to  it;  for  they  do  not 
deny  that  there  are  such  things  as  ascending  mineral  springs, 
and  that  these  springs  hold  in  solution  such  substances  as  car- 
bonates and  free  carbonic  acid.     What  they  deny  is  that  these 
springs  deposit  anything  in  their  channels.     In  that  case,  they 
must  dissolve  without  redepositing ;  and  the  evidence  that  they 
have  actually  excavated  channels  underground  is  afforded  by 
their  constitution.     They  bring  the  evidence  of  their  guilt  with 
them.     To  reply  that  they  are  part  of  the  vadose  circulation 
only,  and  hence,  no   matter  what  their  local  direction,  belong 
to  the  descending  branch,  is  not  permissible ;  for  springs  en- 


THE   GENESIS    OF    ORE-DEPOSITS.  267 

countered  at  great  depths  in  mining  have  the  composition  re- 
quired to  make  them  active  solvents.  How  can  it  be  doubted 
that  the  hot  waters  of  the  springs  encountered  in  the  Bohe- 
mian mines  (see  !N"os.  1,  2  and  3  of  Prof.  Posepny's  table,  p. 
42),  which  contain  "  a  notable  quantity  of  free  carbonic  acid," 
would,  if  they  traversed  limestone,  excavate  cavernous  chan- 
nels in  it  ? 

28.  Moreover,  there  is  reason  why  a  liquid  solvent  under 
pressure,  occupying  a  space  in  a  soluble  rock,  should  eat  its 
way  upward  rather  than  downward  or  laterally — namely,  be- 
cause the  insoluble  portions  of  the  rock,  loosened  by  the  action 
of  the  solvent,  fall  away  from  the  roof  of  the  cavity  most  easily 
and  completely,  leaving  fresh  surfaces  open  to  further  attack. 
Whoever  has  visited,  as  I  have  done,  the  salt-mines  of  the  Salz- 
kammergut,  in  the  Austrian  Tyrol,  where  salt  is  extracted  by 
Sfakwerkcf  and  has  observed  how  the  great  underground  rooms, 
repeatedly  filled  with  water  under  pressure,  travel  upward  through 
the  mass   of  the  saliferous  rock,  as  their  roofs  are  attacked 
and  dissolved,  while  their  floors  are  relatively  protected  by  the 
fallen  insoluble  debris,  can  scarcely  doubt  the  possibility  of  the 
formation  of  spaces  of  dissolution  by  ascending  waters.     One 
variety  of  this  extraction — viz.,  the  so-called  "  continuous  water- 
ing," employed  in  some  of  the  mines — presents  a  still  closer 
analogy.     In  that  method  the  water  is  not  introduced  period- 
ically into  each  Sinkwerk,  to  be  withdrawn  when  saturated,  and 
wholly  replaced  with  fresh  water  for  further  solution.     On  the 
contrary,  the  flow  of  water  is  made  continuous,  fresh  water 
being  admitted  at  one  point  while  saturated  brine  is  conducted 
away  at  another.     It  is  true  that  the  actual  flow  of  the  current 
is   downward,  the  fresh  water  being  admitted  above  and  the 
brine  drawn  off  below;  but  this  is  not  an  essential  feature  of 
the  process  itself.     The  actual  progress  of  excavation  by  solu- 
tion is  upward,  and  the  essential  condition  is  the  presence  of  a 
pressure  sufficient  to  cause  the  solvent  to  penetrate  the  roof. 
That  being  secured,  the  roof  is  mainly  attacked,  the  side  much 
less,  and  the  bottom  scarcely  at  all. 

29.  Prof.  Posepny's  "  Theory  of  the  Sinking  of  Heavier  Con- 

*  Described  in  Serlo's  Leitfaden  zur  Bergbaukunde,  4th  ed.,  Berlin,  1884,  vol.  i., 
p.  611  et  seq. 


268  THE    GENESIS    OF    ORE-DEPOSITS. 

stituents,"  as  applied  to  the  distribution  of  gold,  etc.,  in  placers, 
is  a  valuable  addition  to  our  knowledge  of  such  deposits.  It 
is  highly  desirable  that  our  members  engaged  in  placer  or  hy- 
draulic mining  should  give  us  the  results  of  careful  observa- 
tion upon  the  conditions  presented  by  the  gold-deposits  of 
this  country.  Few  of  them  have  done  so  thus  far,  and  the  field 
is  full  of  interesting  data  not  yet  put  into  shape  for  preserva- 
tion. I  am  inclined  to  think,  for  instance,  that  "the  hypothe- 
sis of  a  natural  concentration  in  running  water,"  which  Prof. 
Posepny  disparages,  and  for  which  he  proposes  to  substitute 
the  theory  just  mentioned,  would  find  some  support  in  the  phe- 
nomena of  many  American  placers,  where  the  gold  is  concen- 
trated not  only  on  a  false  or  true  bed-rock,  but  in  distinct 
channels  along  that  plane,  so  that  the  placer-miners,  for  many 
years,  have  pursued  the  tortuous  channels  of  "  pay-dirt,"  leav- 
ing large  areas  unworked,  which,  for  some  reason  or  other,  did 
not  pay,  though  they  were  equally  "  in  the  gulch,"  and  had  the 
bed-rock  under  them,  like  the  rest.  I  do  not  mean  to  deny  the 
possible  agency  of  such  a  concentration  by  gravity  in  loose 
sands  and  gravels  as  Prof.  Posepny  has  postulated,  but  I 
fancy  it  would  be  hard  to  explain  the  distribution  of  the  gold 
in  many  of  our  American  placers  except  by  including  among 
its  factors  the  action  of  running  water.  If  I  am  correct  in  this 
impression,  I  may  venture  to  consider  the  case  as  one  in  which 
Prof.  Posepny's  heaviest  artillery  can  be  turned  back  upon 
him ;  since  his  theory  of  "  settling  "  may  be  called  a  sort  of 
dry  "  seepage  "  or  secretion  by  gravity,  and  my  view  may  be 
considered  as  the  assertion  that,  here  as  elsewhere,  there  is  no 
deposition  without  circulation. 

Concerning  the  differences  of  opinion  developed  by  this  dis- 
cussion, I  think  it  may  be  said  that,  upon  closer  examination, 
they  are  not  important,  except  as  to  the  explanations  of  certain 
districts  and  ore-deposits  which  Prof.  Posepny  has  rather  de- 
duced from  the  writings  of  others  than  based  upon  observations 
of  his  own. 

With  regard  to  nearly  or  quite  all  of  these  instances,  our  own 
experts  are  not  agreed,  so  that  Prof.  Posepny  has  respectable 
backing  for  his  views,  whether  they  turn  out  in  the  end  to  be 
correct  or  not.  Certainly  he  has  presented  them  with  a  con- 
spicuous absence  of  dogmatism,  and  they  have  been  received 


THE    GENESIS    OF    ORE-DEPOSITS.  269 

on  the  part  of  our  members,  I  am  happy  to  say,  with  the  re- 
spect due  to  the  merits  of  a  veteran  authority,  and  with  grati- 
tude for  the  generosity  which  has  enriched  the  Transactions  of 
the  Institute  with  one  of  the  most  important  contributions  to 
technical  science  ever  made  through  that  medium. 

F.  M.  F.  CAZIN,  Hoboken,  K  J. :  Bergrath  Posepny  rejects 
my  assumption  of  the  presence  of  copper  in  the  Triassic  sea, 
claiming  that  the  evidence  adduced  does  not  hold  good,  and  ob- 
serving, in  support  of  his  view,  "  that  these  palms,"  the  cuprified 
fossils  of  which  are  found  in  the  "  coarse  yellow  sandstones  and 
conglomerates  overlying  the  red  beds  of  the  Trias,"  "  on  the 
junction  of  the  Trias  with  the  Cretaceous,"*  "  probably  occur 
in  a  fresh-water  basin." 

The  fossil  in  question  is  identical  with  "  Podozamites  crassi- 
folia,"  described f  as  occurring  in  the  State  of  Sonora.J  Palms 
cover  at  this  date  a  narrow  belt  along  the  northern  coast  of 
South  America,  disappearing  in  the  interior.  The  location  of 
the  Nacimiento  copper-belt  is  one,  from  which  the  Cretaceous 
sea  retired  last  of  all  on  this  continent.  Its  waters  at  this  date 
are  shed  into  the  Gulf  of  Mexico,  with  no  indication  anywhere 
of  a  pre-existing  barrier.  I  am  acquainted  with  the  English 
and  North  German  Wealden  formation,  having  mined  in  it; 
but,  as  J.  S.  dewberry  did  not,  so  I  did  not,  find  a  trace  of  evi- 
dence for  assuming  a  sweet-water  formation  at  the  Nacimiento 
copper-deposits. 

My  assumption,  therefore,  stands  on  proper  ground,  unless 
more  than  a  probability  to  the  contrary  be  offered. 

*  J.  S.  Newberry,  Report  on  the  Expedition  of  1859,  pages  117  and  118. 

f  Ibid.,  p.  145. 

J  It  is  one  of  the  various  strange  things  observed  in  geological  reports,  that  are 
the  compound  work  of  many — that,  although  J.  S.  Newberry  prominently  and 
repeatedly  refers  to  the  palm-fossils  of  Nacimiento,  his  plates  show  naught  under 
that  head,  but  do  show  a  true  image  of  these  "  palm-leaves,"  described  as  collected 
in  "  quite  a  number "  by  Mr.  Redmond  from  "the  Triassic  strata  at  Los  Broncos, 
Sonora,"  a  locality  not  visited  by  the  expedition  of  which  the  report  is  made.  I 
may  mention,  as  an  amusing  coincidence,  that  at  Prof.  Newberry 's  and  at  my  time 
there  was  at  Nacimiento  a  silver-smith,  who  hailed  from  Los  Broncos,  Sonora, 
and  who,  whenever  in  his  trade  he  needed  copper,  smelted  it  in  a  miniature  cru- 
cible on  a  miniature  Mexican  forge  with  accordion-shaped  bellows,  using  as  his 
material  for  copper  the  fossil  palm-leaves  of  Nacimiento,  of  which  within  easy 
walk  from  his  door  he  could  pick  all  he  was  in  need  of,  and  of  which  he  kept  on 
hand  "  quite  a  number." 


270  THE    GENESIS    OF    ORE-DEPOSITS. 

If  ever  J.  S.  dewberry's  and  my  own  observations  as  to  the 
geological  position  and  normal  character  of  the  deposits  in 
question  have  been  objected  to  on  the  ground  of  actual  local 
observations,  I  am  ignorant  of  the  fact. 

JOSEPH  LE  CONTE,  Berkeley,  Cal. :  All  geologists,  but  espe- 
cially students  of  the  phenomena  of  metalliferous  veins,  are 
under  deep  obligation  to  Bergrath  Posepny  for  the  very  lucid 
exposition  and  abundant  illustrations  of  these  phenomena  con- 
tained in  his  admirable  treatise  on  the  "  Genesis  of  Ore-De- 
posits." Like  the  previous  treatise  of  Sandberger,  though 
taking  an  extreme  opposite  position,  it  must  powerfully  revive 
the  interest  of  students  and  observers  in  the  purely  scientific 
theory  of  metalliferous  veins.  Although  read  at  the  Inter- 
national Engineering  Congress  of  the  World's  Fair  at  Chicago, 
in  1893,  it  has  only  very  recently  fallen  under  my  eye.  As  I 
have  thought  much,  and  published  somewhat  on  this  subject,  I 
beg  leave  to  say  a  few  words  in  the  way  of  criticism  on  this 
masterly  work. 

All,  I  think,  will  agree  that  one  of  the  chief  merits  of  the 
work  consists  in  the  clear  distinction  which  the  author  draws 
between  what  he  calls  the  vadose,  or  superficial,  and  the  deep 
circulation  of  underground  water;  the  water  in  the  one  case 
containing  air,  and  therefore  oxidizing;  in  the  other,  destitute 
of  air,  and  therefore  non-oxidizing ;  the  one  circulation  driven 
by  gravity  alone,  the  direction  of  the  current  being  determined 
by  the  place  of  outflow,  the  other  driven  largely  by  heat  re- 
ceived in  the  lower  parts  of  its  circuit,  and  the  direction  of  its 
current  being  mainly  upward. 

"We  are  all,  I  think,  especially  pleased  with  the  significance 
he  finds  in,  and  the  importance  he  attaches  to,  the  oxidizing 
and  non-oxidizing  effects  of  these  two  circulations  respectively. 
It  follows,  from  this  view,  that  metallic  sulphides  are  not  de- 
posited from  the  waters  of  the  vadose  circulation,  unless  under 
the  exceptional  conditions  of  the  presence  of  excess  of  organic 
matter ;  and  therefore,  that  the  presence  of  metals  in  the  form 
of  sulphides  is  usually  a  sign  of  deposit  from  ascending  currents 
of  the  deeper  non-oxidizing  circulation. 

Most  of  us,  I  think,  too  (and  I  among  the  number),  will  agree 
with  him,  as  against  Sandberger,  that  since  great  deep  fissures 


THE    GENESIS    OF    ORE-DEPOSITS.  271 

are  not  empty,  air-filled  spaces,  but  are  necessarily  filled  with 
water,  deposits  in  them  cannot  take  place  by  seepage  or  oozing, 
or  lateral  secretion  from  the  immediate  bounding-walls.  Also, 
that  the  phenomena  of  crustification  or  ribbon-structure  of  vein- 
contents  seem  to  negative  such  a  mode  of  filling  as  is  supposed 
by  Sandberger ;  that  this  structure  does  not  indicate  a  filling 
by  oozing  and  trickling  of  waters  containing  soluble  matters, 
down  on  a  free  surface,  but  rather  a  deposit  in  successive  layers 
inward  from  water  contained  in  the  fissure. 

For  all  this,  and  very  much  more  which  I  cannot  repeat 
here,  we  are  under  many  obligations  to  Bergrath  Posepny. 
Nevertheless,  I  cannot  but  think  that  he  carries  his  ascension- 
views  much  too  far ;  that  in  his  zeal  against  the  extreme  lateral- 
secretion  views  of  Sandberger,  he  has  gone  to  the  other  extreme 
of  ascensionism ;  and  that  a  truer  view  than  either  may  be  found 
in  one  that  shall  combine  and  reconcile  these  two  extremes. 

The  evidence  of  the  extremeness  of  his. views  is  found,  and 
indeed  is  embodied,  in  his  use  of  the  term  barysphere.  As  con- 
trasted with  lithosphere,  this  term  can  only  mean  a  region  in  the 
interior  of  the  earth,  the  materials  of  which  are  heavier,  because 
more  metalliferous,  than  the  superficial  lithosphere  visible  to  us. 
From  such  a  metalliferous  barysphere,  he  thinks,  all  the  metals 
of  ore-deposits  (with  trifling  exceptions)  are  derived.  It  is  true, 
that  in  his  reply  to  objectors,  he  speaks  of  his  barysphere  as 
only  the  equivalent  of  the  "  unknown  depths  "  of  other  writers ; 
but,  it  must  be  remarked,  that  this  latter  term,  while  open  to 
the  objection  of  indefiniteness,  does  not,  necessarily,  carry  with 
it  any  implication  of  a  region  peculiar  in  its  density  and  in  the 
abundance  of  its  metallic  contents,  although  it  is  doubtless  often 
used  with  this  implication.  The  word  barysphere,  on  the  other 
hand,  fixes  definitely  an  idea  which  has  long  floated  vaguely  in 
the  minds  of  many  writers  on  this  subject.  It  will,  therefore, 
form  the  central  point  of  my  criticism. 

I. — Is  THERE  A  BARYSPHERE  WITHIN  EEACH  OF  CIRCULATING 

WATER  ? 

It  is  true,  that  the  earth  increases  in  density  from  the  surface 
toward  the  center,  and  probably  to  the  very  center  itself.  This 
is  shown  by  the  fact  that  the  mean  density  of  the  earth  is  more 
than  double  that  of  the  superficial  parts.  It  is  true,  also,  that 


272  THE    GENESIS    OF    ORE-DEPOSITS. 

the  increasing  density,  while  certainly  due,  in  part,  to  conden- 
sation by  increasing  pressure,  is  probably  also  due,  in  part,  to 
difference  of  material,  and  especially  to  the  presence  of  metals, 
as  sulphides  or  native,  in  greater  abundance  in  the  interior 
parts.  It  is  true,  therefore,  that  the  deeper  parts  of  the  earth 
are  certainly  heavier,  and  probably  more  metalliferous,  than 
the  superficial  parts.  In  a  word,  it  is  true  that  there  is  a  bary- 
sphere,  and  probably  in  the  sense  used  by  Posepny,  as  being 
more  metalliferous.  But  how  deep  must  we  go  to  find  this 
barysphere  ?  Let  us  see. 

Taking  the  density  of  the  superficial  parts  of  the  earth  (or 
what  Posepny  would  call  the  lithosphere)  at  2.5,  and  the  mean 
density  of  the  earth  as  a  whole  at  5.5  (Posepny  accepts  these 
figures),  and  assuming  the  simplest  rate  of  increase,  viz.,  a  uni- 
form rate,  then  an  actual  density  equal  to  the  mean  density  of 
5.5  would  be  reached  at  the  depth  of  1000  miles,  and  the  central 
density  would  be  1^.5.*  This  is  an  increase  of  3  in  1000  miles. 
At  the  depth  of  100  miles,  therefore,  the  increase  would  be  0.3 
and  the  density  only  2.8.  Is  it  at  all  probable  that  we  ever  have 
circulating  water  coming  up  from  any  such  depth  as  100  miles  ? 
And  yet,  2.8  is  only  about  the  density  of  our  more  basic  erup- 
tives,  and  therefore  wholly  undeserving  the  name  of  a  bary- 
sphere. Circulating  water  may  possibly  come  up  from  as  deep 
as  10  miles,  but  at  the  same  rate  of  increase,  the  density  there 
is  only  2.53 — an  increase  over  the  superficial  density  wholly  in- 
appreciable. Dr.  Raymond,  interpreting  Posepny,  defines  the 
barysphere  as  all  that  interior  region,  the  circulating  water  of 
which  would  not  come  up  at  all  without  the  aid  of  heat.  Does 
this  mean  all  but  the  superficial  region  traversed  by  the  vadose 
or  oxidizing  circulation  ?  If  so,  it  cannot  be  far  from  the  sur- 
face, and  the  term  barysphere,  as  applied  to  it,  is  surely  wholly 
inappropriate  and  misleading. 

But  it  may  be  answered  that  all  this  reasoning  is  based  on 
the  assumption  of  a  uniform  rate  of  increase  of  interior  density  ; 
while  in  fact  the  great  mean  density  of  the  earth  may  be  ex- 
plained by  the  existence  of  a  highly  metalliferous  shell  at  no 

*  By  mathematical  calculation  based  on  the  above  conditions,  an  actual  density 
equal  to  the  mean  density  of  5.5  is  reached  at  depth  of  4  radius  from  the  surface. 
Multiplying  this  gain  of  3  by  4  and  adding  the  surface  density  of  2.5  makes  a  cen- 
tral density  of  14.5  (3X4  +  2.5  =  14.5). 


THE    GENESIS    OF    ORE-DEPOSITS.  273 

great  distance  beneath  the  surface  and  therefore  within  easy 
reach  of  circulating  waters.  To  this  view  I  make  the  following 
objections  : 

1.  All  our  general  reasonings  concerning  the  cause  of  the 
great  mean  density  of  the  earth,  whether  (a)  condensation  by 
increasing  pressure,  or  (6)  arrangement  of  materials  of  a  primal 
fused  earth  according  to  their  relative  specific  gravities,  would 
make  the  increase  progressive  to  the  center.     In  fact  it  is  hard 
to  conceive  the  conditions  under  which  a  dense  metalliferous 
shell  a  little  way  beneath  the  surface  could  be  formed.* 

2.  We  have  abundance  of  materials  coming  up  in  eruptions 
from  depths  as  great  as  circulating  water  is  ever  likely  to  reach, 
and  yet  these  materials  show  no  such  density  and  metalliferous- 
ness  as  is  implied  in  the  term  barysphere. 

But  again,  it  may  be  objected  that  I  greatly  underestimate 
the  depth  which  may  be  reached  by  underground  water.  This 
brings  up  an  important  but  difficult  question.  Is  there  any 
limit  to  the  depth  to  which  meteoric  water  may  penetrate  ?  If 
so,  what  determines  the  limit  and  where  is  it?  These  are 
questions  which  science  is  probably  not  yet  prepared  to  answer 
definitely.  I  once  thought,  that  since  the  pressure  of  a  water- 
column  increases  uniformly  with  the  depth,  while  the  elastic 
tension  of  steam  in  contact  with  water  increases  with  increas- 
ing heat  at  an  increasing  rate,  so  as  to  develop  a  logarithmic 
curve,  there  must  be  a  depth  at  which  the  tension  of  steam 
would  be  equal  to  the  downward  pressure,  and  that  at  that 
depth  would  be  found  the  limit  of  underground  water;  and  I 
expressed  this  conclusion  in  my  Elements  of  Geology,  page  99. 
Further  reflection  has  convinced  me  that  the  conclusion  is  un- 
warranted. Such  a  limit  would  undoubtedly  be  reached  if  the 
increase  of  tension  continued  to  follow  the  same  law  indefi- 
nitely. But  it  is  now  known  that  at  a  certain  temperature, 
called  the  critical  point,  steam  has  the  same  density  as  the 
water  from  which  it  is  formed.  At  this  point,  therefore,  it  may 

*  Of  the  two  causes  mentioned  above,  the  first  would  probably  produce  increase 
at  an  increasing  rate  and  put  the  place  of  density  equal  to  mean  density  deeper 
than  £  radius  down.  The  second  might  give  rise  to  any  kind  of  rate  according  to 
the  relative  amount  of  the  different  kinds  of  metals ;  but  not  improbably  to  a  de- 
creasing rate  and  put  the  place  of  mean  density  higher.  The  combination  of  these 
two  would  make  an  indeterminable  rate  ;  but  something  like  a  uniform  rate  is  as 
probable  as,  perhaps  more  probable  than,  any  other. 


274  THE    GENESIS    OF    ORE-DEPOSITS. 

be  regarded  as  either  steam  or  water  indifferently,  and  under 
the  slightest  change  of  temperature  it  takes  the  one  form  or  the 
other.  Beyond  this  point  it  is  no  longer  steam  in  contact  with 
water,  but  dry  steam,  which  we  know  follows  an  entirely  dif- 
ferent law.  Now  the  critical  point  of  water  is  about  700°  F. 
and  the  tension  of  steam  at  this  point  is  about  200  atmospheres. 
Taking  the  increase  of  underground  temperature  at  1°  for  53 
feet,  or  100°  per  mile,  the  temperature  of  700°  would  be  found 
at  the  depth  of  seven  miles.  But  the  pressure  of  a  water- 
column  there  would  be  about  1100  atmospheres.  The  tension 
has  not  yet  even  nearly  reached  the  pressure ;  and,  as  the  law 
changes  here,  it  would  seem  that  the  tension  would  never  over- 
take the  hydrostatic  pressure  at  all.  Therefore,  if  the  under- 
ground water  is  limited  at  all  in  its  downward  course,  as  is 
probably  the  case,  it  must  be  limited  in  some  other  way,  prob- 
ably by  increasing  compactness  of  material,  under  the  increas- 
ing pressure  of  superincumbent  rock,  which,  by  closing  up  the 
pores,  would  inhibit  further  penetration,  or  would  make  it  easier 
for  the  water  to  come  up  again  in  ascending  currents. 

I  think  we  may  reasonably  conclude,  therefore,  that  whether 
there  be  a  limit  to  underground  water  or  not,  it  is  certain  that 
below  a  certain  moderate  depth,  say  8  or  10  miles,  such  water 
cannot  be  circulating ;  for  beyond  this  the  compactness  of  rock 
under  superincumbent  pressure  would  be  such,  that  while  capil- 
larity and  weight  of  water-column  might  still  urge  further 
movement,  passages  sufficiently  open  to  allow  currents  of  circu- 
lation could  not  exist. 

We  may  assume,  then,  that  the  limit  of  circulating  water 
cannot  be  more  than  10  miles  in  depth.  Below  this,  water  may 
indeed  penetrate  by  capillarity  and  by  weight  of  its  own 
column,  but  such  water  does  not  enter  into  ordinary  circula- 
tion, although  it  may  come  up  in  volcanic  eruptions  and  indeed 
supply  the  force  of  such  eruptions.  Still,  below  this  again,  and 
even  to  the  very  center,  there  may  possibly  be  what  Fisher  calls 
constituent  water,  i.e.,  original  water  occluded  in  the  primal  fused 
magma  of  the  earth,  still  present  in  the  interior  and  coming  up 
in  volcanoes,  and  (according  to  him)  the  cause  of  their  erup- 
tions. If  there  be  such,  it  is  not  circulating  water  in  the  ordi- 
nary sense,  and  therefore  may  be  left  out  of  account  in  this  dis- 
cussion. 


THE   GENESIS    OP   ORE-DEPOSITS.  275 

Underground  water  may  be  conceived,  therefore,  as  existing 
in  three  possible  conditions,  but  more  and  more  doubtfully  in 
the  order  named  : 

1.  Circulating  meteoric  water.     This  of  course  is  certain. 
It  probably  extends  but  a  few  miles  (8  or  10)  below  the  sur- 
face. 

2.  Meteoric  water,  but  not  circulating.     The    existence  of 
this  is  probable.     I  have  been  accustomed  to  call  it  "  volcanic  " 
water,  because  it  is  a  probable  source  of  the  eruptive  force  of 
volcanoes. 

3.  Constituent   water,   originally   occluded   in   the   primal 
magma  of  the  incandescent  fused  earth,  and  still  occluded  in  the 
materials  of  the  interior.     This,  Fisher  thinks,  is  still  escaping, 
and  in  doing  so,  fuses  its  way  toward  the  surface,  and  finally 
emerges    in   volcanic    eruptions.     This,    of    course,    is   very 
doubtful. 

Of  these  three,  if  they  all  exist,  we  are  concerned,  I  believe, 
with  the  first  only. 

We  have  assumed  10  miles  as  the  limit  of  circulating  water, 
and  therefore  the  limit  of  depth  from  which  metals  may  be 
derived.  But  at  that  depth,  as  already  shown,  there  is  no 
"  barysphere  "  in  any  intelligible  sense  of  that  word.  For  the 
difference  in  density  and  in  metalliferousness  between  the  rocks 
there  and  those  at  the  surface  is  quite  inappreciable.  We 
have,  in  fact,  much  material  coming  up  from  this  very  region, 
and  therefore  know  its  density.  Our  more  basic  rocks  are 
indeed  far  denser  and  more  metalliferous  than  the  average  of 
that  region,  having  acquired  greater  density  by  differentiation 
from  an  average  magma  representing  that  region. 

I  believe,  therefore,  that  the  greater  abundance  of  metallic 
ores  in  solution  in  ascending  waters  is  the  result,  not  of  the 
greater  abundance  of  metals  in  their  lower  courses,  but  of  the 
greater  heat  which  they  take  up  in  that  part  of  their  course 
and  the  greater  pressure  to  which  they  have  been  subjected 
there.  Both  heat  and  pressure  greatly  increase  the  solvent 
power  of  water  upon  the  feebly  soluble  metallic  sulphides. 
Thus  heavily  freighted,  the  waters  lose,  in  ascending,  both  heat 
and  pressure,  and  therefore  deposit  abundantly  in  their  upward 
course.  In  a  word,  ascending  waters  are  rich  in  metallic  con- 
tents, not  because  they  have  traversed  a  barysphere,  but  because 

18 


276  THE   GENESIS    OF    ORE-DEPOSITS. 

they  have  traversed  a  thermosphere.  With  equal  heat  and  pres- 
sure, I  am  convinced,  they  would  get  as  much  metal  from  our 
more  basic  rocks  here  at  the  surface  as  they  now  do  from  the 
hypothetical  bary sphere.  These  ascending  waters  are  non- 
oxidizing,  not  because  they  have  never  seen  the  air,  i.e.,  are  not 
meteoric,  but  because  they  have  exhausted  their  oxidizing  power 
by  previous  oxidation  of  metals,  of  organic  matters,  and  other 
oxidable  substances  in  the  upper  parts  of  their  downward 

course. 

II. — YADOSE  vs.  DEEP  CIRCULATION. 

Again,  I  think,  Posepny  draws  much  too  sharp  a  distinction 
between  his  two  kinds  of  circulation;  not  indeed  as  to  their 
oxidizing  and  non-oxidizing  properties,  but  as  to  the  force  of 
circulation  in  the  two  cases  respectively.  In  his  anxiety  to 
distinguish  them  sharply,  he  speaks  as  if  the  forces  of  circula- 
tion in  the  two  cases  were  entirely  different,  being  gravity  or 
hydrostatic  pressure  in  the  one  case  and  capillarity  in  the  other. 
Now  nothing  can  be  more  certain  than  that  hydrostatic  pressure 
is  the  fundamental  cause  in  both  cases  alike ;  although  heat,  by 
lightening  the  ascending  column  and  thus  disturbing  the  hy- 
drostatic equilibrium,  is  the  immediately  determining  cause  in  the 
latter.  As  Mr.  Bickard,  in  the  discussion,  has  justly  pointed 
out,  the  effect  of  heat  in  the  underground  circulation  is  exactly 
like  its  effect  in  determining  circulation  in  a  system  of  house- 
warming  pipes. 

Again,  Posepny  lays  much  stress  on  capillarity  as  an  addi- 
tional force  urging  forward  the  circulation.  But  surely  this 
cannot  be  so.  Capillarity  is  indeed  a  powerful  force,  urging 
water  to  where  there  is  none,  but  an  equally  powerful  force 
fixing  it  where  it  is.  So  far  from  assisting,  it  powerfully  im- 
pedes circulation,  and,  where  it  is  strong  enough,  inhibits  it 
altogether.  Dry  clay  is  a  powerful  absorber  of  water,  but, 
when  once  wet,  it  becomes  impermeable  to  circulation. 

In  fact,  Posepny  sometimes  speaks  of  the  deep  barysphere 
circulation,  as  contrasted  with  the  vadose  circulation,  in  such 
terms  that  one  is  left  in  serious  doubt  whether  he  regards  the 
former  as  meteoric  water  at  all ;  and  yet  he  speaks  of  it  as  cir- 
culating. Sometimes  it  seems  as  if  he  regarded  his  vadose 
water  alone  as  meteoric  and  his  barysphere  water  as  some  other 
kind  of  water  coming  up  from  the  deep  interior  of  the  earth, 


THE    GENESIS    OF    ORE-DEPOSITS.  277 

like,  for  example,  the  constituent  water  of  Fisher.  Such  water, 
if  there  be  any  such,  might  indeed  be  conceived  as  coming  up 
from  a  metalliferous  barysphere,  such  as  he  supposes.  But  this 
would  be  escaping  water,  not  circulating  water.  If  he  means 
anything  like  this,  it  ought  to  be  distinctly  stated,  for  it  changes 
entirely  the  ground  of  discussion,  and  much  that  I  have  said 
above  would  be  wide  of  the  mark.  For  my  own  part,  unless 
we  adopt  Fisher's  view,  I  believe  that  we  never  have  any 
water  coming  up  which  has  not  previously  gone  down.  This  is 
what  is  meant  by  circulation,  but  I  cannot  think  Posepny  can 
mean  that  his  deep  circulating  water  is  not  meteoric ;  and  I 
therefore  say  nothing  more  on  this  head. 

III. — LEACHING  OF  WALL-ROCK. 

Again,  although  I  fully  agree  with  Posepny  and  his  brilliant 
expositor,  Dr.  Raymond,  that  crustification,  when  it  is  well  de- 
veloped, indicates  deposit  from  within,  by  ascending  waters  al- 
ready occupying  the  fissure,  and  not  by  laterally  incoming  water 
depositing  in  the  act  of  incoming  (in  the  manner  of  seepage- 
water  in  empty  cavities),  yet  I  cannot  agree  with  them  in  think- 
ing that  the  pressure  of  such  ascending  water  would  necessarily 
or  even  usually  prevent  the  incoming  of  lateral  currents  from 
the  wall-rock.  It  is  doubtless  true  that  the  ascending  water  in 
the  fissure  is  under  higher  pressure  than  precisely  similar  water 
on  the  outside ;  for,  in  addition  to  the  hydrostatic  pressure  de- 
termined by  the  height  of  the  outlet,  it  is  also  under  hydraulic 
pressure  in  proportion  to  the  velocity  of  the  upward  current. 
But  the  water  saturating  the  wall-rock  is  also,  of  course,  under 
heavy  hydrostatic  pressure.  And  when  we  remember  the  slow- 
ness of  the  ascending  current  (which  is  a  necessary  condition 
for  deposit),  and  therefore  the  slight  excess  of  the  pressure  over 
that  measured  by  the  height  of  its  outlet ;  and  when  we  re- 
member further  that  the  ascending  water  is  hot  while  the  wall- 
water  is  cooler,  and  therefore  denser,  we  may  well  doubt  whether 
the  pressure  of  the  ascending  or  the  lateral  waters  will  be  the 
greater,  and  therefore  whether  the  current  will  set  outward  or 
inward.  The  pressure  of  the  ascending  water  is  greater  by 
virtue  of  its  motion,  but  that  of  the  wall-rock  is  greater  by  vir- 
tue of  its  greater  density.  It  seems  not  unreasonable,  therefore, 
to  conclude  that  sometimes  and  in  some  places  the  current 


278  THE   GENESIS    OF    ORE-DEPOSITS. 

would  set  outward,  and  sometimes  and  in  some  places  it  would 
set  inward.  In  many  places,  doubtless,  the  wall-rock  is  not 
saturated.  In  such  places,  of  course,  the  current  would  set  out- 
ward by  capillarity,  as  well  as  by  pressure,  until  saturation  is 
reached.  Of  course,  also,  impediments  to  upward  flow,  brought 
about  by  filling  of  the  fissure  by  deposit  or  otherwise,  would 
increase  the  interior  pressure,  and  would  cause  an  upward  ram- 
ification and  outflow  in  many  places  at  the  surface. 

Although  the  analogy  is  by  no  means  perfect,  yet,  by  way  of 
illustration,  the  ascending  fissure-current,  with  its  freight  of  dis- 
solved matters  and  its  tributary  drainage  from  the  country-walls, 
may  be  roughly  compared  to  a  main  river  with  its  freight  of  sus- 
pended materials  and  its  lateral  tributaries.  In  such  a  stream, 
the  tributaries  usually  discharge  freely  into  the  main  river,  in- 
creasing in  volume,  though  perhaps  diminishing  its  percent- 
age of  freight;  but  sometimes,  by  the  greater  pressure  of  flood- 
waters,  the  main  stream  may  back  up  the  tributaries  until  equi- 
librium is  restored.  So  in  the  case  before  us,  the  main  ascend- 
ing fissure-stream,  with  its  freight  of  dissolved  matters,  usually 
receives  tributaries  from  the  wall-rock,  although,  by  defect  of 
pressure  of  the  latter  or  increased  pressure  of  the  former,  the 
main  current  may  overflow  into  the  wall-rock.  Again,  in  both 
cases,  the  percentage  of  freight  is  usually  greatest  in  the  main 
stream,  and  therefore  the  deposits  by  diminished  velocity  and 
carrying  power  in  the  one  case  and  by  diminished  heat  and 
pressure  and  solvent  power  in  the  other,  are  heaviest  there,  al- 
though sometimes  heavy  deposits  occur  also  in  the  back  waters. 
Again,  in  both  cases,  while  the  tributaries  increase  the  volume 
of  the  current,  they  usually  diminish  the  percentage  of  freight, 
although  sometimes  the  reverse  may  be  the  fact.  Finally,  as 
rivers,  when  obstructed  by  their  own  deposits,  may  reach  their 
final  destination  by  inverse  ramification  and  through  many 
mouths,  so  ascending  fissure-currents,  obstructed  by  their  own 
deposits,  may  branch  upward  and  reach  the  surface  by  many 
exits.  This,  however,  can  be  seen  only  in  ascending  currents 
still  depositing,  as  in  the  cases  of  Sulphur  Bank  and  Steamboat 
Springs.  In  most  cases  this  part  of  their  course  has  been 
carried  away  by  erosion. 

In  a  word,  there  seems  no  reasonable  doubt  that  while  usually 
the  main  deposits  have  been  brought  up  from  below,  yet  the 


THE   GENESIS    OF   ORE-DEPOSITS.  279 

tributaries  from  the  country-wall  do  contribute,  and  sometimes 
in  an  important  degree,  to  the  metallic  contents  of  the  veins. 
This  seems  well-nigh  proved  in  those  cases  given  by  Sandberger 
and  Becker,  in  which  analyses,  especially  selective  analyses,  find 
notable  quantities  of  the  required  metals  in  the  more  basic 
minerals  of  the  country  wall-rock.  To  discredit  the  obvious 
inferences  from  the  results  of  a  method  so  much  in  accord  with 
modern  science  and  substitute  a  roundabout  process  of  second- 
ary leachings  by  vadose  circulation  of  primary  impregnations 
derived  from  a  hypothetical  barysphere,  as  Posepny  does,  must 
be  regarded  as  a  return  to  the  speculative  methods  of  early 
writers.  Again,  in  cases  like  the  lead-ores  of  Missouri  and 
Wisconsin,  where  there  is  no  evidence  of  disturbance  or  of 
igneous  agency  of  any  kind,  is  it  not  more  rational  to  derive 
the  metals  from  the  wall-rock,  though  probably  from  its  deeper 
parts,  than  from  an  unknown  barysphere  ? 

IV. — A  MORE  COMPREHENSIVE  THEORY  NEEDED. 

In  conclusion,  I  cannot  but  think  that  the  views  brought  for- 
ward in  1883  in  my  paper  on  the  "  Genesis  of  Metalliferous 
Veins  "  (Am.  Jour,  of  Sti.,  vol.  xxvi.,  p.  1,  1883),  although  I 
would  perhaps  now  modify  them  slightly  on  some  points,  still 
represent  well  the  present  condition  of  science  on  this  subject. 
Those  who  have  read  that  paper  will  remember  that  it  is  an 
attempt  based  partly  on  my  own  investigations  of  the  phe- 
nomena of  metalliferous  vein-formation  now  going  on  at  Sul- 
phur Bank  and  at  Steamboat  Springs,  and  partly  on  a  general 
survey  of  the  whole  field,  to  embody  a  comprehensive  and 
rational  theory,  avoiding  extremes  on  both  hands.  In  it  I 
devoted  considerable  space  to  combating  the  extreme  lateral- 
secretion  views  of  Sandberger.  I  did  so  because,  on  account 
of  the  recent  appearance  and  signal  ability  of  his  treatise,  it 
seemed  likely  to  do  harm  by  carrying  scientific  opinion  too  far 
in  one  direction.  If  it  had  been  Posepny's  treatise  instead  of 
Sandberger's,  I  should  have  felt  equally  compelled  to  combat 
it,  and  on  the  same  ground.  Posepny  quotes  freely  from  my 
papers  on  "  Sulphur  Bank  "  and  on  "  Steamboat  Springs,"  but 
not  from  that  on  "  Genesis  of  Metalliferous  Veins."  Whether 
he  has  seen  it,  I  do  not  know. 

There  has  always  been,  and  still  is,  a  strong  tendency  to  ex- 


280  THE   GENESIS    OF   ORE-DEPOSITS. 

treme  views  on  this  subject.  On  the  one  hand,  ascensionists 
would  derive  all  metals  from  a  mysterious  metalliferous  region 
— a  "  barysphere,"  and  so  strong  is  their  advocacy  that  even 
when  analysis  finds  the  required  metals  in  notable  quantities 
in  the  wall-rock,  tHey  discredit  the  obvious  inference  by  sug- 
gesting a  secondary  leaching  of  materials  deposited  there  by 
primary  bary spheric  currents.  On  the  other  hand,  the  lateral- 
secretionists  would  derive  metals  not  from  ascending  currents 
at  all,  but  wholly  from  direct  secretion  from  the  immediate 
bounding-walls ;  and  so  strong  is  their  advocacy  that  even 
when  the  deposit  of  metals  from  hot  ascending  currents  is 
proved  by  direct  observation,  as  at  Sulphur  Bank  and  at  Steam- 
boat Springs,  they  seek  to  throw  discredit  on  the  obvious  infer- 
ence in  regard  to  all  metalliferous  veins,  by  giving  many  cases 
in  which  hot  springs  do  not  deposit  any  metals.  My  paper 
was  an  earnest  attempt  to  combine  what  is  true  in  each,  and 
thus  to  reconcile  these  extremes  by  a  more  comprehensive  view, 
which  explains  their  differences. 

According  to  my  view,  the  source  of  metals  is,  indeed,  on 
the  one  hand,  by  leaching,  but  not  by  lateral  secretion ;  on  the 
other  hand,  not  from  a  hypothetical  barysphere,  but  from  the 
wall-rock ;  though,  again,  not  from  all  points  alike,  but  mainly 
from  the  deepest  parts,  and  even  from  below  the  deepest  parts, 
of  sensible  fissures.  As  in  the  case  of  many  other  disputes,  I 
believe  both  sides  are  right  and  both  are  wrong.  Ascension- 
ists are  right  in  deriving  metals  mainly  by  ascending  currents 
from  great  depths,  but  wrong  in  imagining  these  depths  to  be 
an  exceptionally  metalliferous  barysphere.  They  are  wrong 
also  in  not  allowing  subordinate  contributions  by  lateral  cur- 
rents from  the  wall-rock  higher  up.  The  lateral-secretionists, 
on  the  other  hand,  are  right  in  deriving  metals  by  leaching, 
from  the  wall-rock,  but  wrong  in  not  making  the  main  source 
the  thermosphere. 

In  the  uncolored  light  of  a  more  comprehensive  view,  many 
of  the  difficulties  and  obscurities  of  the  subject  disappear. 

1.  Ore-deposits,  using  the  term  in  its  widest  sense,  may  take 
place  from  many  kinds  of  waters,  but  especially  from  alkaline 
solutions;  for  these  are  the  natural  solvents  of  metallic  sul- 
phides, and  metallic  sulphides  are  usually  the  original  form  of 
such  deposits. 


THE    GENESIS    OF    ORE-DEPOSITS.  281 

2.  They  may  take  place  from  waters  at  any  temperature 
and  pressure,  but  mainly  from  those  at  high  temperature  and 
under  heavy  pressure,  because,  on  account  of  their  great  solvent 
power,  such  waters  are  heavily  freighted  with  metals. 

3.  The  depositing  waters  may  be  moving  in  any  direction — 
up-coming,  horizontally  moving  or  even  sometimes  down-going, 
but  mainly  up-coming,  because  by  losing  heat  and  pressure  at 
every  step,  such  waters  are  sure  to  deposit  abundantly. 

4.  Deposits  may  take  place  in  any  kind  of  water-ways — in 
open  fissures,  in  incipient  fissures,  joints,  cracks,  and  even  in 
porous  sandstone,  but  especially  in  great  open  fissures,  because 
these  are  the  main  highways  of  ascending  waters  from  the 
greatest  depths.. 

5.  Deposits  may  be  found  in  many  regions  and  in  many 
kinds  of  rocks,  but  mainly  in  mountain-regions   and  in  meta- 
morphic  and  igneous  rocks,  because  the  therm osphere  is  nearer 
the  surface,  and  ready  access  thereto  through  great  fissures  is 
found  mostly  in  these  regions  and  in  these  rocks. 


282      SOME   PRINCIPLES   CONTROLLING   DEPOSITION   OF   ORES. 


Some  Principles  Controlling  the  Deposition  of  Ores.* 

BY  C.    R.    VAN   HISE,   MADISON,   WIS. 
(Washington  Meeting,  February,  1900.) 

PART  I. —GENERAL  PRINCIPLES. 

PAGE 

INTRODUCTION,     ,..,«.       .        .        .        *       -        ,        .        .        .  284 

THE  THREE  ZONES  OF  THE  LITHOSPHERE,    ...        ...        .  285 

Zone  of  fracture,     .        .        .        .        .        .         .        .        .        .         .  286 

Zone  of  flowage, .        .        .        .  286 

Factors  influencing  depth  at  which  flowage  occurs,          *  .     ,         .  287 

Zone  of  combined  fracture  and  flowage,          ....         .  288 

THE  WATER-CONTENT  AND  OPENINGS  IN  ROCKS, 291 

Condition  of  water  in  the  zone  of  fracture,    .         ;        v  '    V       .         ..  291 

The  openings  in  rocks, '  .        , !       .         .         .  293 

Size  and  number  of  openings,           ...         ....  295 

Ore-deposits  derived  from  zone  of  fracture, 300 

The  source  of  underground  water, .         .         ...        .         .         .  302 

The  cause  of  the  flowage  of  underground  water,    .         .        .        .         .  302 

Belts  of  underground  circulation,  ........  306 

Upper  belt  of  underground  circulation,  .....         .  306 

Lower  belt  of  underground  circulation,   ......  307 

Capacity  of  water  for  work  in  the  lower  belt  of  underground 

circulation,    ..........  308 

Movements  of  water  in  the  lower  belt  of  underground  circulation,  309 

The  preferential  use  by  water  of  large  channels,     ....  315 

PHYSICO-CHEMICAL  PRINCIPLES  CONTROLLING   THE  WORK  OF  UNDER- 
GROUND WATERS,       .        .        .        *   , 317 

Chemical  action,     .         ..........  318 

Underground  aqueous  solutions, 319 

The  relations  of  solution  and  temperature,       ....  320 

The  relations  of  solution  and  pressure,     .....  321 

Precipitation,  .        .         .  *'.        .         ...        .322 

Precipitation  by  change  in  temperature,  .....  323 

Precipitation  by  change  in  pressure,          .         .         .         .        .  324 

Precipitation  by  reactions  between  aqueous  solutions,       .        .  324 

Precipitation  by  reactions  between  liquid  solutions  and  solids,  325 
Precipitation  by  reactions  between    gases  and  solutions,  and 

solids, 326 

THE  GENERAL  GEOLOGICAL  WORK  OF  UNDERGROUND  WATERS,         *        .  326 
Division  of  the  zone  of  fracture  into  a  belt  of  weathering  and  a  belt  of 

cementation,        .         .        .         .        .         .        .         .         .                 .  327 

*  Published  by  permission  of   the  Director  of  the  United  States  Geological 
Survey. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.      283 


Migration  of  material  from  the  belt  of  weathering  to  the  belt  of  cemen- 
tation,           329 

PART  II.— APPLICATION  OF  PRINCIPLES  TO  ORE-DEPOSITS. 

THE  PRECIPITATION  OF  ORES  BY  ASCENDING  WATERS,        ....  339 

Precipitation  by  decrease  of  temperature  and  pressure,  ....  340 

Precipitation  by  mingling  of  solutions, 340 

Reactions  due  to  wall-rocks, 343 

General, 345 

The  compounds  deposited  by  ascending  waters,      .         .         .   ;    V        .  346 

Source  of  the  metals, 346 

Source  of  the  sulphur  of  sulphides,  .......  348 

Source  of  the  carbonic  acid  of  carbonates, 351 

General, 352 

THE  PRECIPITATION  or  ORES  BY  ASCENDING  AND  DESCENDING  WATERS 

COMBINED, *-     ,.        .        .         .  354 

THE  ASSOCIATION  OF  LEAD,  ZINC  AND  IRON  COMPOUNDS,     ....  357 

Facts  of  occurrence,        .        «        ,        «        .        .      ..  «        <•        .        •  358 

First  concentration,        .         .        .         .         .        V        .         .        .         .  359 

Sercond  concentration,     .         .........  359 

Galena,    .        «,     r. _ -.  .  >       :--v\*    .,,*>    .,.«/•   •         •         •         .360 

Sphalerite,       .         .        ,        ..,..,*      (  .         .         .         .  362 

Marcasite,        .        .        .,,    ".  '"'.'' 362 

General,         .        .        .        .V       .    ^  ;.        ^      n;   ^  i        .        .        .363 

THE  ASSOCIATION  OF  COPPER  AND  IRON  COMPOUNDS, 364 

THE  ASSOCIATION  OF  SILVER  AND  GOLD  WITH  THE  BASE  METALS,      .        .  368 

Silver,    .        .        .    '    .        .     /. 369 

Gold, 371 

CONCENTRATION  BY  REACTION  UPON  SULPHIDES  COMPARED  WITH  METAL- 
LURGICAL CONCENTRATION,         .        .               .              ,  . '......«.       •  376 

OTHER  REACTIONS  OF  DESCENDING  WATERS, 376 

SECOND  CONCENTRATION  FAVORED  BY  LARGE  OPENINGS  OF  THE  BELT  OF 

WEATHERING,     .                 378 

DEPTH  OF  THE  EFFECT  OF  DESCENDING  WATERS, 380 

ILLUSTRATIONS  OF  SECONDARY  ENRICHMENT  AND  DIMINUTION  OF  RICH- 
NESS WITH  DEPTH,     .        •        • 383 

General, 390 

THE  PRECIPITATION  OF  ORES  BY  DESCENDING  WATERS  ALONE,  .        .        .  393 

SPECIAL  FACTORS  AFFECTING  THE  CONCENTRATION  OF  ORES,      .        .        .  393 

Variations  in  porosity  and  structure,      .         .         .       V,'       .       V       .  393 

The  complexity  of  openings,   ........  394 

Impervious  strata  at  various  depths,         .         .....  396 

Pitching  troughs  and  arches, 405 

Pre-existing  channels  and  replacements, 413 

Character  of  the  topography, 416 

Effect  of  the  vertical  element, 416 

Effect  of  the  horizontal  element, 417 

Physical  revolutions,      ..........  419 

General, 420 

ORE-CHUTES,         .                 421 

THE  CLASSIFICATION  OF  ORE-DEPOSITS, 427 


284     SOME   PRINCIPLES   CONTROLLING    DEPOSITION    OF    ORES. 

PART  L— GEKERAL  PRINCIPLES. 
INTRODUCTION. 

THE  following  paper  upon  the  principles  controlling  the 
deposition  of  ores  is  adapted  from  a  treatise  on  Metamor- 
phism,  to  be  published  hereafter  as  a  Monograph  of  the  United 
States  Geological  Survey.  In  the  present  paper  the  argument 
can  be  made  only  in  outline.  The  argument  is  especially  frag- 
mentary in  the  treatment  of  the  general  principles  controlling 
the  circulation  of  underground  water. 

It  will  be  held  in  this  paper  that  the  deposition  of  most  ores 
is  but  a  special  case  of  the  general  work  of  groundwaters,  of 
exceptional  interest  to  man.  In  order  to  understand  the 
special  problem,  it  is  necessary  to  have  a  profound  knowledge 
of  the  general  principles  controlling  the  circulation  and  work 
of  groundwaters.  In  the  treatise  from  which  this  work  is 
adapted  I  have  attempted  to  treat  this  subject  more  fully  and 
broadly  than  has  heretofore  been  done.  From  this  treatise  so 
much  is  abstracted  as  seems  absolutely  necessary  in  order  to 
understand  the  special  application  of  the  work  of  groundwaters 
to  the  genesis  of  ore-deposits.  Where  points  are  not  covered 
with  sufficient  fullness,  I  beg  the  reader  to  suspend  judgment 
until  he  sees  the  full  treatise. 

In  the  treatise,  as  well  as  in  the  following  paper,  I  have  of 
course  drawn  upon  .the  knowledge  contained  in  the  writings 
of  all  previous  workers.  No  general  treatise  upon  a  broad 
subject  is  the  work  of  a  single  man.  It  is  the  conjoint  product 
of  all  previous  workers  and  its  writer.  In  the  following  dis- 
cussion of  ore-deposits  I  am  indebted  to  all  who  have  contrib- 
uted ideas  to  this  subject,  from  the  great  Bischof  to  Sandberger 
and  Posepny.  I  have  tried  to  give  full  credit  to  all  by  numerous 
references;  but  I  cannot  be  sure  that  I  have  done  full  justice  in 
every  case.  A  comparison  with  the  writings  of  others  will  show 
that  I  am  in  accord  with  Prof.  Joseph  Le  Conte  upon  more 
points  than  with  any  one  else.* 

Ore-deposits  may  be  divided  into  three  groups,    viz. :  (A) 

*  See  discussion  in  this* volume,  page  270.  "On  the  Genesis  of  Metalliferous 
Veins,"  by  Jos.  Le  Conte  :  Am.  Journ.  £ci.,«3d  Series,  voL  xxvi.,  1883,  p.  I 
et  seq. 


.SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       285 

ores  of  direct  igneous  origin,  (B)  ores  which  are  the  direct 
result  of  the  processes  of  sedimentation,  and  (C)  ores  which 
are  deposited  by  underground  water. 

Ore-deposits  of  direct  igneous  origin  are  probably  of  limited 
extent.  Certain  very  basic  igneous  rocks  have  been  worked  as 
iron-ores.  In  Norway  are  sulphide  ores  of  various  metals 
which  Yogt*  holds  to  be  a  direct  segregation  from  a  magma. 
Emmonsf  has  also  favored  the  idea  of  at  least  a  first  concentra- 
tion of  the  metallic  contents  of  ore  by  processes  of  differentia- 
tion from  igneous  rocks,  more  particularly  basic  ones.  In 
many  cases  where  ore-deposits,  and  especially  sulphides  are 
supposed  to  be  igneous,  the  question  may  pertinently  be  asked 
as  to  how  far  aqueous  agencies  have  worked  in  connection  with 
the  igneous  agencies.  I  suspect,  in  most  cases,  that  even  if  a 
first  concentration  has  been  accomplished  by  magmatic  differ- 
entiation, that  a  second  and  more  important  concentration  has 
been  performed  by  underground  waters,  and  this  position  I  un- 
derstand Emmons  also  to  hold.  Upon  the  question  as  to  how 
far  some  ore-deposits  are  the  direct  processes  of  igneous  agen- 
cies I  do  not  propose  here  to  enter. 

To  a  limited  extent  ores  are  also  the  direct  result  of  pro- 
cesses of  sedimentation.  As  an  instance  of  such  ores  may  be 
mentioned  some  placer  deposits.  Possibly  some  ores  are  due 
to  sublimation. 

However,  in  so  far  as  ores  are  of  igneous  origin,  or  are  the 
direct  result  of  the  processes  of  sedimentation,  or  are  the  results 
of  sublimation,  they  are  excluded  from  the  scope  of  the  present 
paper.  I  intend  here  to  consider  only  the  third  group  of  ores, 
— those  produced  through  the  agency  of  underground  waters. 

My  first  and  fundamental  premise  is  that  the  greater  number  of 
ore-deposits  are  the  result  of  the  work  of  underground  water. 

THE  THREE  ZONES  OF  THE  LITHOSPHERE. 
In  another  placej  I  have  shown  that  the  outer  part  of  the 
crust  of  the  earth  may  be  divided  into  three  zones,  depending 

*  J.  H.  L.  Vogt:  Zeitschr.  fur  prakt.  Geol.,  Jan.  and  Apr.,  1893;  Oct.,  1894; 
Apr.,  Sept.,  Nov.,  Dec.,  1895. 

f  Trans.  Am.  Inst.  Min.  Eny.,  vol.  xxii.,  pp.  53-95.  "The  Mines  of  Ouster 
County,  Oolorado,"  by  S.  F.  Emmons  :  17th  Ann.  Rept.  U.  8.  Geol.  Surv.,  part  ii., 
1895-96,  pp.  470-472. 

J  "Principles  of  North  American  Pre-Cambrian  Geology,"  by  0.  K.  Van 
Hise,  16th  Ann.  Rep.  U.  S.  Geol.  Surv.  for  1894-5,  pt.  i.,  p.  589  etseq.,  1896. 


286      SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF   ORES. 

upon  the  character  of  its  deformation  :  an  upper  zone  of  frac- 
ture, a  lower  zone  of  rock  flowage,  and  a  middle  zone  of  com- 
bined fracture  and  flowage. 

Zone  of  Fracture. 

The  zone  of  fracture  is  that  near  the  surface.  In  this  zone 
the  rocks  are  not  deformed  mainly  by  flowage,  but  by  fracture. 
They  are  adjusted  to  their  new  positions  mainly  by  rupture  and 
differential  movements  between  the  separated  parts.  When 
rocks  are  deformed  in  the  zone  of  fracture  the  ruptures  which 
occur  are  those  of  faulting,  jointing,  differential  movements  be- 
tween the  layers  (or  accommodation),  fissility,  and  brecciation. 
The  so-called  folds  in  the  zone  of  fracture  are  chiefly  the  result 
of  numerous  parallel  joint-fractures  across  the  strata  with  slight 
displacements  at  the  joints,  giving  each  block  a  slightly  differ- 
ent position  from  the  previous  one,  and  thus  as  a  whole  mak- 
ing a  fold.  For  instance,  the  folds  of  the  rigid  rocks  in  the 
Alleghenies  are  not  in  the  main  true  flexures,  but  a  series  of 
slightly  displaced  blocks. 

Zone  of  Flowage. 

In  the  zone  of  rock-flowage  the  deformation  is  by  granulation 
or  recrystallization,  no  openings  being  produced,  or  at  least 
none  except  those  of  microscopic  size.*  This  conclusion  rests 
upon  arguments  which  cannot  here  be  fully  repeated.  How- 
ever, it  may  be  said  in  passing  that  the  conclusion  that  a  zone 
of  rock-flowage  exists  at  moderate  depth  is  based,  first,  upon 
deduction  from  known  physical  principles  as  to  the  behavior 
of  solid  bodies  under  pressure,  and  second,  upon  observation. 
It  is  well  known  that  when  a  rigid  body,  such  as  rock,  is  sub- 
jected to  stress  greater  than  its  ultimate  strength,  it  must  rup- 
ture or  flow.  If  a  rock  be  subjected  to  a  stress  in  a  single 
direction  greater  than  its  ultimate  strength  in  that  direction, 
and  the  rock  is  not  under  pressure  in  other  directions,  rupture 
occurs.  However,  if  we  suppose  that  the  rock  be  subjected  to 
stresses  greater  than  the  ultimate  strength  of  the  rock  in  all 
directions,  and  that  the  difference  in  the  stresses  in  different 
directions  is  greater  than  the  ultimate  strength  of  the  rock 

*  "  Principles,"  cit.,  p.  594,  et  seg. 


SOME   PRINCIPLES   CONTROLLING   DEPOSITION    OF    ORES.      287 

under  the  conditions  in  which  it  exists,  then  if  openings  could 
be  produced  by  a  rupture,  they  would  almost  immediately  be 
closed  by  pressure.  In  other  words,  at  a  certain  depth  below 
the  surface  of  the  earth,  if  we  could  suppose  that  cracks  and 
crevices  are  formed  by  the  deformation  to  which  the  rocks  are 
subjected,  the  pressures  in  all  directions  being  greater  than  the 
ultimate  strength  of  the  rock,  these  cracks  and  crevices  would 
be  almost  immediately  closed. 

Since  this  conclusion  was  reached,  Adams  has  actually  de- 
formed marble  under  the  conditions  supposed  to  exist  at  mod- 
erate depth  below  the  earth,  with  the  result  that  the  rock 
changed  its  form  without  rupture  and  with  no  perceptible 
openings  or  cracks.* 

Before  the  above  inductive  reasoning  or  Adams'  experiment 
was  made,  I  had  become  convinced  from  observation  that  at 
moderate  depth  rocks  are  deformed  with  fracture  and  differen- 
tial movements  between  the  solid  particles  (granulation),  and  by 
continuous  solution  and  redeposition  by  underground  water 
(recrystallizatiori).-\  It  was  calculated  that  for  all  but  the  very 
strongest  rocks,  flowage  must  begin  at  a  depth  not  greater  than 
12,000  meters,!  for  at  this  level  the  weight  of  the  superincum- 
bent mass  is  greater  than  the  ultimate  strength  of  the  rocks. 

Factors  Influencing  Depth  at  Which  Flowage  Occurs. — In  the 
case  of  anticlinal  arches  a  portion  of  the  load  may  be  removed 
by  the  supporting  limbs,  and  thus  the  depth  of  the  level  at  which 
the  zone  of  flowage  occurs  beneath  the  arch  be  theoretically 
somewhat  increased.  However,  it  is  highly  probable  that  lateral 
stresses  and  increased  temperature  which  always  accompany 
rapid  deformation,  more  than  compensate  for  any  removal  of 
load.  Time  is  another  important  factor.  It  is  well  known  that 
a  stress  which  in  a  short  time  is  insufficient  to  rupture  material 
may,  if  long  continued,  result  in  its  deformation  by  flowage. 
The  geologist  has  this  factor,  time,  to  a  larger  extent  than  scien- 
tists in  any  other  subject,  and  it  is  a  factor  which  he  has  con- 

*  Experiments  in  the  flow  of  rocks  are  still  being  made  at  McGill  University 
by  Frank  D.  Adams.  A  preliminary  account  was  presented  to  the  Geol.  Soc. 
Am.,  Montreal  meeting,  1897.  This  is  summarized  in  "  Science,"  vol.  vii.,  1898, 
pp.  82-83. 

f  " Metamorphism of  Eocks  and  Kock  Flowage,"  by  C.  B.  Van  Hise.  Bull. G. 
S.  A.,  vol.  ix.,  1898,  pp.  295-313,  318-326. 

J  "  Principles,  "ct<.,  p.  592. 


288      SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

stantly  to  keep  in  mind.  How  important  this  factor  is  may  be 
illustrated  by  the  deformations  of  rocks  as  result  of  very 
moderate  long-continued  pressures.  In  some  cases,  in  ceme- 
teries, marble  slabs  have  been  placed  horizontally  and  suspended 
at  the  ends.  In  the  course  of  a  score  or  more  of  years  such 
slabs  are  found  to  have  sagged  in  the  middle  a  very  consider- 
able amount.  If  the  slabs  had  at  the  outset  been  bent  to  this 
extent  they  would  have  undoubtedly  been  ruptured.  The 
change  in  form  is  only  possible  by  rock  flowage,  either  through 
a  differential  movement  of  the  solid  particles  with  reference 
to  one  another  or  by  solution  and  redeposition,  i.e.,  recrystal- 
lization,  or  the  two  combined.  The  consideration  of  time  leads 
me  to  believe  that  the  limit  of  10,000  to  12,000  meters  placed 
as  the  level  at  which  flowage  of  the  strong  rocks  must  occur  is 
probably  too  great,  and  observations  upon  deformation  in  the 
cores  of  mountain  masses  which  have  been  deeply  denuded  con- 
firm this  conclusion.  Rocks,  even  of  the  strongest  kind,  have 
in  many  instances  been  deformed  by  flowage  rather  than  by 
fracture,  when  at  depths  much  less  than  10,000  meters. 

Other  factors,  such  as  igneous  intrusions  or  orogenic  move- 
ments, increase  the  heat  and  pressure  acting  on  the  rock,  and 
thus  tend  to  diminish  the  depth  at  which  flowage  occurs. 

If  this  reasoning  is  correct,  it  follows  that  all  fissures  must 
disappear  at  some  depth,  and  that  the  maximum  depth  is 
limited  by  the  depth  of  the  zone  of  fracture  for  the  strongest 
rocks. 

Zone  of  Combined  Fracture  and  Flowage. 

There  is  a  zone  of  combined  fracture  and  flowage  below  the 
zone  of  fracture,  because  rocks  have  varying  strengths,  because 
there  is  great  variation  in  the  rapidity  of  deformation,  in  the 
temperature  at  which  the  deformation  occurs,  in  the  moisture 
present,  and  in  various  other  factors.  A  weak  rock,  for  instance 
a  shale,  may  be  deformed  by  flowage  at  a  much  less  depth  than 
a  strong  rock,  such  as  a  granite.  Thus  the  belt  of  combined 
fracture  and  flowage  is  of  considerable  thickness,  possibly  as 
thick  as  5000  meters.  In  this  zone  we  have  all  combinations 
of  the  phenomena  of  fracture  in  the  various  ways  above  men- 
tioned, and  of  flowage  by  granulation  and  recrystallization. 

It  is  highly  probable  that  the  openings  of  the  zone  of  fracture 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION   OF    ORES.      289 

gradually  decrease  in  size  as  depth,  increases,  until  in  the  zone 
of  flowage  the  openings  are,  as  already  explained,  microscopic 
or  non-existent.  If  a  gradation  such  as  indicated  exists,  it  is  a 
necessary  corollary  that  the  deformations  of  the  zone  of  frac- 
ture must  have  their  equivalents  in  the  deeper  seated  zone  of 
flowage  and  flexure.  This  point  I  have  fully  developed  in  other 
places.*  It  is  explained  that  in  depth  faults  are  replaced  by 
flexures,  and  that  any  deformation  of  a  large  mass  of  a  given 
rock  from  one  form  to  another  by  fracturing  may  be  paralleled 
by  similar  changes  of  form  in  the  zone  of  flowage,  the  result 
being  there  accomplished  by  granulation  of  the  mineral  par- 
ticles or  by  recrystallization,  or  by  both. 

It  might  be  thought  that  the  above  general  statement  is  a 
deduction  which  cannot  be  confirmed  by  observation,  but  such 
is  not  the  case.  Many  rocks  which  have  been  deformed  in  the 
zone  of  flowage  or  in  the  zone  of  combined  fracture  and  flow- 
age,  as  a  consequence  of  denudation  have  reached  the  surface, 
and  one  is  able  to  observe  all  the  transition  phenomena  of  de- 
formation between  the  zones  of  fracture  and  flowage.  These 
I  have  somewhat  fully  described  in  another  place. f  An  excel- 
lent illustration  of  the  deformation  of  a  rock  mainly  by  flowage, 
but  in  a  subordinate  way  by  fracture,  is  the  Berlin  rhyolite- 
gneiss,  described  by  Samuel  Weidman.J  The  formation  of 
this  rock  was  mainly  that  of  recrystallization,  but  many  of  the 
mineral  particles  were  granulated.  Also  many  minute  joint 
crevices  were  formed  which  were  subsequently  filled  by  cemen- 
tation. 

It  follows  from  the  above  reasoning  that  fissures  may  dis- 
appear at  different  depths  below.  Where  there  are  fractures 
with  large  displacements,  fissures  are  likely  to  extend  to  very 
considerable  depths.  In  proportion  as  the  displacements  are 
small,  the  fissures  are  likely  to  disappear  below  at  less  depths. 
Furthermore,  as  has  already  been  explained,  certain  rocks  are 
deformed  by  flowage  at  a  much  less  depth  than  are  other 
rocks.  Therefore,  in  a  region  in  which  there  is  a  great  shale 

*  "Principles,"  cit.,  p.  676;  "  Metamorphism,"  cit.,  pp.  313-318. 

f  "Principles,"  aL,  pp.  601-603;  "  Metamorphism,"  cit.,  pp.  312-313. 

J  "  A  Contribution  to  the  Geology  of  the  Pre-Cambrian  Igneous  Kocks  of  the 
Fox  Kiver  Valley,  Wisconsin,"  by  S.  Weidman.  Bull.  Wis.  Geol.  and  Nat.  Hist. 
Surv.,No.  III.,  pt.  2,  1898. 


290       SOME   PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

or  slate  formation  at  a  moderate  depth,  a  strong  fissure  in  more 
brittle  rocks  at  the  surface  may  disappear  as  it  encounters  the 
shale  formation,  being  replaced  there  by  a  flexure.  I  have 
little  doubt  that  considerable  fissures  thus  disappear  at  a  depth 
less  than  1000  meters. 

Illustrations  of  the  disappearance  of  fissures  with  depth  are 
found  at  various  places.  In  the  gold  belt  of  the  Sierra  Nevadas, 
Lindgren*  says  it  is  "  an  incontestable  fact  that  many  small 
veins  close  up  in  depth." 

Not  only  may  fissures  die  out  below,  but  fissures  may  disap- 
pear above,  the  fault  along  the  fissures  being  replaced  by  a 
flexure  in  the  overlying  stratum,  wrhich  yields  by  flowage. 
This  is  beautifully  illustrated  by  the  Enterprise  mine,  of 
Rico,  Col.,  described  by  Rickard,f  where  faulted  fissures  in 
sandstone  and  limestone  disappear  above,  at  the  place  where 
shale  is  encountered,  the  shale  accommodating  itself  to  the  frac- 
tures below  by  monoclinal  flexures.  (See  Fig.  9,  p.  409.) 

The  marked  effect  which  the  character  of  the  country  rock 
may  have  upon  the  nature  of  a  fissure  is  well  illustrated  in  the 
Cripple  Creek  district,  where,  according  to  Penrose,J  the  fis- 
sures in  the  hard  rocks  are  sharp,  clean-cut  breaks,  while  in 
the  soft  rocks  they  are  ordinarily  a  series  of  very  small  cracks, 
constituting  a  displacement  of  a  kind  which  I  call  a  distributive 
fault.  Well  illustrating  this  are  mines  which  are  partly  in  hard 
and  partly  in  soft  rock.  "  The  vein  on  which  the  Buena  Yista, 
Lee,  Smuggler,  and  Victor  mines  are  located  occupies  a  sharp, 
clean-cut  fissure,  partly  in  the  massive  rock  and  partly  in  the 
hard  breccia;  but  when  it  passes  into  the  soft,  tufaceous 
breccia  on  the  east  slope  of  Bull  Hill  the  fissure  is  represented 
only  by  faint  cracks  occupied  by  no  vein  of  importance.  In 
this  case  the  force  which  caused  the  fissure  overcame  the  co- 
hesion of  the  harder  rock  sufficiently  to  make  a  clean  break, 
but  in  the  more  plastic  rock  it  overcame  cohesion  only  to  the 


*  "The  Gold-Quartz  Veins  of  Nevada  City  and  Grass  Valley,  California,"  by 
Waldenlar  Lindgren,  17 th  Ann.  Eept.  U.  S.  Geol.  Surv.,  pt.  ii.,  1895-96, 
p.  162. 

f  "The  Enterprise  Mine,  Kico,  Col.,"  by  T.  A.  Kickard,  Trans.  Am.  Inst. 
Min.  Engineers,  vol.  xxvi.,  1897,  pp.  906-980. 

$  "Mining  Geology  of  the  Cripple  Creek  District,"  by  K.  A.  F.  Penrose,  Jr. 
IQthAnn.  Rept.  U.  S.  Geol.  Surv.,  pt.  ii.,  1894-95,  p.  144. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       291 

extent  of  causing  a  series  of  faint  fractures  without  any  one 
well-defined  break."* 

This  point  of  transition  between  the  zone  of  fracture  and  the 
zone  of  flowage  and  the  dying  out  of  fissures  below  is  dwelt 
upon  in  order  to  exclude  the  hypothesis  of  filling  of  fissures 
from  the  bottom.  If  fissures  gradually  decrease  in  size  and 
finally  die  out,  the  streams  which  make  their  way  into  the  fis- 
sure must  enter  from  the  side  or  from  above.  For  further  de- 
velopment of  this  point,  see  pp.  335-337. 

In  closing  the  subject  it  may  be  said  that  in  all  cases  where 
rocks  have  been  deformed  in  the  zone  of  rock  flowage,  or  in 
the  zone  of  combined  fracture  and  flowage,  and  are  now  at  the 
surface,  there  will  be  superimposed,  upon  the  effects  of  the 
deep-seated  deformation,  the  deformation  by  fracture,  resulting 
from  earth  movements  during  the  time  the  rock  is  slowly  mi- 
grating through  the  zone  of  fracture  to  the  surface. 

THE  WATER-CONTENT  AND  OPENINGS  IN  ROCKS. 

Since  the  ore-deposits  considered  in  this  paper  are  the  work 
of  underground  water,  and  since  the  flowage  of  underground 
water  is  mainly  through  the  openings  in  rocks,  it  is  necessary 
to  consider  the  condition  of  the  water  in  the  openings  and  the 
character  of  the  openings  which  may  occur  in  rocks. 

As  to  the  content  of  water  the  zone  of  fracture  may  be  di- 
vided into  two  belts,  an  upper  belt  above  the  level  of  ground- 
water  called  the  belt  of  weathering  and  a  lower  belt  below  the 
level  of  groundwater  called  the  belt  of  saturation.  Above  the 
level  of  groundwater  the  openings  in  the  rocks  are  ordinarily 
only  partly  filled  with  liquid.  Under  different  conditions,  which 
need  not  here  be  discussed,  the  water  in  the  openings  varies 
from  an  exceedingly  small  fraction  of  that  required  to  fill  the 
openings,  to  saturation. 

Condition  of  Water  in  the  Zone  of  Fracture. 

In  the  belt  of  saturation,  from  the  level  of  groundwater  to 

its  base,  if  it  be  limited  to  a  depth  of  10,000  meters,  the  H2O  is 

in  liquid  form,  as  water.      The  water  is,  however,  for  much  of 

the  belt  superheated.     If  the  increment  of  increase  of  tempera- 

*  Loc.  tit.,  p.  144. 
19 


292       SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF   ORES. 


ture  be  taken  as  1°  C.  for  every  30  meters,  the  critical  tem- 
perature of  water,  364°  C.,  would  be  found  at  a  depth  of  10,920 
meters.  At  any  given  place  the  water  is  subject  to  the  pressure 
of  the  superincumbent  column.  The  question,  whether  hydro- 
static pressure  increases  at  a  rate  sufficient  to  prevent  the  vapor- 
ization of  the  water,  must  be  answered. 

If  the  temperature  of  the  water  were  100°  C.,  or  just  at  the 
boiling-point  at  the  surface  of  the  earth,  the  most  unfavorable 
assumption  to  holding  the  water  as  a  liquid  in  the  zone  of 
fracture,  it  would  still  be  true  that  the  water  would  be  in  the 
form  of  liquid  in  this  zone,  as  is  shown  by  the  following 
table  based  upon  this  supposition,  column  (1)  being  tempera- 
tures, column  (2)  being  pressures  necessary  to  hold  H20  as  a 
liquid  at  these  temperatures,  column  (3)  being  depth  in  meters 
at  which  the  pressures  would  be  produced,  column  (4)  being 
the  depth  which  would  be  required  to  produce  the  temperatures 
on  the  supposition  that  the  increment  of  the  increase  of  tem- 
perature is  1°  C.  for  every  30  meters,  and  column  (5)  being  the 
actual  temperatures  which  exist  upon  this  supposition  at  the 
depths  represented  by  column  (3) : 


(1.) 

Temperatures 
(100°  C.  at  Sur- 
face). 

(2.) 
Pressures  Corre- 
sponding to 
Temperature  of 
Col.  1. 

(3.) 
Depth  Necessary 
to  Produce 
Pressure  of  Col.  2. 

(4.) 
Depth  Necessary 
to  Produce 
Temperature  of 
Col.  1. 

(5.) 
Temperatures  Actu- 
ally Existing  at 
Pressures  and 
Depths  of  Cols.  2 
and  3. 

Deg.  C. 

Atm. 

Meters. 

Meters. 

Deg.  C. 

120 

2 

20 

600 

100.66 

180 

10 

100 

2,400 

103.33 

225 

25 

250 

3,750 

108.33 

265 

51 

510 

4,950 

117.00 

310 

99 

990 

6,300 

133.00 

340 

148 

1,480 

7,200 

149.33 

365 

205.5 

2,055 

7,950 

168.33 

From  this  table  it  will  be  seen  that  the  hydrostatic  pressure 
at  various  depths  is  far  in  excess  of  that  required  to  hold  the 
water  in  the  form  of  a  liquid ;  or,  looked  at  in  another  way,  for 
any  given  depth  the  temperature  is  not  sufficiently  high  to  allow 
the  water  at  that  depth  and  pressure  to  exist  in  the  form  of  a 
gas. 

Therefore,  where  the  increase  of  temperature  is  normal,  the 
pressure  at  any  point  down  to  the  level  at  which  the  critical 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       293 

temperature  of  water  is  met  is  clearly  much  more  than  adequate 
to  prevent  the  water  from  changing  to  steam.  Where  magma 
is  intruded  in  the  lithosphere,  the  temperature  may  become  so 
high  that  this  statement  will  not  hold.  This,  however,  is  the 
exceptional,  not  the  usual,  case.  Furthermore,  it  is  conceivable 
that  as  result  of  deformation  itself  the  temperature  of  the  rocks 
might  rise  so  high  as  to  convert  the  water  present  into  the  form 
of  steam.  This  possibility  will  not  be  discussed.  However,  it  is 
believed  to  be  probable  from  investigations  upon  metamorphism 
that  this  condition  of  affairs  rarely  if  ever  obtains,  since,  as  I 
have  elsewhere  explained,  long  before  the  critical  temperature 
of  water  is  reached,  solution  and  deposition  of  rock  material,  or 
recrystallization,  readily  takes  place,  and  in  this  change  the 
work  converted  into  heat  is  far  less  than  in  mechanical  granu- 
lation.* 

The  Openings  in  Rocks. 

The  openings  in  rocks  include  (1)  those  which  are  of  great 
length  and  depth,  as  compared  with  their  width,  and  thus  are 
essentially  flat  parallelepipeds ;  (2)  those  in  which  the  dimen- 
sions of  the  cross-sections  of  the  openings  are  approximately  the 
same,  and  therefore  resemble  tubes  of  various  kinds,  and  (3) 
irregular  openings. 

(1)  The  openings  of.  the  first  kind  are  those  of  faults,  of 
joints,  of  fissility,  and  of  bedding  partings.  The  openings  of 
this  class  are  likely  to  be  continuous  for  considerable  distances. 
This  is  true  to  the  largest  extent  of  fault  openings,  is  true  to  a 
less  extent  of  joint  openings  and  bedding  partings,  and  to  a  still 
less  extent  of  the  openings  of  fissility.  It  is  recognized  that 
many  of  the  fissures  are  exceedingly  complex.  They  are,  in- 
deed, in  many  instances,  a  series  of  parallel  or  intersecting  frac- 
tures, forming  a  zone  of  brecciation.  However,  for  such  a  zone, 
as  a  whole, -the  statement  still  holds  that  the  openings  have  great 
length  and  depth  as  compared  with  their  width.  In  position, 
the  joint-,  fault-,  and  fissility-openings  ordinarily  have  an  im- 
portant vertical  element,  or  at  least  traverse  the  beds.  Frequently 
they  are  nearly  vertical,  or  traverse  layers  of  formations  at  right 
angles.  In  consequence  of  this,  they  are  very  important  factors 

*   "  Metamorphism  of  Kocks  and  Kock  Flo  wage,"  by  C.  K.  Van  Hise,  Bull.  G. 
S.  A.,  vol.  ix.,  1898,  pp.  310-311,  313-318. 


294       SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

in  the  flowage  of  underground  water.  Relatively  pervious  for- 
mations separated  by  impervious  formations  may  be  thus  con- 
nected. Pervious  formations  overlain  by  impervious  formations 
may  be  connected  with  the  surface.  Bedding-partings  are 
parallel  to  the  layers.  Since  underground  waters  very  fre- 
quently follow  formations,  the  bedding-partings,  which  extend 
long  distances,  become  very  important  factors  in  the  promotion 
of  flowage  parallel  to  the  formations.  This  is  especially  true 
of  the  contact  of  formations  of  different  character.  These  con- 
tacts are  places  of  maximum  differential  movements,  of  conse- 
quent complex  fracturing,  and  therefore  of  important  openings 
and  large  circulation. 

(2)  The  spaces  of  the  second  class  are  those  of  the  mechani- 
cal sediments,  including  conglomerates,  sandstones,  soils,  tuffs, 
etc.     The  openings  of  mechanical  sediments  have  a  strong  ten- 
dency to  a  definite  form,  and  are   continuous.     The  forms  of 
these  openings  have  been  fully  discussed  by  Slichter.*     The 
openings  alternately  narrow  and  widen.     At  their  wider  parts 
their  sections  are  roughly  polygonal  ,  the  polygons  having  more 
than  three  sides,  and  these  are  curved.  At  their  narrowest  places, 
the  cross-sections  of  the  openings  approximate  to  triangles,  and 
where  the  grains  are  of  equal  size,  the  triangles  are  equilateral. 
The  form  of  the  tubes  at  their  minimum  cross-section  is  due  to 
the  contact  of  three  grains  in  a  plane,  the  space  between  which 
is  nearly  triangular. 

(3)  Irregular  openings  are  those  of  the  vesicular  lavas  and 
the  irregular  fractures  of  the  rocks.     They  are  in  part  con- 
tinuous and  in  part  discontinuous.     In  rocks  where  the  open- 
ings are  exceedingly  irregular  in  form,  the  flowage  of  water  is 
limited  to  the  continuous  openings,  however  small  they  may  be. 

Openings  of  any  of  the  above  classes,  whether  a  result  of 
deformation  or  produced  by  original  sedimentation  or  formed 
in  connection  with  volcanic  action,  may  be  enlarged  by  solution. 
Indeed,  this  will  be  the  case  wherever  the  processes  of  solution 
more  than  counterbalance  the  processes  of  precipitation.  It  is 
later  explained  that  this  is  the  more  likely  to  occur  with  down- 
ward moving  water  than  with  upward  moving  water.  Since 


*  "Theoretical   Investigation   of   the  Motion  of  Ground  Waters/'    by  C.  S. 
Slichter,  IQth  Ann.  Kept.  U.  S.  Geol.  Surv.,  for  1897-98,  pt.  ii.,  pp.  305-323. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION   OF    ORES.       295 

downward  moving  waters  are  dominant  above  the  level  of 
groundwater  and  prominent  in  the  upper  part  of  the  belt  of 
saturation,  it  is  in  this  area  that  openings  are  most  frequently 
enlarged  by  solution.  (See  pp.  327-329,413.)  It  has  been  argued 
by  Posepny*  that  openings  serving  as  channels  for  underground 
water  may  be  wholly  produced  by  solution.  That  openings  may 
be  somewhat  prolonged  and  different  openings  connected  by 
solution,  thus  helping  underground  circulation,  is  more  than 
probable,  but  that  important  passages  are  produced  wholly  by 
solution  is  an  assumption  which  I  think  has  not  been  verified 
by  the  facts  of  observation. 

Size  and  Number  of  Openings. — Large  openings  are  favorable 
to  rapid  flowage.  Small  openings  are  unfavorable  to  rapid 
flowage.  This  results  from  the  fact  that  the  friction  between 
the  walls  and  the  moving  column  steadily  becomes  greater  for 
a  given  volume  of  water  as  the  openings  become  smaller. 
Large  openings  are  favorable  to  a  somewhat  direct  course. 
Small  openings  are  favorable  to  a  circuitous  route.  The  direct 
course  of  water  in  large  openings  is  illustrated  by  limestone 
regions,  where  there  are  numerous  large  joints  and  caves  within 
which  the  water  is  quickly  concentrated.  This  being  the  case, 
the  flowage  of  water  is  very  largely  in  the  upper  part  of  the 
zone  of  fracture.  Where  the  openings  are  small,  a  circuitous 
route  must  be  taken,  for  to  pass  a  given  volume  of  water  from 
one  point  to  another  it  is  necessary  that  a  wide  range  of  open- 
ings must  be  used.  This  is  more  fully  explained,  pp.  309-317. 

Fault,  joint,  bedding,  and  fissility  openings  may  be  so  nu- 
merous that  the  pore-space  is  very  large.  Upon  the  average 
fault  openings  are  farther  apart,  but  larger  than  the  joint  open- 
ings, and  joint  openings  are  wider  spaced  and  larger  than  the 
openings  of  fissility.  It  cannot  be  said  which  kind  of  openings 
upon  the  average  gives  the  larger  pore-space.  Since,  however, 
large  openings  are  favorable  to  rapid  flowage,  for  a  given  pore- 
space  the  fault  openings  are  likely  to  give  a  greater  flowage 
than  joint  openings,  and  joint  openings  a  greater  flowage  than 
those  of  fissility.  This  follows  from  the  greater  size  of  the 
fewer  openings.  To  this  is  to  be  added  the  element  of  greater 

*  "The  Genesis  of  Ore-Deposits,"  by  F.  Posepny,  this  volume,  pp.  12-17. 


296      SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

continuity  of  the  larger  openings.  Therefore,  with  a  given 
pore-space,  the  flowage  may  be  vastly  greater  in  the  case  of 
faults  than  in  the  case  of  joints,  and  much  greater  in  the  case  of 
joints  than  in  the  case  of  fissility.  It  will  later  be  explained 
that  the  larger  openings  are  occupied  by  the  trunk  streams,  and 
that  in  these  openings  ores  are  most  likely  to  be  concentrated ; 
hence,  ore-deposits  most  frequently  form  in  fault-fissures,  less 
frequently  in  joints,  and  still  less  frequently  in  the  smaller  and 
more  discontinuous  openings. 

If  the  principle  that  large  openings  are  favorable  to  rapid 
flowage  be  applied  to  mechanical  sediments,  it  follows  that  with 
a  given  pore-space  the  coarse  conglomerates  furnish  a  much 
larger  flow  than  fine  conglomerates,  the  fine  conglomerates  a 
larger  flow  than  the  sandstones,  and  these  a  vastly  larger  flow 
than  the  fine-grained  shales. 

Upon  the  basis  of  size,  openings  in  rocks  may  be  divided  into 
(a)  openings  which  are  larger  than  those  of  capillary  size,  or 
super  capillary  openings,  (b)  capillary  openings,  and  (c)  sub- 
capillary  openings. 

For  water,  openings  larger  than  capillary  openings,  accord- 
ing to  Daniell,*  may  be  circular  tubes  which  exceed  .508  mm. 
in  diameter,  or  may  be  sheet-openings,  such  as  those  furnished 
by  faults,  joints,  etc.,  whose  widths  are  one-half  of  this  or 
exceed  .254  mm.  To  movement  of  water  in  such  openings 
the  ordinary  laws  of  hydrostatics  apply.  Capillary  openings 
for  water  solutions  include  those  which,  if  circular  tubes,  are 
smaller  than  .508  mm.  in  diameter,  or,  if  sheet  spaces,  are  nar- 
rower than  .254  mm.,  and  which  in  either  case  are  larger  than 
the  openings  in  which  the  molecular  attractions  of  the  solid 
material  extend  across  the  space.  Such  openings  in  the  case 
of  circular  tubes  are  those  smaller  than  .0002  mm.  in  diameter, 
or,  if  sheet  passages,  are  below  .0001  mm.  in  width.  Capillary 
openings  therefore  include  circular  tubes  from  .508  mm.  in  di- 
ameter to  .0002  mm.  in  diameter,  and  sheet  passages  from  .254 
mm.  in  width  to  those  .0001  mm.  in  width.  Capillary  openings 
of  other  forms  have  a  range  limited  between  .508  mm.  and 
.0001  mm.,  but  no  one  form  has  so  wide  a  range  as  this.  To 
movement  of  water  in  openings  such  as  these  the  laws  of  cap- 

*  Text-Book  of  Physics,  by  Alfred  Daniell,  3d  ed.,  1894,  pp.  277,  816. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.      297 

illary  flow  apply.  By  subcapillary  openings  are  meant  those  in 
which  the  attraction  of  the  solid  molecules  extends  from  wall 
to  wall.  These  include  all  tubes  smaller  than  .0002  mm.  in  di- 
ameter, and  sheet  openings  smaller  than  .0001  mm.  in  width. 
For  intermediate  forms  the  subcapillary  openings  have  as  their 
maximum  limit  a  range  from  .0002  mm.  to  .0001  mm. 

Within  this  paper  I  cannot  fully  discuss  the  laws  of  flowage 
for  each  of  these  classes  of  openings  and  their  application. 
This  is  fully  done  in  a  treatise  on  "  Metamorphism,"  from 
which  this  paper  is  abstracted.  It  is,  however,  necessary  to 
summarize  the  laws  of  flowage  of  water  in  each  of  the  three 
classes  of  openings. 

The  flowage  of  water  through  supercapillary  tubes  nearly 
follows  the  ordinary  laws  of  hydrostatics,  i.e.9  the  flowage  of 
water  is  as  the  square  root  of  the  pressure  due  to  head.  If 
Y  —  velocity,  H  =  pressure  due  to  head,  and  G  =  force  of 
gravity,  then  V  =  1/2GH.  -For  instance,  the  velocity  result- 
ing from  a  head  of  10  cm.  would  be  the  square  root  of 
2  x  981  x  10  cm. 

This  formula  is  only  approximately  correct,  for  the  internal 
friction  in  supercapillary  tubes  is  dependent  upon  the  viscosity 
of  the  solutions  (a  factor  considered  on  p.  311),  upon  the  regu- 
larity of  the  tubes,  and  upon  the  velocity  of  flowage.  If  the 
tubes  are  not  straight,  eddies  will  form  which  will  increase 
the  internal  friction  and  decrease  the  speed  of  movement.  In 
the  long,  rough,  irregular  underground  passages  not  of  deter- 
minable  size,  eddies  may  so  increase  the  internal  friction  as  to 
render  the  formula  of  hydrostatic  flow  inapplicable.  Further, 
as  a  result  of  the  viscosity,  the  resistance  increases  with  increase 
of  velocity,  so  that  where  the  velocity  of  movement  is  consider- 
able, even  if  the  tubes  are  open  and  continuous,  the  formula 
gives  too  high  results. 

The  flowage  of  water  with  a  given  head  in  supercapillary 
openings  is  very  rapid  indeed,  as  compared  with  the  smaller 
openings.  The  supercapillary  openings  include  the  greater 
number  of  the  fault  openings,  joint  openings,  bedding  partings, 
many  openings  of  fissility,  and  the  openings  in  the  -coarser 
mechanical  sediments,  such  as  very  coarse  sandstones,  and 
conglomerates. 

According  to  Poiseuille's  law,  the  flowage  of  water  in  capil- 


298      SOME   PRINCIPLES    CONTROLLING    DEPOSITION   OF    ORES. 

lary  openings  is  proportional  not  to  the  square,  as  in  supercap- 
illary  openings,  but  to  the  fourth  power  of  the  radius ;  is  pro- 
portional not  to  the  square  root  of  the  pressure,  as  in  supercap- 
illary  openings,  but  to  the  pressure ;  is  inversely  proportional 
to  the  length  of  the  tube ;  and  is  indirectly  proportional  to  the 
viscosity  of  the  liquid.* 

From  the  foregoing  it  follows  that  the  flow  in  a  tube  with  a 
radius  of  .2  mm.  in  diameter  would  be  sixteen  times  as  great 
as  in  a  tube  .1  mm.  in  diameter.  Furthermore,  in  a  tube  of 
a  definite  length,  if  the  pressure  be  doubled  the  flow  would  be 
doubled,  if  trebled  the  flow  be  trebled.  With  a  given  pressure, 
if  the  length  be  doubled  the  flow  would  be  diminished  to  one- 
half,  if  trebled  to  one-third.  The  viscosity  of  underground 
waters  decreases  rapidly  with  the  temperature,  being  only  one- 
fifth  as  much  at  90°  C.  as  at  0°  C.  Therefore,  with  capillary 
tubes  of  a  given  size  the  flowage  would  be  five  times  as  fast  at 
90°  C.  as  at  0°  C. 

How  important  the  laws  of  capillary  flow  are  in  the  move- 
ment of  underground  water  and  the  production  of  ore-deposits 
will  be  understood  when  it  is  known  that  the  openings  of  all 
ordinary  sandstones  and  mechanical  sediments  are  capillary 
openings.  Furthermore,  it  is  to  be  remembered  that  at  a 
depth  of  2700  meters,  supposing  the  increment  to  be  1°  C.  for 
30  meters,  the  temperature  is  90°  C.  Therefore  this  fact, 
because  of  decreased  viscosity,  is  very  favorable  to  the  flowage 
through  the  openings  at  considerable  depth. 

Notwithstanding  the  increased  mobility  of  water,  the  circu- 
lation in  small  capillary  tubes  is  very  slow  indeed ;  so  slow 
that  layers  of  rocks  in  which  the  openings  are  of  small  capil- 
lary size,  such  as  those  of  dense  clays  and  shales,  are  spoken 
of  as  impervious.  Although  this  is  not  exactly  true,  the  move- 
ments of  water  through  such  materials  is  slow  as  compared  with 
the  movement  in  larger  capillary  openings. 

Openings  of  the  third  class  are  subcapillary.     In  these  the 

*  According  to  Poiseuille,  the  general  formula  for  the  flow  through  a  tube  of 

circular  section  is  f  =  -5_P     in  which  /is  the  discharge  in  cubic  centimeters  per 

8/*l 

second,  a  is  the  radius  of  the  tube,  I  its  length,  p  is  the  difference  in  pressure  at 
its  ends  in  dynes  per  square  centimeter,  and  n  is  the  coefficient  of  viscosity  of  the 
liquid.  (See  "Theoretical  Investigation  of  the  .Motion  of  Ground  Waters,"  by 
C.  S.  Slichter,  19^  Ann.  Eep.  U.  S.  Geol  Surv.,  pt.  ii.,  p.  317.) 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       299 

attraction  of  the  solid  molecules  extends  from  wall  to  wall. 
The  water  is  held  as  a  film  glued  to  the  walls  by  the  adhesion 
between  the  water  and  rock.  There  is  no  free  water.  In  such 
openings  as  these  the  flowage  must  be  exceedingly  slow 
or  nil.  Subcapillary  openings  as  here  used  include  also  inter- 
molecular  spaces. 

It  is  evident,  from  the  reasoning  given  on  the  preceding 
pages,  that  the  openings  in  the  zone  of  rock-flowage  are  those 
of  subcapillary  size.  Furthermore,  it  is  evident  that  the  sub- 
capillary  openings  are  discontinuous.  It  has  been  seen  that  at 
a  depth  greater  than  about  11,000  meters  the  water  probably 
has  a  temperature  greater  than  the  critical  temperature  of  water ; 
but  in  the  opinion  of  some  physicists  the  liquid  state  may  per- 
sist even  after  the  critical  temperature  be  passed.*  Whether 
the  H20  below  this  depth  is  a  liquid  or  is  water-gas  cannot  cer- 
tainly be  determined ;  but  it  may  be  supposed  that  the  viscosity 
is  comparatively  small.  Furthermore,  the  water  is  under  enor- 
mous pressures.  Under  circumstances  of  temperature  exceed- 
ing the  critical  temperature  of  water  and  very  great  pressure, 
one  would  be  rash  to  assert  that  water  does  not  pass  through 
the  exceedingly  small  subcapillary  spaces  of  rocks  in  the  zone 
of  flowage,  or  possibly  also  through  the  intermolecular  spaces. 
Some  movement  of  water  might  also  occur  in  connection  with 
the  processes  of  solution  and  deposition,  or  recrystallization, 
which,  as  I  have  explained,  is  characteristic  of  this  zone.  That 
is  to  say,  the  mobility  within  the  solid  material  implies  at  least 
an  equal  mobility  in  the  liquid  material  which  is  also  present. 

In  reaching  a  probable  conclusion  it  is,  however,  to  be 
remembered  that  it  must  be  assumed  that  the  rocks  of  the 
lower  part  of  the  lithosphere  are  also  probably  saturated  with 
water,  and  that  the  pressure  above  is  resisted  by  equal  pressure 
from  below.  Doubtless,  under  the  changing  conditions  caused 
by  rock  deformation,  metamorphism  and  denudation,  and  by 
other  vicissitudes  to  which  the  lower  part  of  the  lithosphere  is 
subjected,  the  water-pressures  become  unequal  at  various  times 
and  places,  and  at  such  times  and  places  there  would  be  an 
undoubted  tendency  for  water  to  move  from  places  of  great 
pressure  to  places  of  less  pressure. 

*  Preston,  "  Theory  of  Heat,"  p.  378. 


300       SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

Whatever  conclusion  may  be  reached  as  to  the  possibility  of 
the  circulation  of  water  in  the  zone  of  rock-flowage,  it  will 
probably  be  agreed  by  all  that  the  circulation,  if  it  occurs  at 
all,  must  be  exceedingly  slow.  Indeed,  upon  this  point  we  are 
not  confined  to  deduction.  We  have  an  almost  certain  infer- 
ence from  the  character  of  the  alterations  which  occur  in  the 
zone  of  rock-flowage.  In  my  treatise  on  Metamorphism  I 
show  that  within  the  zone  of  fracture,  immigration  and  emi- 
gration of  rock-material  is  very  great,  and  that  the  composition 
of  a  rock  may  within  this  zone  be  materially  modified  as  a  con- 
sequence. However,  while  a  rock  in  the  zone  of  flowage  may 
be  transformed  from  a  massive  form  to  a  schist  or  a  gneiss,  the 
composition  of  the  resultant  schist  or  gneiss  is  almost  identical 
with  that  of  the  original  rock.  Had  there  been  rapid  and 
extensive  circulation  of  water  within  this  belt,  it  would  have 
been  inevitable  that  the  composition  of  the  resultant  metamor- 
phosed rocks  would  have  been  different. 

Ore-Deposits  Derived  from  Zone  of  Fracture. 

We  conclude  from  the  foregoing  that  while  underground 
circulation  of  water  upward,  downward,  and  lateral,  is  a  possi- 
bility within  the  zone  of  rock-flowage,  it  is  very  slow,  and  that 
it  cannot  be  appealed  to  to  explain  metalliferous  deposits.  If 
any  one  asserts  that  the  metalliferous  materials  of  mineral  veins 
are  derived  by  water  circulation  from  the  centrosphere,*  or  are 
derived  from  the  lithosphere*  below  the  zone  of  rock-fracture, 
I  hold  this  to  be  a  pure  unverified  assumption  for  which  there 
has  not  as  yet  been  adduced  one  particle  of  evidence,  and  op- 
posed to  which  stand  well-known  principles  of  physics  con- 
cerning the  movement  of  water  in  minute  openings,  and  all 
observations  which  have  been  made  as  to  the  actual  changes 
which  have  taken  place  in  the  rocks  once  within  the  zone  of 
rock-flowage. 

The  original  source  of  much  of  the  material  for  the  metal- 
liferous deposits  may,  indeed,  be  largely  the  centrosphere  or  the 
lower  part  of  the  lithosphere ;  for  from  these  sources  vast  masses 

*  The  term  lithosphere  is  here  applied  to  the  outer  shell  of  earth,  which  is 
known  to  be  solid.  The  term  centrosphere,  following  Powell,  is  applied  to  the 
central  mass  within  the  lithosphere  comprising  the  greater  part  of  the  world,  as 
to  the  character  of  which  we  have  no  definite  knowledge. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       301 

of  volcanic  rock  are  injected  into  the  zone  of  fracture  or  brought 
to  the  surface.  This  is  especially  true  during  great  periods  of 
vulcanism.  Furthermore,  it  is  well  known  that  in  regions  of 
volcanic  rocks  many  ore-deposits  are  found.  Also  it  is  believed 
that  all  the  rocks  of  the  lithosphere  wece.  originally  igneous, 
and  that  from  these  igneous  rocks  the  sedimentary  rocks  have 
been  derived  by  the  epigene  forces,  i.e.,  the  forces  working 
through  the  agencies  of  atmosphere  and  hydrosphere.  It  fol- 
lows, therefore,  that  the  metals  of  ore-deposits,  either  directly 
or  indirectly,  are  derived  from  igneous  rocks.  However,  the 
ores  are  directly  derived  from  rocks  in  the  zone  of  fracture  by 
circulating  underground  waters.  The  rocks  which  furnish  the 
metallic  compounds  may  be  intruded  igneous  rocks ;  they  may 
be  extruded  igneous  rocks ;  they  may  be  the  original  rocks  of 
the  earth's  crust ;  they  may  be  sedimentary  rocks  derived  by 
any  of  the  processes  of  erosion  from  primary  rocks ;  they  may 
be  the  altered  equivalents  of  any  of  these  classes. 

That  there  is  a  sufficient  amount  of  metalliferous  material 
within  the  rocks  of  the  zone  of  fracture  to  account  for  all 
metallic  deposits  will  be  admitted  by  all.  It  is  well  known 
that  the  amount  of  material  which  it  is  necessary  to  suppose 
to  be  originally  present  in  the  country-rock  within  the  reach 
of  the  underground  water  circulation  in  the  zone  of  fracture, 
in  order  to  fully  account  for  the  ore-deposits,  is  an  exceedingly 
small  fraction  of  1  per  cent. ;  such  small  fractions  in  the  case 
of  the  rarer  metals  that  the  numbers  have  little  significance  to 
us.  Even  in  the  case  of  the  common  metals,  such  as  iron,  lead, 
zinc  and  copper,  the  fraction  of  a  per  cent,  which  it  is  necessary 
to  suppose  to  be  present  is  exceedingly  small.  This  is  well 
illustrated  by  the  lead-  and  zinc-district  of  southwestern  Wis- 
consin. Here,  according  to  Prof.  Chamberlin,  Mr.  Buell  has 
calculated  that  if  the  source  of  the  metal  in  the  Potosi  district, 
the  richest  in  the  region,  be  restricted  to  a  layer  100  feet  deep 
and  limited  on  the  outside  of  the  area  of  paying  crevices  by 
half  the  average  distance  between  the  crevices,  to  account  for 
all  the  lead  which  had  been  taken  out,  it  would  only  be  neces- 
sary to  suppose  that  the  rock  contained  "  one-fourteen-hun- 
dredth of  one  per  cent.,  or  a  little  more  than  seven  millionths 
part  of  the  rock."* 

*  "  Ore-Deposits  in  Southwestern  Wisconsin,"  by  T.  C.  Chamberlin,  Geol.  oj 
Wis.t  vol.  iv.,  1882,  pt.  iv.,  p.  538. 


302       SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

The  second  fundamental  premise  of  this  paper  is,  that  the  material 
for  ore-deposits  is  derived  from  rocks  within  the  zone  of  fracture. 

The  Source  of  Underground  Water. 

Since  it  has  been  shown  it  cannot  be  assumed  that  there  is 
any  considerable  circulation  of  underground  water  in  the  zone 
of  rock-flowage,  it  follows  that  we  cannot  suppose  that  the 
water  of  the  zone  of  fracture  passes  into  or  is  derived  from  the 
zone  of  rock-flowage  on  any  large  scale.  Doubtless  this  trans- 
fer does  take  place  to  some  small  extent.  Also,  through  the 
agency  of  vulcanism  water  occluded  in  magma  is  transferred 
from  the  zone  of  rock-flowage,  or  even  possibly  from  the  cen- 
trosphere,  to  the  zone  of  rock-fracture.  Furthermore,  hydration 
and  dehydration  of  the  rocks  are  constantly  taking  place,  and 
these  processes  may  not  balance.  However,  the  amount  of 
underground  water  coming  from  the  deep-seated  zone  of  rock- 
flowage  in  these  ways  at  any  one  time  is  relatively  small,  and 
therefore  the  meteoric  water  entering  the  crust  substantially 
balances  that  issuing  from  it.  Hence,  so  far  as  the  main  work 
of  ore-deposition  is  concerned,  the  water  is  that  of  the  zone  of 
rock-fracture,  and  this  water  is  water  of  meteoric  origin,  which 
makes  its  way  from  the  surface  into  the  ground,  and  there 
performs  its  work  and  issues  to  the  surface  again. 

The  third  premise  of  this  paper  is  that  by  far  the  major  part  of 
the  water  depositing  ores  is  meteoric. 

The  Cause  of  the  Flowage  of  Underground  Water. 

The  fourth  premise  of  this  paper  is,  that  the  flowage  of  under- 
ground water  is  caused  chiefly  by  gravitative  stress. 

Gravity  is  effective  in  the  movement  of  underground  water 
in  proportion  to  the  head.  Head  is  due  to  the  fact  that  the 
water  entering  the  ground  at  a  certain  level,  after  a  short  or 
long  underground  journey,  issues  at  a  lower  level. 

The  efficiency  of  gravity  is  also  dependent  upon  temperature. 
In  so  far  as  water  is  warmer  at  its  point  of  issuance  than  it  was 
when  it  joined  the  sea  of  underground  water,  this  is  favorable 
to  circulation,  and  gives  an  effect  in  the  same  direction  as  head. 
This  is  due  to  the  fact  that  the  density  of  water  varies  inversely 
with  the  temperature. 

Taking  the  volume  of  water  at  4°  XX  as  1,  its  volume  at  50° 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       303 

C.  would  be  1.0120;  at  75°  C.  would  be  1.0258,  and  at  100° 
C.  would  be  1.0432.*  Therefore  the  increase  in  the  tempera- 
ture of  underground  water  may  lessen  its  density  as  much  as  4 
per  cent,  without  exceeding  its  boiling-point  at  normal  pressure, 
and  a  diminution  of  density  of  1  per  cent,  or  more  is  probably 
not  uncommon.  It  is  therefore  evident  that  in  columns  of 
water  of  equal  length  the  stress  of  gravity  is  considerably 
greater  upon  the  column  having  the  lower  temperature.  That 
the  difference  in  gravitative  stress,  due  to  difference  in  tem- 
perature, may  be  sufficient  to  produce  rapid  circulation  in 
pipes  which  are  supercapillary,  is  shown  by  the  use  of  the 
principle  in  the  hot-water  system  of  heating  buildings.  Under- 
ground, as  in  the  hot-water  system  of  heating,  heat  is  the 
energy  which  causes  the  water  to  expand,  and  gives  a  differ- 
ence in  density.  When  heat  has  produced  a  difference  in 
density  of  the  two  columns,  gravity  is  the  force  which  inaugu- 
rates and  maintains  the  circulation. 

It  is  believed  that  underground  circulation  may  be  promoted 
in  an  important  degree  by  difference  in  temperature  of  the 
descending  and  ascending  columns  of  water,  resulting  from 
heat  abstracted  from  the  rocks,  due  wholly  to  their  normal 
increment  of  temperature  with  depth.  Later  it  will  be  shown 
that  the  downward  moving  water  is  ordinarily  dispersed  in 
many  small  openings  and  moves  relatively  slowly.  Therefore  it 
may  be  supposed  at  any  given  place  to  have  approximately  the 
temperature  of  the  rocks.  The  upward  movement  of  water, 
upon  the  contrary,  is  shown  to  be  usually  in  the  larger  open- 
ings and  relatively  rapid.  Therefore  at  any  given  place  its 
temperature  is  probably  higher  than  is  normal  for  the  rocks  at 
that  depth.  The  result  is  to  give  the  descending  and  ascend- 
ing columns  a  difference  in  temperature,  the  ascending  column 
being  hotter.  As  already  noted,  the  expansion  of  water  with 
increase  of  temperature  is  considerable,  amounting  to  over  4 
per  cent,  between  0°  C.  and  100°  C.,  that  is,  a  given  mass  of 
water  would  occupy  a  volume  4  per  cent,  greater.  In  other 
words,  if  there  is  an  average  difference  of  100°  C.  in  the  ascend- 
ing and  descending  columns,  100  feet  of  the  downward  moving 

*  "  Exercises  in  Physical  Measurements,"  by  L.  W.  Austin  and  C.  B.  Thwing 
1896,  p.  151. 


304       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

water  would  balance  104  feet  of  the  upward  moving  water.  If 
we  suppose  the  descending  and  ascending  columns  to  be  con- 
nected, of  equal  height,  and  having  an  average  difference  of 
100°  C.  in  temperature,  this  would  be  equivalent  to  a  head  of 
4  feet  per  100  feet  all  along  the  length  of  the  column.  Prob- 
ably the  difference  in  temperature  between  the  columns  is  not 
often  so  great  as  100°  C.,  but  the  illustration  shows  that  the 
difference  in  temperature  between  ascending  and  descending 
columns  of  the  same  length  may  give  a  sufficient  stress  to  over- 
come friction  and  viscosity,  and  give  a  somewhat  rapid  move- 
ment to  underground  water. 

As  an  illustration  of  the  principle  may  be  mentioned  the 
water-power  of  the  sea-mills  of  Cephalonia,  which,  according 
to  the  Crosbys,  is  wholly  due  to  the  difference  in  the  tempera- 
ture of  the  descending  and  ascending  waters.*  In  regions 
where  vulcanism  or  dynamic  action  has  recently  occurred,  the 
difference  in  density  resulting  from  difference  in  temperature 
in  the  descending  and  ascending  columns  may  be  an  even 
more  important  influence  in  the  circulation  of  the  underground 
waters  than  in  regions  where  the  high  temperature  is  due  to 
the  normal  heat  of  the  rocks.  Such  a  region  is  the  Yellow- 
stone Park. 

In  some  cases  the  issuing  water  throughout  a  great  region 
is  very  clearly  at  a  higher  temperature  than  the  entering  water, 
and  in  such  regions  this  difference  in  temperature  must  be  a 
very  important  factor  in  its  underground  circulation.  In  such 
cases  the  difference  in  temperature  of  the  descending  and  as- 
cending waters  generally  results  from  the  normal  increase  of 
temperature  due  to  depth,  from  regional  vulcanism,  and  from 
the  rocks  having  a  higher  temperature  than  normal  because 
of  recent  orogenic  movements. 

An  excellent  illustration  of  such  a  region  is  the  Cordilleran 
region  of  the  western  United  States,  in  which  there  are  many 
valuable  ore-deposits.  Gilbertf  and  others  have  shown  that 
scattered  throughout  this  vast  region,  occupying  nearly  one- 

*  "The  Sea-Mills  of  Cephalonia,"  by  W.  F.  Crosby  and  W.  O.  Crosby,  Tech. 
Quar.,  vol.  ix.,  1896,  pp.  6-23. 

f  "The  Geology  of  Portions  of  Nevada,  Utah,  California  and  Arizona,  Ex- 
amined in  the  years  1871  and  1872,"  by  G.  K*  Gilbert,  Rept.  Geog.  and  Geol. 
Surveys  west  of  100th  Meridian,  vol.  iii.,  1873,  pt.  1,  pp.  148-149. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       305 

third  of  the  United  States,  are  many  hot  springs,  the  tempera- 
tures of  which  vary  from  37°  C.  to  100°  C.  More  numerous 
than  these  are  the  warm  springs,  the  temperatures  of  which  are 
below  blood  heat.  The  warm  springs  may  be  considered  as 
including  those  between  18°  C.  and  37°  C.  According  to 
Gilbert,  the  water  of  all  the  foregoing  springs  exceeds  the  mean 
annual  temperature  of  the  region  by  8.3°  C. 

Although  we  have  no  data  by  which  to  verify  the  statement, 
E  have  no  doubt  whatever  that  the  springs,  the  temperature  of 
which  is  above  the  mean  annual  temperature,  but  less  than 
8.3°  C.  above,  exceed  by  many  times  the  total  of  all  springs 
the  temperatures  of  which  are  8.3°  C.  or  more  above  the  normal 
temperature  of  the  region.  And  it  is  to  be  remembered  that 
a  slightly  increased  temperature  of  issuing  water  over  that  of 
the  falling  water  through  the  vast  number  of  springs  and 
through  seepage  is  of  far  greater  quantitative  importance  than 
the  marked  increase  of  temperature  in  the  comparatively  few 
warm  and  hot  springs.  This  illustrates  the  old  principle 
that  the  widespread,  moderate  forces  are  incomparably  more 
important  than  the  more  conspicuous,  but  more  circumscribed 
forces. 

While  gravity  is  the  only  important  force  to  which  appeal  can 
be  made  to  account  for  the  circulation  of  waters  producing  ore- 
deposits,  circulation  in  some  small  degree  does  result  from 
other  immediate  causes.  For  instance,  earth  movements  may 
deform  the  rocks,  and  in  this  process  squeeze  out  the  water, 
as  in  the  production  of  the  crystalline  schists  from  the  sedi- 
mentary rocks.  If  the  deformation  of  the  rocks  be  referred 
to  their  ultimate  cause,  gravity,  even  the  circulation  of  the 
water  resulting  from  deformation  is  indirectly  due  to  the  stress 
of  gravity.  However,  the  important  immediate  causes  of  move- 
ments of  underground  water  below  water  level  are  two — gravity 
and  deformation. 

But  whatever  the  cause  of  the  flow  of  underground  water, 
the  direction  of  movement  is  from  places  of  greater  pressure 
to  places  of  less  pressure.  A  current  going  in  any  direction 
is  evidence  of  an  excess  of  pressure  in  the  rear  of  the  current. 
Thus,  water  which  enters  by  seepage  or  through  capillary  tubes 
into  a  larger  opening,  such  as  a  fissure,  must  be  under  greater 
pressure  than  the  column  of  water  into  which  it  makes  its 


306      SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OP    ORES. 

way.  Whether  the  motive  force  in  the  movement  of  the 
water  is  difference  in  gravitative  stress  or  deformation,  or  any 
other  cause,  the  excess  of  pressure  resulting  in  movement  is 
behind  the  current. 

In  the  foregoing  statement  as  to  the  cause  of  the  movement 
of  underground  water,  only  the  vertical  component  of  the 
columns  has  been  considered.  The  horizontal  component  of 
the  column  has  no  effect.  So  far  as  there  is  horizontal  move- 
ment, the  energy  required  for  this  movement  to  overcome  fric- 
tion and  internal  viscosity  is  derived  from  the  forces  already 
mentioned, — that  is,  gravitative  stress  or  deformation. 

Sells  of  Underground  Circulation. 

The  circulation  of  underground  water  is  divided  into  two 
parts :  that  of  an  upper  belt  above  the  level  of  groundwater, 
and  a  lower  belt  below  the  level  of  groundwater. 

Upper  Bell  of  Underground  Circulation. — The  upper  belt  of 
underground  water  circulation  extends  from  the  surface  to  the 
level  of  groundwater.  The  thickness  of  this  outer  belt  of 
water  circulation  varies  greatly.  At  or  near  streams,  lakes,  or 
ocean,  and  in  areas  where  the  surface  is  not  much  higher  than 
the  adjacent  bodies  of  water,  the  level  of  groundwater  may 
reach  near  or  to  the  surface,  and  thus  there  may  be,  for  these 
areas,  either  a  very  thin  upper  belt  of  circulation,  or  none.  In 
regions  of  moderate  elevation  and  moderate  irregularities  of 
topography  the  level  of  groundwater  is  usually  from  10  feet 
to  100  feet  below  the  surface.  It  is  especially  likely  to  be  near 
the  surface  in  regions  where  there  is  a  thick  layer  of  drift  or  a 
thick  layer  of  disintegrated  rocks.  In  elevated  and  irregular 
regions,  and  especially  those  in  which  the  precipitation  is  rather 
small,  the  level  of  groundwater  may  be  from  100  to  300  feet 
below  the  surface.  In  high,  desert  regions,  and  especially 
limestone  regions,  the  level  of  groundwater  may  be  from  a 
thousand  to  several  thousand  feet  below  the  surface. 

The  position  of  the  level  of  groundwater  is  more  fully  con- 
sidered further  on,  in  connection  with  the  belt  below  that  level. 

A  large  amount  of  the  water  which  enters  the  upper  belt  is, 
without  entering  the  lower  belt,  again  brought  to  the  surface 
through  capillarity,  or  through  the  influence  of  vegetation. 
The  circulation  of  this  water  in  the  upper  belt  alone  has  little 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       307 

influence  upon  the  ore-deposits,  and  is  here  ignored.  Another 
portion  of  the  ground  water  moves  downward  through  the  upper 
belt  and  joins  the  sea  of  underground  water.  This  water  is 
associated  with  oxygen,  carbon-dioxide,  and  other  gases.  These 
substances  perform  various  classes  of  work,  which  are  consid- 
ered on  pp.  329-334. 

Lower  Belt  of  Underground  Circulation. — The  lower  belt  of 
circulation  has  as  its  upper  limit  the  level  of  groundwater. 
This  level  is  not  horizontal,  but  is  undulating,  the  undulations 
following  the  topography.  A  topographic  map  of  a  region  is 
to  a  certain  extent  a  topographic  map  of  the  level  of  ground- 
water  ;  but  the  latter  is  less  accentuated.  The  elevation  of  the 
contour  of  the  groundwater  at  a  given  place  is  less  than  the 
elevation  of  the  surface  contour  by  the  depth  of  the  level  of 
groundwater. 

That  the  level  of  groundwater  roughly  follows  the  topography 
is  shown  by  the  fact  that  upon  many  hills  and  mountains,  wells 
reach  water  at  the  very  moderate  depths  of  a  few  score,  or  at 
most-100  or  200  feet.  The  relation  is  further  illustrated  by  the 
fact  that  where  a  shore  begins  to  rise  from  a  body  of  water,  as 
from  a  lake,  the  level  of  groundwater  also  rises,  but  not  so  rap- 
idly. As  an  example  of  this  may  be  mentioned  the  case  of  a 
well  at  Madison,  Wisconsin,  about  1200  feet  from  Lake  Men- 
dota  and  88  feet  above  its  surface,  in  which  the  water  is  on  an 
average  about  52  feet  above  the  surface  of  the  lake.* 

In  general,  the  more  accentuated  the  topographic  features, 
the  greater  is  the  difference  between  the  surface  topography 
and  that  of  the  level  of  groundwater.  However,  this  difference 
also  depends  upon  the  character  of  the  rocks.  Where  the 
openings  in  the  rocks  are  numerous  and  large,  there  is  a  greater 
difference  in  the  topography  of  the  surface  and  of  the  level  of  the 
groundwater  than  where  the  rocks  are  less  open.  In  fractured 
limestone  regions  containing  caves,  the  level  of  the  ground- 
water  may  follow  approximately  that  of  the  drainage  of  the 
district,  and  thus  there  be  a  great  difference  between  the  topog- 
raphy of  the  surface  and  that  of  the  groundwater.  "Where  a 
region  is  covered  with  a  thick  mantle  of  fine  material,  as  drift, 


*  "  Principles  and  Conditions  of  Movements  of  Groundwater,"  by  F.  H.  King, 
19th  Annual  Rept.  U.  S.  Geol  Surv.,  for  1897-98,  pt.  ii.,  p.  99,  1899. 

20 


308       SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

the  topography  of  the  groundwater  may  very  closely  follow 
that  of  the  surface.  Finally,  the  less  the  precipitation  the 
greater  the  difference  between  the  contours  of  the  surface  and 
the  level  of  groundwater.  In  the  Grand  Canon  region  of 
Colorado  we  have  a  district  in  which  the  topography  is  much 
accentuated  with  sudden  and  great  changes  in  elevation,  in 
which  the  rocks  are  largely  limestone  and  the  precipitation 
small.  Therefore  in  this  region  there  is  a  very  great  difference 
between  the  topography  of  the  surface  and  that  of  the  level  of 
groundwater. 

Capacity  of  Water  for  Work  in  the  Lower  Belt  of  Under- 
ground Circulation.  —  The  temperature  of  water  in  the  lower 
belt  of  underground  circulation  increases  with  depth.  The 
average  increment  is  about  1°  C.  for  30  meters.  Supposing  the 
water  at  the  surface  to  be  0°  C.,  it  would  be  100°  C.  at  a  depth 
of  3000  meters.  At  a  depth  of  10,000  meters  it  would  be  333°  C. 
It  has  been  shown,  pp.  291-293,  that  the  pressure  increases  with 
depth  with  sufficient  rapidity  to  hold  the  water  in  the  form  of 
a  liquid.  Therefore  the  work  of  the  water  in  the  zone  of  frac- 
ture below  3000  meters  is  that  of  superheated  water.  It  is 
well  known  that  pure  water  at  ordinary  temperatures  is  capable 
of  dissolving  all  compounds  to  some  extent,  but  the  amount  of 
the  more  refractory  compounds  dissolved  is  exceedingly  small. 
But  pure  water  at  a  high  temperature  is  a  potent  solvent. 
Bar  us  has  shown  that  water  at  temperatures  above  185°  C. 
attacks  the  silicates  composing  soft  glass  with  astonishing 
rapidity.* 

At  180°  C.  various  zeolites  can  be  dissolved  in  pure  water, 
the  material  crystallizing  out  on  cooling.  Lemberg  shows  that 
water  at  210°  C.  slowly  dissolved  anhydrous  powdered  silicates. 
It  is  therefore  apparent  that  water  in  the  lower  part  of  the  zone 
of  fracture  is  a  most  potent  chemical  agent. 

Furthermore,  it  is  well  known  that  one  salt  in  solution  may 
assist  water  in  dissolving  another  salt.  For  instance,  the  pres- 
ence of  alkaline  sulphides  is  very  favorable  to  solution  of  sul- 
phides of  the  heavy  metals,  such  as  copper,  silver  and  gold. 
On  the  other  hand,  the  presence  of  one  compound  in  solution 


*  '  '  Hot  Water  and  Soft  Glass  in  their  Thermo-dynamic  Eelations,  by  C.  Barus, 
Am.  Jour.  Sci.,  IV.,  vol.  ix.,  1900,  pp.  161-175.' 


SOME   PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       309 

may  be  unfavorable  to  the  solution  of  another  compound.  Thus 
in  the  underground  waters  the  material  in  solution  continually 
affects  the  capacity  of  the  water  to  dissolve  and  precipitate 
other  materials.  This  subject  will  be  further  discussed,  pp. 
324-326. 

Movements  of  Water  in  the  Lower  Belt  of  Underground  Cir- 
culation. —  The  complex  movements  of  underground  water  may 
be  resolved  into  two  components,  horizontal  or  lateral  movements 
and  vertical  movements. 

The  vertical  component  of  the  journey  of  underground 
waters  in  the  zone  below  the  level  of  groundwater  may  be 
considered  as  confined  to  the  zone  of  fracture,  and  is  probably 
measured  at  a  maximum  by  10,000  meters,  or  at  most  by  12,- 
000  meters.  The  lateral  component,  on  the  other  hand,  may 
vary  from  a  few  meters  to  hundreds  or  even  a  thousand  or 
more  kilometers.  Upon  the  average,  the  horizontal  component 
is  probably  far  greater  than  the  vertical  component. 

In  order  to  understand  the  work  done  by  underground  water 
in  its  journey,  it  is  first  necessary  to  know  the  path  which  it 
follows.  Upon  this  point  the  recent  analytical  work  of  Prof. 
C.  S.  Slichter*  gives  the  desired  information.  He  has  ascer- 
tained that  the  spaces  in  soils  and  in  mechanical  sediments,  so 
far  as  the  flowage  of  underground  water  is  concerned,  may  be 
considered  as  a  series  of  triangular  tubes.  By  Prof.  Slichter's 
analysis  the  flowage  of  water  from  one  place  to  another,  say 
from  A  to  B  (see  Fig.  1),  is  not  by  a  direct  path,  but  by  a  large 
number  of  diverging  paths  from  A  during  the  first  part  of  the 
journey,  and  by  a  large  number  of  converging  paths  to  B  dur- 
ing the  latter  part  of  the  journey.  This  may  be  illustrated  by 
supposing  the  water  to  be  poured  into  a  well,  A,  and  to  flow  to 
a  well,  B.  The  horizontal  course  of  the  water  is  represented 
by  Fig.  1,  and  the  vertical  course  by  Fig.  2.  These  conclu- 
sions apply  equally  well  to  any  porous  rock  other  than  a  soil 
or  sandstone  in  which  the  spaces  are  distributed  in  a  somewhat 
uniform  manner. 

It  is  apparent  that  these  conclusions  have  far-reaching  con- 
sequences as  to  the  flowage  of  underground  water.  In  the 


*  "  Theoretical  Investigation  of  the   Motion  of  Ground  Waters,"   by  C.  S. 
Slichter,  19<A  Ann.  Kept.  U.  S.  Geol.  Surv.,  for  1897-98,  p.  312. 


310      SOME   PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

passage  of  the  water  from  the  top  or  slope  of  a  hill  to  a 
point  of  issue  at  the  foot  of  the  hill,  supposing  these  to  be 
the  only  points  of  entrance  or  issuance  of  the  water,  and 

FIG.  1. 


Ideal  Horizontal  Section  of  the  Flow  of  Underground  Water  through  a  Homo- 
geneous Medium,  from  One  Well  to  Another. 

supposing  the  spaces  to  be  uniform,  the  vertical  course  would 
be  represented  by  the  lines  of  Fig.  3,  and  the  horizonal  course 
would  be  represented  by  the  lines  of  Fig.  1.  We  see  at  once 
that  for  the  larger  topographic  features  the  vertical  component 
of  flow  may  pass  quite  to  the  lower  limit  of  the  zone  of  frac- 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       311 

ture.  This  would  probably  be  true  even  if  water  throughout 
its  underground  journey  remained  at  a  constant  temperature. 
But  it  is  to  be  remembered  that  the  deeper  water  penetrates,  the 
higher  its  temperature ;  also  that  the  movement  of  water  in  the 

FIG.  2. 


Ideal  Vertical  Section  of  the  Flow  of  Underground  Water  through  a  Homogene- 
ous Medium,  from  One  Well  to  Another. 

lower  part  of  the  zone  of  fracture  is  largely  through  capillary 
openings ;  further,  that  the  flowage  in  capillary  openings  is  in- 
versely as  the  viscosity ;  and,  finally,  that  the  viscosity  decreases 
rapidly  with  increase  of  temperature.  Therefore,  the  increase 
of  temperature  with  depth  is  a  potent  factor  favorable  to  a  deep 
course  for  underground  water.  It  therefore  seems  probable 


312      SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

that  as  a  result  of  head  due  to  topographic  irregularities  and 
temperature  differences,  the  entire  zone  of  fracture  is  being 
regularly  traversed  by  underground  waters.  Of  course,  the 

FIG.  3. 

A* 


Ideal  Vertical  Section  of  the  Flow,  through  a  Homogeneous  Medium,  of  Under- 
ground Water  Entering  at  One  Point  on  a  Slope  and  Issuing  at  a  Lower  Point. 

amount  of  flowage  is  far  greater  in  the  upper  part  of  the  zone 
than  in  the  lower  part,  but  even  in  the  lower  half  or  third  of  the 
zone  of  fracture  the  amount  of  flowage  cannot  be  considered 
small. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       313 

The  principle  of  the  distribution  of  the  flowage  of  water 
over  the  entire  available  area  is  well  illustrated  by  the  case  of 
water  flowing  horizontally  into  a  beaker  from  one  side  and 
overflowing  the  beaker  on  the  other  side.  The  movement  of 
the  water  will  not  be  confined  to  the  liquid  near  the  surface  of 
the  beaker,  but  all  portions  of  the  water  in  the  beaker  from 
the  top  to  the  very  bottom  will  take  part  in  the  flowage, 
although,  of  course,  the  rate  of  movement  will  be  much  more 
rapid  at  the  top  than  at  the  bottom.*  The  well-known  hydro- 
dynamical  principle  thus  illustrated,  that  the  entire  available 
cross-section  will  always  be  utilized  by  flowing  currents,  is 
directly  applicable  to  lateral  moving  waters  in  the  zone  of  frac- 
ture. It  is  conclusive  evidence  that  this  zone  will  be  searched 
to  its  base  by  moving  waters,  although  the  waters  joining  and 
departing  from  the  underground  sea  appear  and  disappear  at 
the  surface. 

In  an  actual  case  of  underground  flowage  the  wTater  does  not 
enter  the  ground  at  a  single  point,  but  enters  at  every  point  of 
a  slope.  As  a  sample  case,  we  may  suppose  that  the  water  en- 
tering on  a  slope  reaches  the  surface  again  at  the  level  of  a 
stream  in  an  adjacent  valley.  To  get  an  idea  of  the  complex- 
ity of  the  flow  in  this  ideal  case,  we  may  arbitrarily  select  a 
number  of  points  where  the  water  enters,  and  trace  out  its 
course.  We  may  plat  by  different  kinds  of  lines,  continuous 
and  broken,  the  vertical  components  of  the  flowage  of  the 
water  which  enters  at  each  place  independently  of  the  water 
that  enters  at  other  places.  (Fig.  4.)  We  have  a  series  of 
intersecting  lines  in  the  figure  representing  the  vertical  com- 
ponents of  movement. 

It  is  not  supposed  that  water  actually  follows  paths  similar 
to  those  represented  by  the  figure,  for  there  is  mutual  interfer- 
ence of  the  water  entering  at  the  various  points.  As  a  result 
of  this,  the  water  entering  the  opening  nearest  the  exit  would 
take  a  more  direct  course  than  the  average  of  that  platted ;  but, 
as  a  consequence  of  this,  the  water  from  the  next  openings  up 
the  slope  would  take  a  more  indirect  course,  on  the  average, 
than  that  platted,  and  so  on.  The  total  result  would  be  to  give 

*  Slichter,  cit.,  p.  331,  sect.  5.     Compare  Posepny,  cit.,  this  volume,  p.  26. 


314      SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

an  average  course  for  the  water  which  can  be  represented  by 
combining  the  independent  curves.  (Fig.  5.)  The  effect,  so 
far  as  the  geological  action  of  the  underground  water  is  con- 

FIG.  4. 


Ideal  Vertical  Section  of  the  Flow,  through  a  Homogeneous  Medium,  of  Under- 
ground Water  Entering  at  Three  Points  and  Issuing  at  a  Single  Point,  Each  Sys- 
tem of  Flow  Being  Independent  of  the  Others. 

cerned,  would  be  approximately  the  same,  whether  the  course 
of  the  water  were  that  represented  by  Fig.  4  or  that  repre- 
sented by  Fig.  5.  This  statement,  applicable  to  a  few  points  of 
entrance  and  one  of  exit,  is  equally  applicable  to  a  great  num- 
ber of  points  of  entrance.  The  statement  can  be  further  ex- 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       315 

tended  to  an  indefinite  number  of  points  of  entrance  distributed 
along  the  contours  of  the  slope  as  well  as  up  the  slope,  and  to 
many  points  of  exit  at  or  near  the  level  of  the  valley. 

The  Preferential  Use  by  Water  of  Large  Channels. — In  nature 
the  points  of  entrance  for  groundwater  are  indefinitely  numer- 

FIG.  5. 


Ideal  Vertical  Section  of  the  Flow,  through  a  Homogeneous  Medium,  of  Under- 
ground Water  Entering  at  Many  Points  along  a  Slope  and  Issuing  at  a  Single  Point 
of  Lower  Elevation. 

ous,  and  the  places  of  exit  comparatively  few.  The  water  falls 
upon  the  ground  everywhere  and  enters  the  innumerable  pores 
between  the  grains.  After  a  longer  or  shorter  underground 
course,  perhaps  passing  under  many  subordinate  hills  and  val- 
leys, it  escapes  to  the  surface  as  a  spring  or  by  seepage,  nearer 
the  drainage-level  than  where  it  entered  the  ground.  The 


316       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

water  began  its  journey  through  an  almost  infinite  number  of 
openings.  It  issues  at  many  openings,  but  these  are  few  com- 
pared with  the  vast  number  of  those  at  which  it  entered. 

This  conclusion  is  based  on  the  following  facts :  Openings  in 
rocks  are  never  of  uniform  size.  It  has  been  seen  that  the  resist- 
ance to  flowage  in  capillary  openings  is  far  greater  than  in  super- 
capillary  openings.  In  supercapillary  openings  of  moderate 
size  the  resistance  is  greater  per  unit  of  flowage  than  in  larger 
ones.  Thus  there  is  a  strong  tendency  for  the  water  starting 
through  innumerable  small  openings  to  converge  into  larger 
and  larger  openings,  which  are  the  lines  of  least  resistance. 
Of  course,  it  may  go  long  distances  underground,  as  in  some 
sandstones,  without  finding  larger  openings  than  those  near  the 
surface ;  but  if  large  openings  exist,  they  will  be  fully  utilized. 
Finally,  when  a  single  opening  or  a  group  of  openings  larger 
than  the  average  reach  the  surface  at  a  lower  altitude  than  the 
average  level  of  entrance  of  the  water,  there  is  a  spring. 

It  has  been  seen  that  during  the  first  part  of  the  under- 
ground journey  of  water  the  vertical  component  is  downward, 
and  during  the  latter  part  of  its  journey  the  vertical  compo- 
nent of  much  of  it  is  upward.  It  follows  that,  on  the  average, 
the  downward  movements  of  water  are  through  the  smaller, 
and  the  upward  movements  through  the  larger,  openings  in 
the  rocks.  Of  course,  where  large  openings  are  available  for 
the  downward-moving  water  they  will  be  utilized ;  and  doubt- 
less the  larger  openings  are  utilized  to  a  great  extent  by  the 
downward  moving  waters.  However,  even  if  this  be  the  case, 
the  statement  would  still  be  true  that  upon  the  average  the 
larger  openings  are  more  extensively  used  by  the  upward 
moving  water  than  by  the  downward  moving  water.  From 
the'  foregoing  it  appears  that  the  system  of  circulation  of 
underground  water  has  a  very  close  analogy  to  that  of  a  tree 
of  a  peculiar  character. 

The  points  of  entrance  are  the  ends  of  the  indefinite  number 
of  twigs;  these  twigs  unite  into  a  branch;  the  branches 
unite  to  produce  a  larger  branch ;  the  larger  branches  unite 
into  a  trunk;  and  at  the  end  of  a  trunk  is  a  spring.  The 
analogy  of  an  underground  drainage  system  to  a  tree  is  even 
closer  than  that  of  a  surface  system,  for  in  a  system  of  under- 
ground water  circulation  three  dimensions  are  concerned  to  an 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.      317 

important  extent,  while  in  a  surface  system  of  drainage  the 
movement  of  the  water  is  approximately  confined  to  a  plane. 
However,  from  what  has  gone  before,  it  is  clear  that  the  tree 
of  underground  water  has  a  peculiar  shape.  The  twigs  and 
branches  have  an  important  downward  component;  the  larger 
branches  of  the  tree  may  be  considered  as  approximately  hori- 
zontal ;  and  the  trunk  usually  has  an  important  upward  com- 
ponent. Thus  twigs,  branches  and  trunks  together  ordinarily 
make  a  great  U.  The  sides  of  the  U  may  be  rather  close  together 
in  the  case  of  marked  topography,  where  the  water  issues  near 
the  places  of  entrance.  The  sides  of  the  U  may  be  very  far 
apart  in  the  case  of  gentle  topography,  where  there  is  great 
lateral  movement  of  the  water.  Such  a  system  of  under- 
ground movement  is  somewhat  similar  to  that  of  a  surface 
system  of  drainage. 

The  analogy  of  a  tree  has  been  utilized  in  order  to  get  defi- 
nitely in  mind  the  general  character  of  the  circulation  of 
underground  water.  However,  the  analogy  must  not  be 
pushed  too  far.  A  tree  commonly  has  but  a  single,  continu- 
ous, solid  trunk,  although  willows  and  other  trees  have  many 
trunks.  Very  frequently,  indeed  commonly,  the  trunk-chan- 
nels of  underground  water  circulation  are  very  complex. 
While  a  main  water  course  may  exceptionally  occupy  a  single 
open  passage,  ordinarily  it  is  composed  of  a  number  of  inter- 
locking passages.  These  may  be  the  parallel  openings  of  a 
complex  fault,  they  may  be  the  smaller  numerous  openings  of  a 
zone  of  fissility,  or  they  may  be  the  more  open  spaces  of  sand- 
stones or  conglomerates.  In  short,  a  trunk-channel  of  under- 
ground water  differs  only  from  other  channels  in  that  they  are 
places  where  there  is  more  circulation. 

PHYSICO-CHEMICAL   PRINCIPLES    CONTROLLING    THE   WORK    OF 

UNDERGROUND  WATERS. 

Before  considering  the  actual  geological  work  of  under- 
ground water  in  the  alteration  of  the  rocks  and  in  the  pro- 
duction of  ore-deposits,  it  is  necessary  to  consider  briefly  the 
physico-chemical  principles  which  control  that  work.* 

*  In  my  treatise  on  ' '  Metamorphism  ' '  (Monograph  U.  S.  Geol.  Survey)  I  con- 
sider this  subject  in  detail.  In  the  present  paper,  only  that  portion  of  this  part 
of  the  Monograph  is  summarized  which  is  absolutely  necessary  in  order  to  under- 
stand the  deposition  of  ore-deposits. 


318       SOME   PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

Chemical  Action. 

The  fundamental  principle  of  chemical  dynamics  is  that 
chemical  action  is  proportional  to  the  active  mass.  This  is  the 
law  of  mass  action.* 

Chemical  action  may  take  place  between  gases  and  gases, 
between  gases  and  liquids,  between  gases  and  solids,  between 
different  liquids,  between  liquids  and  solids,  between  different 
solids.  So  far  as  the  depositions  of  ores  are  concerned,  the 
reactions  in  connection  with  underground  liquid  solutions  are 
by  far  the  more  important. 

The  water  of  rocks,  whether  at  ordinary  temperatures  and 
pressures  or  at  higher  temperatures  and  pressures,  may  take 
any  of  the  substances  with  which  it  comes  in  contact  into  solu- 
tion ;  may  deposit  substances  from  solution ;  may  combine  with 
substances  forming  hydrates,  as  in  the  case  of  many  of  the 
zeolites  or  of  limonite  from  hematite ;  may  part  with  its  hydro- 
gen in  exchange  for  bases,  and  especially  the  alkalies  and  alka- 
line earths,  thus  at  the  same  time  changing  the  composition  of 
the  rock  and  taking  the  bases  replaced  into  solution,  as  in  the 
change  of  enstatite  to  talc.  There  may  be  reactions  as  a  result 
of  different  substances  being  taken  into  solution  at  different 
times ;  there  may  be  reactions  as  a  result  of  different  solutions 
coming  together,  and  thus  mingling ;  there  may  be  reactions 
between  substances  in  solution  and  the  solid  material  with 
which  the  water  is  in  contact ;  there  may  be  reactions  as  a  result 
of  changing  temperature  and  pressure.  All  of  these  changes 
are  of  the  nature  of  chemical  action.  Therefore,  by  chemical 
action  of  underground  water  is  meant  the  taking  of  material 
into  solution,  the  deposition  of  material  from  solution,  the  inter- 
change between  materials  in  solutions,  the  interchange  between 
materials  in  solutions  and  adjacent  solids,  and,  finally,  the  inter- 
change of  the  adjacent  solid  particles.  But  this  last  reaction  is 
probably  accomplished  through  the  medium  of  a  separating 
film  of  water,  in  which  case  the  apparently  simple  reaction  is 
really  accomplished  by  transfers  between  the  solutions  and  solids. 

In  all  these  interchanges  the  materials  therefore  pass  through 
a  state  of  aqueous  solution,  and,  according  to  modern  ideas  of 
physical  chemistry,  the  salts  in  aqueous  solution  are  at  least 

*  "Outlines  of  General  Chemistry,"  by  W.  Ostwald  :  Translation  by  Walker, 
1895,  p.  292. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       319 

partly  separated  into  their  ions.  Their  properties  in  this  con- 
dition are  therefore  the  sum  of  the  properties  of  their  separated 
ions.  Indeed,  the  potency  of  water  as  an  agent  through  which 
metamorphism  may  take  place  is  due,  according  to  these  ideas, 
to  its  capacity  to  separate  substances  which  it  holds  in  solution 
into  their  free  ions.  In  this  power  of  ionization  water  exceeds 
all  other  solvents.  And  it  is  by  the  migration  of  these  free  ions 
that  the  interchanges  are  accomplished.  As  the  greater  por- 
tion of  underground  liquid  solutions  are  rather  dilute,  at  least 
where  somewhat  free  circulation  is  the  rule,  we  may  suppose  that 
the  salts  held  in  solution  are  largely  separated  into  their  ions,  and 
therefore  these  free  ions  are  ever  ready  for  chemical  reactions. 

Also  water  reacts  upon  the  salts  it  holds  in  solution  by  hy- 
drolitic  dissociation,  producing  free  acids  and  hydrates  of  the 
bases.  This  process  is  especially  important  with  the  salts  of 
the  weak  acids.*  The  dominant  acids  of  nature  are  the  very 
weak  acids  silicic  and  carbonic ;  and,  therefore,  hydrolitic  dis- 
sociation is  very  important.  The  silicates  of  the  alkalies  in 
dilute  solutions  are  practically  completely  decomposed,  the  re- 
sult being  the  liberation  of  free  silicic  acid  and  hydrates  of  the 
alkalies,  as  shown  by  Kahlenberg  and  Lincoln,  f  The  carbon- 
ates of  the  alkalies  are  also,  to  a  considerable  extent,  similarly 
dissociated. 

Underground  Aqueous  Solutions. — The  quantity  of  a  solid 
which  can  be  dissolved  in  liquid  depends  upon  the  number 
and  nature  of  the  compounds  present,  upon  the  pressure,  and 
upon  the  temperature. 

When  a  solid  salt  is  placed  in  liquid,  it  forms  a  homogeneous 
mixture  of  salt  and  liquid.  This  statement  applies  to  all 
natural  compounds, — that  is,  the  minerals  of  nature  are  salts 
which  are  soluble  in  water.  No  substance  is  wholly  insoluble 
in  the  underground  waters,  even  at  ordinary  temperatures  and 
pressures.  This  statement  applies  alike  to  quartz  and  the  most 
refractory  silicates.  Under  surface  conditions,  the  etching  of 
quartz  grains  is  evidence  of  the  first  statement,!  and  the  uni- 


*  "Theoretical  Chemistry,"  by  W.  Nernst,  1895,  p.  660. 

t  "Solutions  of  Silicates  of  the  Alkalies,"  by  Louis  Kahlenberg  and  A.  T. 
Lincoln,  Journ.  Phys.  Chem.,  vol.  ii.,  1898,  p.  89. 

t  "Solution  of  Silica  Under  Atmospheric  Conditions,"  by  C.  W.  Hayes,  Bull 
Geol.  Soc.  Am.,  vol.  viii,  1897,  pp.  213-220. 


320      SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

versa!  decomposition  and  partial  solution  of  the  silicates  is  evi- 
dence of  the  second ;  and  in  the  lower  zone  of  water  circulation 
the  solution  of  quartz  and  the  refractory  silicates  may  be  com- 
pletely accomplished,  as  in  the  case  of  the  Calumet  and  Hecla 
conglomerates,  many  of  the  bowlders  of  which  have  been  com- 
pletely dissolved  and  their  spaces  taken  by  copper. 

The  quantity  of  material  which  may  be  dissolved  in  any  case 
under  definite  conditions  has  a  limit.  When  this  limit  is 
reached  the  solution  is  saturated.  This  limit  depends  upon 
pressure  and  upon  temperature. 

The  Relations  of  Solution  and  Temperature. — The  relations 
of  temperature  and  solution  have  two  phases ;  (1)  the  speed  of 
the  reaction,  and  (2)  the  quantity  of  material  which  may  be 
held  in  solution. 

(1)  The  speed  of  solution  is  greatly  increased  by  rise  of  tem- 
perature.*    A  slight  increase  in  temperature  may  increase  the 
rate  of  solution  out  of  all  proportion  to  the  absolute  change  in 
temperature.     At  temperatures  above  100°  C.,  and  especially 
above  185°  C.,  the  activity  of  water  may  increase  to  an  amaz- 
ing degree.      The  rapid  solution  of  glass  by  Barusf  at  tem- 
peratures above  185°  C.  illustrates  this.     At  any  temperature 
solution  will  continue  until  the  point  of  saturation  is  reached. 
However,  it  is  clear  that  this  state  will  be  attained  at  high  tem- 
peratures in  but  a  small  fraction  of  the  time  required  at  low 
temperatures.     For  instance,  to  saturate  an  underground  solu- 
tion with  the  refractory  silicates  or  sulphides  at  ordinary  tem- 
peratures might  require  months  or  even  years,  while  to  saturate 
them   at  temperatures  above  185°  C.  might  require  only  an 
equal  number  of  minutes,  or  at  most  hours.     The  capacity  of 
water  for  action  at  high  temperatures  combined  with  pressure, 
considered  below,  is  adequate  to  explain  the  complete  recrys- 
tallization  of  great  volumes  of  natural  glass  and  crystallized 
rocks. 

(2)  The  effect  of  temperature  upon    quantity  of  material 
which  may  be  held  in  solution  does  not  admit  of  a  simple  gen- 


*  "Theoretical  Chemistry,"  by  W.  Nernst  Translated  by  C.  S.  Palmer,  Lon- 
don, 1895,  p.  568. 

|  "  Hot  Water  and  Soft  Glass  in  their  Thermo-dynamic  Kelations,"  by  C.  Barus. 
Am.  Journ.  Sci.,  4th  series,  vol.  ix.,  1900,  pp.  167-168. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.      321 

eral  statement.*  For  most  substances  moderate  increase  of 
temperature  gives  greater  capacity  for  solutions ;  but  for  many 
substances  there  exists  a  temperature  at  which  there  is  the 
maximum  capacity  for  solution,  and  the  amount  of  material 
which  may  be  held  in  solution  at  higher  and  lower  temperatures 
is  less  than  this  maximum.  For  various  substances  this  max- 
imum capacity  for  solution  lies  between  60°  C.  and  140°  C., 
and  for  many  substances  it  is  probably  below  200°  C.  It  there- 
fore follows  in  underground  solutions  that  a  general  statement 
cannot  be  made  as  to  how  change  of  temperature  may  affect 
solubility.  However,  it  is  highly  probable  that  up  to  tempera- 
tures of  100°  C.,  and,  therefore,  to  depths  of  3000  meters,  in- 
crease of  temperatiire  increases  the  average  capacity  of  under- 
ground water  to  hold  material  in  solution.  It  may  be  probable 
that  the  average  capacity  of  underground  water  may  increase 
to  temperatures  considerably  above  100°  C.,  and,  therefore,  to 
depths  greater  than  3000  meters.  But  when  water  passes  down- 
ward to  the  deeper  parts  of  the  zone  of  fracture  the  increase  in 
temperature  may  lessen  the  average  capacity  for  holding  mate- 
rial in  solution,  provided  the  joint  effect  of  pressure  be  barred. 
The  Relations  of  Solution  and  Pressure. — In  general,  the  vol- 
ume of  the  solvent  plus  that  of  the  salt  is  greater  than  that  of 
the  solution.  For  a  given  quantity  of  the  solution  the  con- 
traction is  greater  the  more  of  the  solvent  is  used.f  In  some 
cases,  however,  the  volume  of  the  salt  and  solvent  is  less  than 
that  of  the  solution,  or  expansion  results  from  dissolving  the 
solid.  Sal  ammoniac  in  water  is  an  illustration  of  this  case. 
From  the  foregoing  relations  we  obtain  a  rule  as  to  the  rela- 
tions of  pressure  to  solubility.  J  In  the  common  case  in  which 
the  volume  of  the  solution  is  less  than  that  of  solvent  and  salt, 
pressure  increases  solubility ;  for  in  that  case  solution  tends  to 
bring  the  molecules  nearer  together  and  works  in  conjunction 
with  the  pressure.  In  the  reverse  case,  that  in  which  the  vol- 
ume of  the  solution  is  greater  than  that  of  solvent  and  salt,  pres- 
sure decreases  the  solubility,  the  reason  being  the  reverse  of 
that  of  the  previous  case. 

*  "  Solutions,"  by  W.  Ostwald.     Translated  by  M.  M.  P.  Muir,  London,  1891, 
pp.  55-77. 

f  "Solutions,"  cit.,  p.  82. 

t  "  Theoretical  Chemistry,"  by  W.  Nernst,  1895,  p.  567. 


322       SOME   PRINCIPLES    CONTROLLING   DEPOSITION    OP    ORES. 

It  is  well  known  that  the  solubility  of  calcium  carbonate  and 
some  other  carbonates  is  increased  by  pressure.*  It  is  a  fair 
inference  from  Barus'  work  that  the  solubility  of  the  silicates 
is  also  increased  by  pressure.  Barusf  found  that  when  soft  glass 
is  dissolved  in  water  at  temperatures  above  210°  C.,  the  volume 
is  20  to  30  per  cent,  less  than  the  two  separately.  This  glass 
was  one  which  contains  alkalies,  alkaline  earth  and  lead,  and, 
therefore,  is  somewhat  similar  in  composition  to  many  natural 
silicates.  The  solubility  of  many  other  salts,  besides  the  car- 
bonates and  silicates,  occurring  underground  is  increased  by 
pressure.  While,  therefore,  pressure  may  lessen  the  solubility 
of  some  natural  salts,  in  the  majority  of  the  complex  under- 
ground solutions  the  volume  of  the  solution  is  less  than  that  of 
the  salts  and  solvent  separately ;  and,  therefore,  the  total  of  the 
salts  in  solution  is  generally  increased  by  pressure. 

It  has  been  pointed  out  that  in  the  lower  part  of  the  zone  of 
fracture  increase  in  temperature  with  depth  may  exceptionally 
lessen  the  average  amount  which  may  be  held  in  solution,  but  in- 
creasing pressure  with  increasing  depth  promotes  solubility. 
The  quantitative  values  of  these  two  elements  are,  however, 
unknown,  and  no  positive  statement  can  be  made  as  to  whether 
the  increasing  temperature  and  pressure  combined  in  passing 
to  the  lower  part  of  the  zone  of  fracture  increases  or  decreases 
the  capacity  of  underground  water  for  solution.  However,  it 
is  clear  that  to  very  considerable  depths,  that  is,  to  3000  meters 
or  more,  the  joint  effect  of  the  temperature  and  pressure  factors 
is  to  increase  the  average  capacity  for  solution. 

Precipitation — After  a  number  of  chemical  substances  are 
brought  together,  and  especially  when  they  are  united  by  a 
solvent,  interactions  between  them  may  occur  which,  after  a 
time,  appear  to  cease.  When  the  conditions  have  become  such 
that  there  is  no  increase  or  decrease  in  the  amount  of  any  one 
of  the  chemical  compounds,  the  system  is  in  a  condition  of 
chemical  equilibrium.  J  The  interaction  may  result  in  the  pre- 
cipitation of  compounds. 

*  «  Gold-quartz  Veins  of  Nevada  City  and  Grass  Valley,  California,"  by  W. 
Lindgren.  17th  Ann.  Report  U.  S.  Geol.  Survey,  1895-96,  pt.  ii.;  1896,  pp.  176-178. 

f  "  Hot  Water  and  Soft  Glass  in  their  Thermo-dynamic  Kelations,' '  by  C.  Barus. 
Am.  Journ.  Sci.,  4th  series,  vol.  ix.,  1900,  p.  173. 

J  Nernst,  tit.,  pp.  355-356. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OP    ORES.      323 

Since  the  separation  of  material  from  solution  in  under- 
ground waters  is  of  the  utmost  importance,  it  is  necessary  to 
consider  the  conditions  under  which  precipitation  takes  place. 
It  is  clear  that  the  necessary  condition  for  precipitation  is 
supersaturation ;  for  if  a  solution  be  sufficiently  supersaturated 
some  of  the  material  must  be  thrown  down,  or  be  precipitated. 

Supersaturation  and  consequently  precipitation  may  result  in 
various  ways,  of  which  the  following  are  the  more  important: 
(1)  By  change  in  temperature,  (2)  by  change  in  pressure,  (3)  by 
reactions  between  aqueous  solutions,  (4)  by  reactions  between 
liquid  solutions  and  solids,  and  (5)  by  reactions  between  gases 
and  solutions  or  solids,  or  both. 

1.  Precipitation  by  Change  in  Temperature. — Change  in  tem- 
perature is  the  rule  for  underground  circulating  waters.  The 
waters  which  are  passing  to  lower  levels  are  upon  the  average 
becoming  warmer.  Waters  which  are  rising  to  higher  levels 
are  upon  the  average  becoming  colder.  Also,  there  are 
changes  of  temperature  both  positive  and  negative  due  to 
varying  local  conditions. 

If  the  temperature  of  a  saturated  solution  changes  in  a  direc- 
tion adverse  to  solution,  it  tends  to  become  supersaturated.  If 
crystals  of  the  solid  in  solution  are  present,  and  this  is  usually 
the  case  with  underground  solutions,  considerable  supersatura- 
tion does  not  occur ;  for  the  excess  of  salt  separates,  so  that  at 
any  given  temperature  equilibrium  is  nearly  retained  by  con- 
tinuous adjustment. 

It  has  already  been  seen  that  increase  of  temperature  to  100° 
C.  or  more  promotes  solution,  and  decrease  of  temperature  from 
100°  C.  or  more  causes  supersaturation,  and  therefore  precipi- 
tation. One  would,  therefore,  expect  that  descending  waters 
which  are  increasing  in  temperature  are,  upon  the  whole,  con- 
stantly taking  additional  material  into  solution,  at  least  to  a 
depth  of  3000  meters,  and  that  waters  ascending  above  this 
level  which  are  becoming  cooler  are  upon  the  whole  precipitat- 
ing material.  However,  this  statement  needs  various  qualifica- 
tions. As  a  consequence  of  the  action  of  igneous  rocks  and 
dynamic  action  temperatures  higher  than  the  normal  for  a  given 
depth  may  be  obtained.  While  these  temperatures  may  be  so 
high  as  to  be  unfavorable  to  the  quantity  of  material  held  in 
solution,  they  are  very  favorable  to  rapid  solution.  Since  the 

21 


324       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

temperature  is  variable  which  causes  the  maximum  solution 
of  a  given  salt,  it  follows  that  as  water  passes  down  through 
the  middle  part  or  lower  parts  of  the  zone  of  fracture,  or  as  it 
becomes  somewhat  highly  heated  because  of  the  presence  of  ig- 
neous rocks  or  of  heat  produced  by  orogenic  movement,  that  the 
increase  of  temperature  may  induce  the  precipitation  of  some 
compounds,  and  favor  the  solution  of  additional  quantities  of 
other  compounds.  Therefore,  because  of  changing  temperature 
in  the  middle  and  lower  parts  of  the  zone  of  fracture,  and 
\vhere  igneous  rocks  are  present  or  earth  movements  have  oc- 
curred, there  is  selective  solution  and  precipitation.  However, 
in  the  normal  case  within  the  belt  of  which  we  have  most  exact 
information,  that  is,  the  upper  3000  meters  of  the  crust  of  the 
earth,  the  upward  course  of  water  is  likely  to  be  favorable  to 
precipitation.  (See  pp.  339-346.) 

2.  Precipitation  by  Change  in  Pressure. — It  has  been  seen  that 
where  waters  are  descending  the  pressure  is  constantly  becom- 
ing greater,  and  they  are  capable  of  taking  additional  material 
in  solution.     Where  waters  are  ascending  the  pressure  is  con- 
stantly becoming  less,  and  they  are,  therefore,  not  capable  of 
holding  so  much  material  in  solution.     Hence,  the  pressure 
effect  in  ascending  waters  is  to  promote  precipitation.      All 
of  these    statements    apply   to   the    average    complex   under- 
ground solutions.     Exceptional  cases  may  exist  where  the  re- 
verse effect  occurs. 

3.  Precipitation  by  Reactions  between  Aqueous  Solutions. — 
Physical  chemistry  holds  that  when  solutions  containing  various 
salts  are  mixed,  the  resultant  solution  will  contain  all  the  salts 
and  ions  which  can  be  made  by  the  various  combinations  of  their 
positive  and  negative  factors.     In  any  given  case  there  is  a  con- 
stant relation  between  the  amount  of  a  salt  which  can  be  held 
in   solution  and  the  number  of  free  ions  of  that  salt  which 
balance  each  other,  and  upon  this  fact  are  based  the  laws  of 
precipitation  from  solutions. 

The  laws  of  chemical  precipitation  from  aqueous  solutions 
are  somewhat  complex,  and  cannot  be  here  fully  summarized. 
So  far  as  present  purposes  are  concerned,  the  old  statement  of 
chemistry  will  suffice.  When  solutions  of  two  or  more  kinds 
are  mingled,  if  a  compound  or  compounds  can  form  which  are 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       325 

insoluble  in  the  liquids  present,  this  will  take  place  and  pre- 
cipitation will  follow.* 

The  most  important  case  of  precipitation  in  nature  is  that 
resulting  from  the  mingling  of  aqueous  solutions  of  solids. 

Another  case  of  precipitation  occurring  in  nature  results  from 
mixing  solutions,  one  of  which  contains  a  gas.  Perhaps  the 
most  important  case  of  this  kind  is  the  mixing  of  a  solution 
containing  oxygen  with  one  containing  salts  of  iron  protoxide. 
As  a  result  of  this,  the  salts  will  be  changed  from  ferrous  to 
ferric,  and  the  iron  in  latter  precipitated  either  as  a  sesquioxide 
or  hydrosesquioxide.  In  the  latter  case  hydration  occurs  simul- 
taneously with  the  oxidation. 

4.  Precipitation  by  Reactions  between  Liquid  Solutions  and 
Solids. — A  very  important  underground  reaction  is  that  be- 
tween the  solutions  and  the  adjacent  solid  materials.  Ordi- 
narily in  this  case  a  portion  of  the  solid  material  is  taken  into 
solution  and  a  portion  of  the  material  before  held  in  solution 
is  deposited.  This  principle  may  be  illustrated  by  the  labora- 
tory experiment  in  which  metallic  iron  is  placed  in  a  solution 
of  a  copper  salt,  for  instance  copper  sulphate.  The  iron  goes 
into  solution  as  sulphate  and  metallic  copper  is  precipitated. 
An  excellent  case  illustrating  precipitation  from  solution  in 
nature,  one  of  the  most  fundamental  importance,  is  the  almost 
immediate  partial  substitution  of  magnesium  for  the  calcium 
of  shells  and  corals  by  the  sea-waters. 

In  order  that  crystals  in  a  solvent  shall  grow,  it  is  necessary 
that  the  solutions  shall  be  saturated  or  supersaturated  at  the 
immediate  place  of  crystal  growth.  Since,  underground,  there 
is  always  a  superabundance  of  solid  material  present  as  compared 
with  the  amount  of  water,  we  may  suppose  that  at  a  moderate 
depth  below  the  surface,  and  especially  in  the  smaller  spaces 
where  movement  is  slow,  the  solutions  are  often  saturated.  It 
is  a  well-known  fact  that  under  conditions  of  saturation,  with  a 
superabundance  of  solid  material,  the  larger  crystals  grow  at  the 
expense  of  the  smaller  ones,  and  that  this  process  goes  on  more 
rapidly  in  proportion  as  the  temperature  is  high  and  the  pres- 
sure is  great.  This  principle  is  taken  advantage  of  in  the 

*  For  a  more  exact  statement  of  the  principles  of  precipitation  see  the  various 
treatises  on  physical  chemistry.  A  simple  statement  of  the  laws  of  precipitation 
is  given  byC.  F.  Tolman,  Journ.  of  Geol.,vol.  vii. ,  1899,  pp.  587-591. 


326      SOME    PRINCIPLES   CONTROLLING    DEPOSITION    OF    ORES. 

chemical  laboratory  in  the  production  of  a  coarse  precipitate 
before  filtration  by  boiling  or  other  means,  the  finer  particles 
of  the  precipitate  being  dissolved  and  the  coarser  ones  being 
enlarged  at  their  cost. 

5.  Precipitation  by  Reactions  between  Gases  and  Solutions, 
and  Solids. — The  reactions  between  gases  and  liquid  solutions 
and  solids  involve  matter  in  all  its  three  forms.  The  laws  of  their 
mutual  interactions  are  very  complex,  and  they  cannot  here  be 
taken  up.  But  for  the  present  purpose  it  may  be  said  that  the 
result  of  the  mixture  of  gases,  liquid  solutions  and  solids,  may 
result  in  the  precipitation  of  a  substance  from  solution.  The 
most  common  active  gases  present  underground  are  carbon 
dioxide,  hydric  sulphide,  and  oxygen.  The  action  of  hydric 
sulphide  upon  a  solution  may  throw  down  a  sulphide  of  a  metal; 
the  oxidizing  action  of  oxygen  may  result  in  precipitation,  as 
in  the  case  of  peroxidation  of  iron.  Furthermore,  the  action 
of  the  gases  and  liquid  solutions  may  together  result  in  the  ab- 
straction of  substances  from  the  solid  compounds  and  the  pre- 
cipitation of  them,  or  parts  of  them,  elsewhere.  The  combined 
action  of  gases,  liquids  and  solids  is  more  common  in  the  belt 
of  weathering  than  elsewhere  (See  pp.  327-329.) 

THE  GENERAL  GEOLOGICAL  WORK  OF  UNDERGROUND  WATERS. 
It  has  been  seen  that  the  geological  work  of  underground 
waters  is  dependent  on  many  factors.  Some  of  these  are  the 
limitation  in  depth  by  the  zone  of  fracture,  the  nature  of  the 
openings  in  the  rocks,  the  rapidity  of  the  flowage,  the  char- 
acter of  the  materials  through  which  the  waters  flow,  the  char- 
acter of  the  substances  it  may  carry  in  solution,  the  pressure, 
and  the  temperature.  Of  these  many  factors,  two  are  ever 
working  together  according  to  very  definite  laws.  These 
are  pressure  and  temperature.  Both  increase  with  depth, 
and  therefore  greatly  promote  the  activity  of  deep  under- 
ground waters.  However,  of  all  of  these  varying  factors, 
varying  temperature  is  the  one  which  is  of  incomparably  the 
greatest  importance.  High  temperature  ordinarily  results  from 
depth  of  penetration ;  but  it  has  been  pointed  out  that  it  may 
result  from  various  other  causes,  of  which  chemical  action, 
mechanical  action  and  the  presence  of  intrusive  igneous  rocks 
are  the  more  important.  The  capacity  which  water  has  for 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       327 

taking  and  holding  various  relatively  insoluble  compounds  in 
solution  increases  as  the  temperature  increases,  to  100°  C.  or 
more.  The  velocity  of  chemical  reactions  increases  enormously 
with  increase  of  temperature.  Not  only  is  high  temperature 
favorable  to  geological  work  because  of  the  chemical  activity 
of  the  water,  but  high  temperature  greatly  decreases  its  viscosity, 
and  this,  as  already  explained,  is  favorable  to  depth  of  pene- 
tration and  flowage  through  minute  openings.  Since  the  tem- 
perature changes  of  underground  water  are  commonly  depend- 
ent upon  depth,  the  vertical  component  of  the  movement  of 
underground  water  is  ordinarily  far  more  important  in  geo- 
logical work  than  the  longer  horizontal  component. 

Division  of  the  Zone  of  Fracture  into  a  Belt  of  Weathering  and  a 
Belt  of  Cementation. 

So  far  as  the  work  of  underground  water  in  the  production 
of  ore-deposits  is  concerned,  the  zone  of  fracture  may  be  divided 
into  two  belts  :  (1)  an  upper  belt  of  weathering,  and  (2)  a  lower 
belt  of  cementation.  The  belt  of  weathering  extends  from  the 
surface  to  the  level  of  groundwater,  and  for  a  variable  distance 
into  the  sea  of  underground  water.  The  belt  of  cementation 
extends  from  the  bottom  of  the  belt  of  weathering  to  the  bot- 
tom of  the  zone  of  fracture. 

In  the  belt  of  weathering  various  gases  are  present,  of  which 
carbon  dioxide  and  oxygen  are  the  more  important.  With  these 
are  a  great  variety  of  solutions  and  the  greatest  possible  va- 
riety of  solids.  The  reactions  in  the  belt  of  weathering,  there- 
fore, involve  gases,  liquids  and  solids.  Furthermore,  in  this 
.belt  we  have  the  complicated  action  of  organic  bodies  upon 
inorganic  bodies.  These  organic  compounds  vary  in  magni- 
tude from  the  smallest  bacteria  to  large  trees,  which  act  both 
while  alive  and  dead.  It  is,  therefore,  clear  that  the  chemical 
reactions  in  the  belt  of  weathering  are  of  an  extraordinarily 
complex  character.  Only  the  more  important  of  them  will  be 
considered.  The  dominant  ones  are  carbonation,  hydration, 
oxidation  and  solution. 

The  process  of  carbonation  takes  place  upon  a  most  exten- 
sive scale  in  the  belt  of  weathering,  producing  abundantly  car- 
bonates of  the  alkalies,  alkaline  earths  and  iron,  and  less  abund- 
antly carbonates  of  other  metals.  "Where  vegetation  is  absent 


328       SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

the  air  in  the  soil  contains  only  a  small  amount  of  carbon  diox- 
ide, but  where  vegetation  is  abundant  and  is  decaying  upon  a 
large  scale,  the  carbon  dioxide  in  the  soil  is  from  15  to  100 
times  more  abundant  than  in  air ;  hence,  in  the  process  of  car- 
bonation  the  presence  of  vegetation  is  of  fundamental  import- 
ance. The  dominant  compounds  upon  which  the  process  of 
carbonation  acts  are  the  silicates.  In  the  carbonation  of  the 
silicates  the  silica  separates  as  silicic  acid.*  Since  the  quan- 
tity of  silicates  decomposed  by  carbonation  is  very  great,  the 
amount  of  silicic  acid  liberated  is  enormous.  This  passes  into 
solution,  and,  as  explained  below,  is  transferred  to  the  belt  of 
cementation. 

Next  in  importance  to  carbonation  is  hydration.  While  hy- 
dration  is  usual  in  the  belt  of  weathering,  under  some  con- 
ditions, and  especially  those  of  great  aridity  and  high  temper- 
ature, dehydration  may  occur. 

Oxidation  is  also  very  general  in  the  belt  of  weathering,  but 
deoxidation  may  occur  in  regions  of  very  luxuriant  vegetation, 
where  there  is  an  unusually  large  amount  of  reducing  material. 

If  the  compounds  formed  in  the  belt  of  weathering  all  re- 
mained in  situ,  the  volume  of  the  rocks  would  be  greatly  in- 
creased by  the  above  changes;  but  simultaneously  with  these 
reactions,  solution,  the  fourth  important  reaction  of  the  belt  of 
weathering,  is  taking  place  upon  a  great  scale.  The  quantity 
of  material  dissolved  is  more  than  sufficient  to  counterbalance 
the  increase  in  volume  due  to  the  chemical  changes,  and  conse- 
quently the  volume  of  the  rocks  continually  decreases.  In  con- 
sequence of  this  preponderance  of  solution  the  openings  of  the 
belt  of  weathering  tend  to  increase  in  size.  However,  this  is 
not  apparent  with  the  unconsolidated  materials  at  the  surface, 
for  gravity  brings  the  particles  together  as  fast  as  material  is 
dissolved ;  but  in  the  rocks  below  the  soils,  which  have  suf- 
ficient strength  to  support  themselves,  the  openings  are  widened. 
The  best  illustrations  of  rocks  with  enlarged  openings  are  the 
limestones. 

In  connection  with  the  chemical  changes  above  summarized, 
mechanical  action  is  continually  subdividing  the  material. 


*  ' '  Solutions  of  Silicates  of  the  Alkalies, "  by  L.  Kahlenberg  and  A.  T.  Lincoln. 
J&urn.  Phys.  Chem.,  vol.  ii.,  1898,  pp.  88-90. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       329 

In  general,  then,  in  the  belt  of  weathering,  disintegration, 
decomposition  and  solution  are  the  rules.  The  minerals  which 
remain  are  usually  few  and  simple ;  the  volume  of  the  rocks  is 
diminished ;  they  soften  and  degenerate ;  and  they  are  finally 
destroyed  as  coherent  solids. 

In  the  belt  of  cementation,  hydration,  carbonation,  oxidation, 
and  deposition  occur.  Hydration  and  deposition  are  the  char- 
acteristic reactions.  Carbonation  and  oxidation  are  subordin- 
ate. The  reactions  take  place  by  metasomatic  change  within 
many  of  the  original  minerals  and  by  deposition  of  material 
within  the  openings.  Many  of  the  minerals  produced  are 
strongly  hydrated.  Because  of  hydration  and  deposition  the 
volume  of  the  rocks  is  increased.  Cracks  and  crevices  produced 
by  mechanical  action,  such  as  those  of  faults,  joints,  bedding 
partings  and  fissility ;  and  the  openings  originally  present  in 
the  rocks,  such  as  pore-spaces  in  the  mechanical  sediments  and 
the  vacuoles  in  volcanic  rocks,  are  slowly  but  certainly  filled  by 
the  action  of  the  groundwater^  and  the  rocks  are  thus  cemented 
and  indurated.  This  process  may  be  called  construction. 

The  belts  of  weathering  and  cementation,  therefore,  contrast 
strongly.  In  the  former  solution  continually  takes  place;  in 
the  latter,  deposition;  in  the  former  we  have  disintegration, 
decomposition  and  softening;  in  the  latter  we  have  cementation 
and  induration;  in  the  former  the  volume  of  material  is  less- 
ened ;  in  the  latter  it  is  increased ;  in  the  former  the  character- 
istic chemical  reaction  is  carbonation ;  in  the  latter  it  is  hydra- 
tion. Therefore,  the  belt  of  weathering  is  characterized  by 
disintegration  and  decomposition,  carbonation,  hydration  and 
oxidation,  by  solution  and  decrease  of  volume.  The  belt  of 
cementation  is  characterized  by  cementation  and  induration,  by 
hydration,  by  deposition,  and  by  increase  of  volume. 

Migration  of  Material  from  the  Belt  of  Weathering  to  the  Belt  of 

Cementation. 

It  is  believed  that  the  material  dissolved  in  the  belt  of  weath- 
ering is  largely  deposited  in  the  belt  of  cementation.  Thus 
may  be  explained  the  steady  diminution  of  a  given  mass  of 
material  in  the  belt  of  weathering,  and  the  increase  in  mass  of 
the  material  in  the  belt  of  cementation.  Since  this  migration 


330       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

of  material  is  one  of  great  importance,  it  will  be  necessary  to 
consider  it  in  some  detail. 

As  a  result  of  the  horizontal  component  of  the  movement  of 
underground  water,  there  is  a  tendency  for  material  to  be  taken 
into  solution  and  to  be  abstracted  by  the  water.  The  longer 
the  horizontal  underground  course,  the  nearer  will  the  water 
approach  to  saturation  with  the  compounds  with  which  it  is  in 
contact,  because  of  the  time  factor.  If  the  journey  be  long,  the 
state  of  saturation  may  be  attained  at  an  early  stage,  after  which 
the  additions  and  subtractions  of  material  upon  the  average 
neutralize  each  other.  Throughout  the  j  ourney  there  are  various 
chemical  interactions.  There  may  be  solution  of  material  at  a 
certain  place  and  later  deposition  of  it  elsewhere ;  there  may 
be  interactions  between  the  solutions  and  solids ;  there  may  be 
interactions  between  the  mingled  solutions  from  different 
sources.  However,  these  reactions  do  not  change  the  end- 
result — that  is,  the  longer  the  horizontal  journey  the  richer  the 
solutions  become,  and  material  is  abstracted  until  the  point  of 
saturation  is  reached. 

Since  it  is  clear  that,  so  far  as  the  horizontal  movement  of 
underground  water  is  concerned,  the  effect  is  to  abstract  ma- 
terial, and  since  deposition,  with  consequent  cementation  and 
consolidation  rather  than  solution  is  a  general  fact  in  the  belt 
of  saturation,  we  conclude  that  this  result  must  be  due  to  the 
vertical  movement  of  the  water.  In  the  downward  journey  of 
the  water  from  the  surface  to  the  level  of  groundwater,  it  is 
continuously  taking  material  into  solution,  and  therefore  steadily 
contributes  an  increment  of  material  to  the  sea- of  underground 
water. 

After  the  water  reaches  the  level  of  groundwater,  movement 
does  not  cease.  Disregarding  the  lateral  movement,  the  sea 
of  underground  water  at  a  given  place  might  be  considered  as 
a  column  moving  downward  as  rapidly  as  the  increment  of 
groundwater  is  added  from  above.  However,  superimposed 
upon  this  vertical  movement  is  lateral  movement  which  carries 
it  to  some  point  where  upward  movement  is  taking  place. 
Therefore  the  amount  which  continues  downward  is  an  ever- 
decreasing  fraction  of  the  entire  amount  of  precipitation  which 
joins  the  sea  of  groundwater.  But  for  this  part  the  pressure 
and  temperature  steadily  increase,  and  the  capacity  of  the 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       331 

water  to  take  material  into  solution  steadily  changes.  One 
might  conclude  that  during  at  least  the  first  part  of  the  down- 
ward course  of  the  water  solution  was  occurring.  During  the 
upward  course  of  the  water,  pressure  and  temperature  steadily 
become  less,  and  one  might  conclude  that  for  at  least  the  latter 
part  of  the  upward  course  deposition  was  occurring.  How- 
ever, these  simple  statements  do  not  fully  cover  the  facts ;  for, 
as  already  pointed  out,  the  relations  of  temperature  and  pres- 
sure are  exceedingly  complex,  and  also  deposition,  cementa- 
tion and  consolidation  seem  to  be  general  facts  for  the  belt  of 
cementation. 

It  has  already  been  pointed  out  that  the  conditions  for  solu- 
tion are  very  favorable  in  the  downward  passage  of  water 
through  the  belt  of  weathering,  and  that  each  unit  of  water 
which  joins  the  belt  of  cementation  carries  with  it  in  solution  a 
certain  increment  of  material.  During  the  long-continued 
erosion  of  a  region  the  belt  of  weathering  at  any  given  time 
represents  the  residual  disintegrated  and  partly  decomposed 
material  then  above  the  level  of  groundwater.  Thus  the  belt 
of  weathering  is  steadily  progressing  downward.  The  forces 
of  weathering  are  continually  finding  new  material  at  the 
bottom  of  the  belt  upon  which  to  work.  Therefore,  as  denu- 
dation goes  on  there  is  ever  a  belt  of  a  certain  thickness  which 
contributes  material  to  the  belt  of  cementation  below.  Hence 
we  have  an  adequate  source  for  an  increment  continuously 
added  to  the  belt  of  cementation.-  If  this  increment  thus 
added  to  the  sea  of  underground  water  could  be  deposited 
throughout  its  course  in  the  belt  of  cementation,  there  would 
be  a  sufficient  cause  for  the  induration  of  this  belt. 

However,  according  to  one  of  our  fundamental  premises,  the 
quantity  of  water  which  emerges  by  seepage  or  through  springs 
to  the  surface  and  joins  the  run-off  must  be  equal  to  the 
amount  added  to  the  sea  of  groundwater  by  percolation.  The 
question  must  therefore  be  asked  as  to  the  relative  amounts  of 
materials  carried  to  the  sea  of  groundwater  by  percolation  and 
that  abstracted  from  it  by  the  ascending  waters.  To  this  ques- 
tion no  answer  based  upon  comparative  analyses  can  be  given. 
However,  the  general  deposition  and  consolidation  in  the  zone 
of  cementation  already  emphasized  seems  to  be  conclusive 
evidence  that  the  amount  of  material  contained  in  issuing 


332       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

water  is  not  so  great  as  that  which  joins  it  through  perco- 
lation. 

Of  the  substances  deposited  in  the  belt  of  cementation, 
quartz  is  undoubtedly  the  one  which  dominates  over  all  others. 
The  one  great  process  in  the  belt  of  cementation  is  silication. 
Next  in  abundance  to  the  quartz,  the  various  silicates  are  de- 
posited, and  especially  the  zeolites  and  chlorites.  Of  less  im- 
portance are  the  carbonates  of  the  alkaline  earths.  Still  less 
abundant  are  the  various  metalliferous  ores  and  associated 
gangue  minerals  not  of  the  classes  already  mentioned.  While 
these  subordinate  products  are  of  great  economic  importance, 
their  quantity  is  insignificant  as  compared  with  the  non-metal- 
liferous deposits. 

If  it  is  certain  that  the  one  great  process  of  the  belt  of 
cementation  is  silication ;  it  is  equally  certain  that  the  one  great 
process  in  the  belt  of  weathering  is  the  carbonation  of  the  sili- 
cates, thus  forming  carbonates  and  liberating  soluble  silicic  acid. 
Hence  it  is  highly  probable  that  silicic  acid  is  the  dominant  con- 
stituent contained  in  solution  in  downward  percolating  waters. 
Therefore  we  have  a  source  both  for  the  deposited  quartz  and 
for  the  process  of  silication  which  forms  the  silicates.  In 
another  place*  I  have  shown  that  one  of  the  deep-seated  domi- 
nating reactions  is  the  process  of  silication  of  the  carbonates 
or  the  substitution  of  silica  for  carbon-dioxide  with  the  simul- 
taneous liberation  of  carbon-dioxide.  This  process  takes  place 
at  moderate  depth,  especially  under  dynamic  conditions,  although 
it  is  especially  important  in  the  zone  of  rock-flowage.  The  car- 
bon-dioxide liberated  in  part  joins  the  underground  waters. 
Such  carbonated  waters  are  very  capable  of  taking  into  solution 
the  salts  of  the  metals,  and  particularly  the  salts  of  the  alkalies, 
alkaline  earths  and  iron.  The  solutions  which  reach  the  surface 
bear  as  their  more  abundant  compounds  the  carbonates  of  the 
alkalies,  alkaline  earths  and  iron.  With  these  are  also  other 
salts,  including  the  salts  of  the  valuable  metals.  Also  issuing 
waters  contain  other  acids  besides  carbonic  acid,  such  as  chlor- 
hydric,  sulphydric,  sulphuric  and  others. 

From  the  foregoing  it  appears  that  during  the  circulation  of 


*  "  Metamorphism  of  Bocks  and  Hock  Flowage,"  by  C.  E.  Van  Hise,  Bull.  O. 
S.  A.,  vol.  ix.,  1898,  p.  282. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       333 

water  in  the  belt  of  cementation  the  processes  of  precipitation 
and  solution  are  selective.  Quartz  and  silicates  are  the  dominant 
precipitates.  Carbonates  of  the  alkalies  and  alkaline  earths  are 
the  dominant  salts  which  join  the  run-off.  The  above  precipi- 
tations and  solutions  are  precisely  what  should  be  anticipated 
from  the  laws  of  chemical  action  already  given.  The  com- 
pounds which  upon  the  average  are  thrown  down  to  the  great- 
est extent,  are  those  which  are  least  soluble  and  most  abundant. 
The  compounds  which  are  retained  in  solution  to  the  greatest 
extent  are  those  which  are  most  soluble  and  least  abundant. 
However,  of  the  more  soluble  and  less  abundant  compounds  a 
portion  is  precipitated.  The  conditions  under  which  we  would 
expect  partial  precipitation  of  these  compounds,  at  least  for  the 
upper  3000  meters,  are  those  of  lessening  temperature  and 
pressure.  These  are  the  conditions  of  the  ascending  columns 
of  water.  It  has  already  been  seen  that  the  ascending  columns 
are  likely  to  be  the  main  water  channels.  Hence  is  explained 
the  frequent  precipitation  of  soluble  carbonates  of  the  alkaline 
earths  and  rare  metalliferous  ores  in  these  trunk  channels. 

It  is  not  supposed  that  the  above  furnishes  a  full  explanation 
of  the  cementation  of  the  entire  zone  of  fracture.  It  has  been 
pointed  out,  p.  329,  thathydration  is  perhaps  the  most  character- 
istic reaction  of  this  belt  and  that  hydration  results  in  expansion 
of  volume.  So  far  as  this  reaction  takes  place,  and  it  undoubt- 
edly occurs  on  a  most  extensive  scale,  this  would  tend  to  fill  the 
openings  and  thus  cement  and  consolidate  the  rocks  without 
reference  to  material  from  the  belt  of  weathering.  Thus,  for 
instance,  metasomatic  change  including  hydration  in  a  vesicular 
basic  igneous  rock  may  so  increase  the  volume  of  the  material 
as  to  completely  fill  the  vesicles  by  zeolites,  quartz,  and  other 
minerals  without  the  addition  of  any  material  from  an  extrane- 
ous source.  Which  of  the  two  factors,  material  from  the  belt 
of  weathering,  or  expansion  by  the  processes  of  metasomatism 
including  hydration,  is  the  more  important  in  filling  openings 
in  the  belt  of  cementation,  I  am  wholly  unable  to  state. 

Other  factors  also,  doubtless,  enter  into  the  cementation  of 
openings.  Some  of  these  have  already  been  mentioned.  These 
are  selective  solution  and  precipitation,  depending  upon  vary- 
ing temperature  and  pressure,  and  the  reaction  of  the  different 
solutions  upon  one  another.  Another  factor  which  is  probably 


334       SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

important  is  diffusion,  but  its  action  is  too  complex  to  be  taken 
up  in  this  general  paper. 

By  the  various  processes  of  cementation  the  larger  openings 
are  filled  with  deposits.  However,  where  one -of  these  contains 
metalliferous  ores  in  sufficient  quantity  to  be  of  service  to  man, 
many  thousands  are  filled  with  quartz,  calcite,  dolomite,  and 
other  gangue  minerals.  I  repeat  again  that  the  deposition  of 
the  ores  is  but  a  special  phase  of  a  general  geological  process 
of  great  consequence. 

PART  II.— APPLICATION   OF    PRINCIPLES   TO   ORE- 
DEPOSITS. 

The  general  discussion  in  Part  I.  is  believed  to  contain  in 
large  measure  the  philosophy  of  the  formation  of  ore-deposits 
by  underground  waters.  It  is  now  clearer  than  when  first  stated 
that  the  deposition  of  the  greatest  group  of  metalliferous  ores  is 
a  special  case  of  the  work  of  underground  water. 

There  have  been  endless  discussions  as  to  whether  ore-de- 
posits are  produced  by  descending,  lateral-secreting,  or  ascend- 
ing waters.  It  is  a  corollary  from  Part  I.  that  the  first  con- 
centration of  many  ore-deposits  is  the  result  of  descending, 
lateral-moving,  and  ascending  waters.  I  say  first  concentration; 
for  it  will  subsequently  appear  that  many,  if  not  the  majority, 
of  the  workable  ore-deposits  have  undergone  a  second  concen- 
tration. 

The  larger,  more  nearly  complete  idea  of  the  genesis  of  ore- 
deposits  comprises  all  of  the  old  ideas,  shows  that  instead  of 
being  contradictory,  as  supposed  by  many,  they  are  mutually 
supporting;  combined,  they  furnish  a  much  more  satisfactory 
theory  than  any  one  of  them  alone.  How  true  these  statements 
are  will  later  more  clearly  appear. 

In  the  first  stage  of  the  concentration  of  many  deposits  the 
waters  are  descending.  During  the  descent  they  are  widely 
dispersed  in  small  passages,  have  an  exceedingly  large  surface 
of  contact  with  the  rocks,  come  under  conditions  of  increasing 
temperature  and  increasing  pressure,  and  are  moving  slowly 
downward.  All  of  these  conditions  favor  solution  to  the  point 
of  saturation.  The  various  metalliferous  elements  present  in 
exceedingly  small  quantities  in  the  rocks,  as  well  as  many  other 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OP    ORES.      335 

compounds,  are  picked  up.  (See  pp.  319-322.)  This  follows  from 
the  law  of  physical  chemistry,  that  a  solution  will  hold  some 
part  of  all  of  the  elements  with  which  it  is  in  contact.  While 
deposition  as  a  whole  may  be  occurring  in  the  belt  of  cementa- 
tion, solution  of  the  ores  certainly  takes  place. 

The  waters  which  perform  the  first  work  in  the  genesis  of  ore- 
deposits  are  descending  waters. 

Superimposed  upon  the  downward  component  of  the  moving 
waters  is  a  lateral  component.  This  lateral  component,  com- 
bined with  the  vertical  component,  carries  water  sooner  or  later 
to  the  trunk  channels.  The  amount  of  water  taking  part  in 
the  lateral  movement  is  greatest  near  the  surface  of  ground- 
water,  and  from  that  surface  steadily  decreases  to  the  bottom 
of  the  zone  of  fracture.  It  has  been  explained  that  all  fissures 
and  other  openings  gradually  die  out  below  as  the  zone  of  rock- 
nowage  is  neared.  (See  pp.  288-291.)  Therefore,  for  a  given 
fissure,  the  waters  which  enter  it  do  so  from  the  side  or  top, 
not  from  the  bottom.  Furthermore,  the  water  does  not  enter 
the  fissure  at  a  single  place,  but  may  enter  at  numberless  points 
all  the  way  along  its  course,  from  the  deepest  parts  of  the 
fissure  to  the  surface.  Somewhere,  however,  the  water  which 
enters  a  fissure  must  flow  from  it.  This  place  may  be  at  the 
surface  of  the  ground  or  at  a  considerable  depth  below  the 
level  of  groundwater  (see  Fig.  6).  The  streams  entering  the  fis- 
sure at  high  levels  may  have  a  downward  component,  and  con- 
tribute water  abundantly.  Below  the  level  at  which  water 
escapes  laterally  from  a  channel  of  given  size,  the  water  con- 
tributed to  it  decreases  on  the  average  with  increase  of  depth, 
until  in  the  deeper  part  of  the  zone  of  fracture  the  contributions 
are  very  small.  Posepny*  calls  attention  to  the  generally  ob- 
served fact  of  the  decreasing  amount  of  laterally  contributed 
waters  as  depth  increases.  As  a  specific  instance  of  this,  he 
mentioned  the  Przibram  district,  in  which  the  water  which 
enters  the  fissures  below  a  depth  of  300  meters  is  so  small  as 
to  be  insignificant. 

"While  the  amount  of  water  laterally  entering  a  fissure 
steadily  decreases  from  near  its  top  to  the  bottom,  the  amount 

*  This  volume,  p.  242. 


336       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

of  mineral  material  per  unit  volume  in  all  probability  steadily 
increases  ;  for  the  waters  entering  at  a  low  level  take  a  longer 
journey  through  smaller  openings  and  at  higher  temperatures 
and  pressures  than  the  waters  entering  at  a  high  level.  There- 
fore it  is  clear,  if  the  rocks  with  which  the  deeper  water  comes 
in  contact  can  furnish  metalliferous  materials,  that  such  water 


FIG.  6. 


Ideal  Vertical  Section  of  the  Flow  of  Water  Entering  at  a  Number  of  Points 
on  a  Slope,  and  Passing  to  a  Valley  Below,  through  a  Homogeneous  Medium,  In- 
terrupted by  Two  Open  Vertical  Channels,  on  the  Slope  and  in  the  Valley  Re- 
spectively. 

will  be  heavily  loaded.  It  follows  from  this,  even  if  the 
amount  of  water  which  is  furnished  in  a  given  brief  time  to  a 
fissure  be  small,  that  such  water  may  furnish  from  the  country- 
rock  much  more  mineral  material  in  solution  than  sufficient 
to  entirely  fill  a  fissure  during  its  long  life.  This  is  evident 
from  the  following :  Water  issuing  at  the  surface  from  min- 
eral springs  generally  contains  more  than  1  part  of  silica  in 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       337 

100,000.*  If  it  be  premised  that  only  as  much  silica  be  de- 
posited as  issues  at  the  surface,  in  order  completely  to  fill  a 
fissure  it  would  be  necessary  only  to  suppose  that  the  amount 
of  water  which  enters  a  unit  length  of  a  fissure  is  100,000 
times  as  great  as  the  volume  of  a  unit  length  of  the  opening. 

We  now  understand  that  the  amount  of  water  entering  a 
fissure  decreases  from  the  level  of  groundwater  to  its  bottom, 
but  that  the  amount  of  mineral  matter  brought  into  the  fissure 
by  the  water  (but  not  necessarily  deposited)  increases  per  unit 
volume  from  top  to  bottom.  It  is,  therefore,  impossible  to 
make  a  general  statement  as  to  whether  more  mineral  material 
is  contributed  to  a  trunk  channel  in  its  upper  portion  or  in  its 
lower  portion.  Doubtless  this  varies  in  different  cases.  Other 
conditions  than  amount  of  water  or  depth  may  be  controlling 
factors  in  this  respect.  For  instance,  if  igneous  rocks  be  in- 
truded at  high  or  low  levels  only,  the  presence  of  the  igneous 
rocks  may  furnish  conditions  which  determine  the  amount  of 
metalliferous  material  contributed  by  the  waters. 

While  the  foregoing  paragraphs  imply  that  the  lateral  mov- 
ing waters  are  also  downward  moving,  this  is  meant  only  as  a 
general  rule.  The  lateral  movement  may  be  accompanied  by 
no  downward  movement.  Not  only  this,  but  lateral  movement 
may  be  accompanied  by  an  upward  component.  Indeed,  this 
is  believed  to  be  very  frequently  the  case,  especially  so  far  as 
the  main  branch  streams  in  the  deeper  parts  of  the  zone  of 
fracture  are  concerned.  In  so  far  as  there  is  an  upward  compo- 
nent in  these  branch  streams,  the  reactions  which  obtain  are 
the  same  as  those  of  the  trunk  channels  to  be  considered 
below. 

From  the  foregoing,  it  appears  that  ores  are  carried  to  trunk 
channels  by  laterally  moving  waters.  Lateral  secretion  is  therefore 
an  essential  step  in  the  first  concentration  of  ore-deposits,  although 
I  use  the  term  lateral  secretion  in  a  broader  sense  than  did 
Sandberger. 

We  have  now  reached  the  place  where  the  ore-deposits 
themselves  are  found.  As  already  noted,  these  mainly  occur 
in  the  more  continuous  larger  openings.  These  openings  are 


*  "  Lists  and  Analyses  of  the  Mineral  Springs  of  the  United  States,"  by  A.  C. 
Peale,  Bull  U.  S.  GeoL  Surv.,  No.  32,  1886. 


338      SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OP    ORES. 

occupied  by  the  trunk  streams  of  circulating  waters,  and 
therefore  the  journey  of  the  water  is  in  the  latter  part  of  its 
course.  Hence  these  trunk  streams,  as  has  already  been 
shown  (p.  3 16),  have  in  general  an  upward  rather  than  a  down- 
ward vertical  component.  The  waters  reaching  the  trunk 
channel  at  any  point  immediately  begin  their  ascent.  At  any 
given  cross-section  of  a  channel  there  must  pass  all  of  the 
water  contributed  below.  This  amount  at  great  depth  has 
already  been  seen  to  be  small.  From  a  small  amount,  the 
waters  steadily  increase  in  volume  to  the  point  where  they 
begin  to  escape  laterally  from  a  trunk  channel  (see  Fig.  .6). 
Hence  from  a  trunk  channel  of  a  definite  size  the  circulation  is 
slow  below  and  increases  in  speed  above.  Near  the  bases  of 
the  channels  from  which  the  Mammoth  Hot  Springs  and  geysers 
of  the  Yellowstone  Park  issue  the  amount  of  water  contributed 
may  be  small,  and  the  movement  of  the  water  may  be  exceed- 
ingly slow.  Even  if  true,  as  held  by  some,  that  rapid  movement 
of  water  is  unfavorable  to  deposition  of  ores,  it  is  wholly  possible 
at  moderate  depths  and  especially  in  the  deeper  parts  of  a 
channel  from  which  the  flow  at  the  surface  is  rapid,  that  the 
conditions  are  those  of  slow  movement  and  rapid  precipitation 
of  ore-deposits. 

As  the  water  passes  upward,  the  variety  of  solutions  as  well 
as  the  amount  increases;  for  each  stream  differs  in  its  salts 
from  any  other,  since  no  two  streams  can  possibly  have  had 
exactly  similar  histories.  Moreover,  the  character  of  the  wall- 
rock  may  vary  from  place  to  place.  The  pressure  and  the 
temperature  are  also  lessening.  These  conditions  are  favorable 
to  precipitation.  Therefore,  many  ores  in  their  first  concentration 
are  precipitated  by  ascending  waters. 

It  is  now  clear  that  a  satisfactory  account  of  the  genesis  of 
ores  includes  ascending  waters.  By  the  ascending  waters  many 
ores  in  their  first  concentration  are  actually  precipitated,  and 
thus  the  emphasis  which  has  been  placed  upon  this  part  of  the 
work  of  circulating  waters. 

The  broader  statement  of  the  genesis  of  a  great  class  of  ore- 
deposits  is  that  the  water  after  penetrating  the  earth  is  widely 
scattered  in  contact  with  rocks  in  innumerable  minor  openings. 
These  waters  travel  downward  with  steadily  increasing  pressure 
and  temperature.  They  take  up  the  constituents  of  the  ore- 


SOME    PRINCIPLES   CONTROLLING    DEPOSITION   OP    ORES.      339 

deposits.  The  downward  movement  of  the  waters  has  super- 
imposed upon  it  a  lateral  component,  as  a  result  of  which  the 
waters  are  carried  to  the  larger  openings.  During  this  process, 
also,  the  waters  continue  to  take  material  into  solution.  In 
the  larger  openings  where  the  waters  are  congregated  they  are 
upon  the  average  at  first  ascending  with  decreasing  tempera- 
ture and  pressure,  and  there  the  ores  are  precipitated. 

Of  course,  from  this  statement  it  is  not  meant  to  imply  that 
materials  are  not  deposited  by  descending  and  lateral  moving 
waters,  nor  that  materials  are  not  dissolved  by  ascending 
waters.  Indeed,  it  is  certain  that  solution  and  precipitation 
are  taking  place  at  all  times  throughout  the  entire  course  of 
all  the  branches  of  the  underground  circulation.  This  is  a 
necessary  consequence  of  the  laws  of  physical  chemistry.  It 
is  only  meant  to  imply  that  in  the  first  concentration  of  one 
class  of  ore-deposits,  solution  so  far  as  the  ores  are  concerned 
is  the  rule  for  the  descent  and  deposition  for  the  ascent, 
although  there  is  no  doubt  that  there  are  many  local  excep- 
tions to  this. 

It  is  of  course  understood  that  the  underground  circulation 
in  any  actual  instance  will  be  much  more  complex  than  that 
given  in  the  simple  ideal  case  which  has  been  considered.  This 
part  of  the  subject  will  be  developed.  For  instance,  it  is  cer- 
tain that,  in  the  same  mineral-bearing  area,  immediately  adja- 
cent trunk-channels  may  have  had  very  different  histories.  This 
is  especially  well  shown  by  the  deposits  of  Butte,  Montana, 
where  there  are  two  parallel  main  zones  of  mineralization,  only 
a  short  distance  apart,  the  mineral  wealth  of  one  of  which  is 
mainly  copper,  while  that  of  the  other  is  mainly  silver.*  Many 
of  the  other  special  factors  which  modify  the  simple  general 
statement  above  given  are  discussed  on  pp.  393—421. 

THE  PRECIPITATION  OF  ORES  BY  ASCENDING  WATERS. 

The  precipitation  of  ores  in  the  trunk-channels  by  ascending 
waters  is  of  so  much  importance  in  the  concentration  of  ores 
that  this  process  needs  further  consideration.  The  precipita- 
tion results  from  the  various  principles  given  pp.  322-326. 

*  "  Notes  on  the  Geology  of  Butte,  Montana,"  by  S.  F.  Emmons.    Trans.,  xvi., 
54,  1888. 

22 


340       SOME    PRINCIPLES    CONTROLLING   DEPOSITION   OF    ORES. 

Precipitation  by  Decrease  of  Temperature  and  Pressure. 

The  general  relations  of  solution  and  precipitation  as  a 
consequence  of  varying  temperature  and  pressure  have  been 
considered  pp.  323-325.  Where  the  increment  of  temperature 
is  normal,  it  has  been  seen  that  decreasing  temperature  and 
pressure  resulting  from  the  ascension  of  waters  from  at  least  a 
depth  of  3000  meters  are  favorable  to  precipitation.  Further- 
more, the  same  statement  holds  even  if  the  increment  of  tem- 
perature is  greater  than  normal,  provided  the  temperature  does 
not  greatly  exceed  100°  C.,  and  cases  in  which  water  issues  at 
the  surface  at  such  temperatures  are  very  rare.  Moreover, 
probably  decreasing  pressure  and  temperature  with  rising  so- 
lutions at  depths  greater  than  3000  meters  are  favorable  to  pre- 
cipitation. Since  it  has  just  been  shown  that  ascending  waters 
are  likely  to  be  in  trunk-channels,  these  are  the  places  where 
lessening  temperature  and  pressure  are  most  likely  to  produce 
precipitates.  Therefore  the  openings  of  faults,  joints  and  bed- 
ding partings  and  the  more  open  places  in  porous  sandstones, 
conglomerates  and  amygdaloids,  are  likely  to  have  material 
precipitated  in 'them  as  a  consequence  of  lessening  temperature 
and  pressure. 

When  one  attempts  to  apply  these  general  statements  to  spe- 
cific salts,  we  find  experimental  data  lacking.  It  is  undoubt- 
edly the  case  that  decreasing  temperature  and  pressure  are  much 
more  influential  in  the  precipitation  of  some  salts  than  of  others ; 
and  that  with  a  few  salts  decreasing  temperature  and  pres- 
sure are  favorable  to  solution.  Until  experimental  work  has 
determined  how  the  various  salts  commonly  found  underground 
respond  to  changing  temperature  and  pressure,  it  is  impracti- 
cable to  specify  the  ores  the  precipitation  of  which  are  strongly 
favored  by  decrease  of  temperature  and  pressure.  One  would 
expect  that  precipitation  as  a  consequence  of  changing  tem- 
perature and  pressure  would  tend  to  give  a  somewhat  orderly 
vertical  distribution  of  the  various  metalliferous  ores. 

Precipitation  by  Mingling  of  Solutions. 

Precipitation  in  the  trunk-channels  is  produced  by  reactions 
caused  by  the  mingling  of  various  solutions.  The  solutions  may 
be  those  of  solids  in  the  water,  or  of  gases  in  the  water,  or  of 
both.  According  to  the  modern  theory  of  solutions,  a  solid 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       341 

dissolved  in  water  is  in  the  form  of  a  gas ;  and  therefore,  so  far 
as  the  precipitation  is  concerned,  it  makes  no  difference  whether 
the  substance  in  the  water,  if  separated,  would  be  a  solid  or  a  gas. 

It  is  evident  that  solutions  from  different  sources  are  enter- 
ing a  given  trunk-channel  at  many  places.  Each  of  the  in- 
coming streams  will  have  a  solution  different  from  that  entering 
by  any  other  stream,  although  in  many  cases  the  differences  may 
be  slight.  As  a  case  of  certain  considerable  differences  may 
be  mentioned  the  ascending  and  descending  streams.  (See  pp. 
877-378.)  Thus  a  multitude  of  streams  of  different  composi- 
tion enter  and  mingle  in  a  trunk-channel.  If  in  a  chemical 
laboratory  a  multitude  of  solutions  taken  at  random  are  thrown 
together,  it  is  certain  that  various  precipitates  will  be  formed. 
It  is  just  as  certain  when  the  various  solutions  in  an  under- 
ground channel  come  together  that  precipitates  will  frequently 
form.  This  mingling  of  solutions  is  one  of  the  most  impor- 
tant of  all  the  factors  which  results  in  the  deposition  of  the 
ores.  I  have  little  question  that  in  this  fact  of  the  wide  variety 
of  solutions  which  enters  a  given  channel  we  have  in  a  large 
measure  the  explanation  of  the  variable  richness  in  ore-de- 
posits in  a  given  fissure.  It  is  well  known  that  an  ore-deposit 
varies  in  richness  in  an  exceedingly  irregular  manner.  At  a 
place  in  a  fissure  where  a  metal  is  abundantly  found,  the  ex- 
planation in  many  cases  is  certainly  that  at  or  near  that  place 
there  entered  a  stream  which  either  carried  the  precipitated 
metal  or  carried  an  agent  capable  of  precipitating  the  metal 
which  was  already  in  the  trunk-channel.  For  instance,  it  is 
believed  that  where  the  great  bonanza  of  the  Comstock  lode 
was  found,  there  or  near  there  entered  either  solutions  rich  in 
gold  and  silver  which  met  other  solutions  capable  of  precipitat- 
ing this  gold  and  silver,  or  else  at  that  place  there  entered  a 
solution  having  a  compound  which  was  capable  of  precipitating 
the  gold  and  silver  already  traveling  upward  within  the  lode. 
Perhaps  the  former  hypothesis  is  the  more  probable. 

Ore-chutes,  or  chimneys  of  ore  of  exceptional  richness,  are 
very  frequent  phenomena  in  veins.  These  are  sometimes 
parallel  with  the  dip,  at  other  times  pitch  to  the  right  or  left 
of  it.  The  explanation  of  these  ore-chutes  in  many  instances 
I  believe  to  be  a  cross-fracture  or  joint  through  which  waters 
entered,  either  carrying  metalliferous  material  itself  or  solutions 


342       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

capable  of  precipitating  the  metalliferous  mineral  in  the  trunk- 
channel  at  the  place  where  the  lateral  streams  of  water  entered. 

The  lead  and  zinc  deposits  of  the  Mississippi  valley,  accord- 
ing to  Jenney,  are  larger  at  the  crossings  of  two  sets  of  fissures 
than  elsewhere.  This  may  be  partly  explained  by  the  greater 
abundance  of  the  solutions  furnished  by  two  sets  of  fissures, 
but  are  probably  at  least  partly  explained,  as  suggested  by 
Jenney,*  by  the  mingling  of  two  different  kinds  of  waters,  thus 
giving  conditions  favorable  for  precipitation. 

In  the  Enterprise  mine,  at  Rico,  Col.,  described  byRickard,f 
the  ore-bodies  are  in  vertical  veins  and  in  flats  under  shales. 
While  a  set  of  cross-veins  is  barren,  "  the  rich  ore-bodies  overlie 
them  in  the  contact  zone."  Below  the  shale  it  is  common  to 
find  ores  of  more  than  average  grade  in  the  pay  veins  where 
they  are  broken  by  the  cross-veins.  It  is  believed  the  explana- 
tion of  these  relations  is  the  reactions  resulting  from  the  mingling 
of  the  solutions  of  the  "  verticals  "  with  the  inclined  cross-veins. 

The  silver-lead  deposits  of  the  Aspen  district  of  Colorado, 
described  by  Spurr,  J  furnish  an  instance  of  very  probable  pre- 
cipitation of  rich  ore-chutes  by  the  mingling  of  solutions. 
Spurr  states  that  generally  an  ore-body  is  "  found  at.  the  inter- 
section of  two  faults,  one  of  these  faults  usually  dipping 
steeply,  while  the  other  is  much  flatter."  For  this  "the 
explanation  is  offered  that  by  the  mingling  of  solutions  which 
had  previously  flowed  along  different  channels  the  precipitation 
of  metallic  sulphides  was  brought  about." 

Probably  the  rich  ore-chutes  of  gold  ore  in  the  Sierra  Nevada, 
which,  according  to  Lindgren,  pitch  to  the  left  as  one  looks 
down  the  veins,  further  illustrate  the  principle  of  precipitation 
by  mingled  solutions.  For  the  most  part,  Lindgren  makes  no 
statement  as  to  the  relations  of  ore-chutes  and  lateral  seams. 
However,  on  the  Canada  Hill  vein  there  are  "  occasional  rich 
bunches  at  the  intersections"  of  the  two  systems  of  veins. § 

*  "  The  Lead  and  Zinc  Deposits  of  the  Mississippi  Valley,"  by  W.  P.  Jenney, 
Trans.,  xxii.,  1894,  pp.  189-190,  224. 

f  "The  Enterprise  Mine,  Rico,  Col.,"  by  T.  A.  Rickard,  Trans.,  vol.  xxvi., 
1897,  pp.  977-978. 

J  "Geology  of  the  Aspen  Mining  District,  Colorado,"  by  J.  E.  Spurr,  Mon. 
U.  S.  Geol  Survey,  No.  31,  1893,  pp.  230,  234-235. 

\  "  The  Gold-quartz  Veins  of  Nevada  Cityand  Grass  Valley,  California,"  by 
Waldemar  Lindgren,  17th  Ann.  Eept.  U.  S.  Geol.  Surv  ,  pt.  ii.,  1896,  p.  195. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       343 

It  is  believed  that  the  Cripple  Creek  deposits  likewise  illus- 
trate this  principle.  Penrose*  notes  that  many  of  the  rich  ore- 
chutes  occur  at  cross-fissures.  The  formation  of  these  ore- 
chutes  at  such  places  is  doubtless  partly  explained  by  the 
greater  amount  of  solutions  furnished  at  an  intersection  of  two 
trunk-lines  of  underground  circulation ;  but  it  is  thought  prob- 
able that  the  main  cause  for  the  formation  of  ore-chutes  at 
such  places  is  the  reaction  of  solutions  furnished  by  one  set  of 
fissures  upon  those  furnished  by  the  other  set.  However,  it  is 
but  fair  to  say  that  Penrose  makes  the  explanation  the 
"  mechanical  one,  in  deflecting  the  course  of  the  ore-bearing 
solutions." 

While  apparent  irregularities  in  the  kinds  and  percentages  of 
metals  are  doubtless  in  many  cases  explained  as  above,  the  dis- 
tribution of  the  metals  in  a  definite  order  from  the  surface 
downward,  and  the  general  law  that  many  valuable  metallifer- 
ous ores  grow  poorer  in  depth  if  the  measure  be  1000  meters 
or  more  are  to  be  explained  by  other  principles.  Of  these, 
varying  temperature  and  pressure  are  important;  but  more 
important  in  many  instances,  as  will  be  shown  subsequently, 
is  a  second  concentration  produced  by  descending  waters. 

Reactions  Due  to  Wall-Rocks. 

Precipitation  of  metalliferous  ores  from  the  solutions  in  the 
trunk-channels  due  to  the  influence  of  the  wall-rocks  are  fre- 
quently produced  in  the  following  ways :  (1)  It  has  already 
been  explained  that  a  solid  when  placed  in  contact  with  a  liquid 
may  precipitate  some  compound  previously  held  in  solution,  some 
part  of  the  solid  going  into  solution  at  the  same  time.  Thus,  the 
wall-rock  may  precipitate  ores.  (2)  The  wall-rock  produces  an 
effect  upon  the  trunk-solutions  by  furnishing  precipitating  solu- 
tions to  it,  and  this  may  result  in  precipitation  of  metals  already 
in  solution  within  the  trunk-channels.  (3)  The  wall-rock  itself 
may  furnish  metalliferous  material  for  the  ore-deposit  which 
may  be  precipitated  when  it  reaches  the  trunk-channel  by  the 
solutions  there  contained.  This  has  been  greatly  emphasized, 
probably  over-emphasized,  by  Sandberger.  Where  the  wall- 
rock  is  easily  soluble,  ready  enlargements  of  the  openings  occur, 

*  "Mining  Geology  of  Cripple  Creek,  Colorado,"  by  R  A.  F.  Penrose,  Jr., 
IQth  Ann.  Rept.  U.  S.  Geol.  Surv.,  1894-95,  pt.  ii.,  pp.  164-165,  1895. 


344       SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

furnishing  places  for  the  deposition  of  the  metalliferous  mate- 
rial. (See  pp.  413-416.) 

It  is  believed  that  the  effect  of  the  wall-rock  in  these  various 
ways  in  the  production  of  many  ore-deposits  is  of  great  im- 
portance. As  an  illustration,  may  be  cited  the  very  general 
association  of  lead-ores  with  limestone.  Probably  by  far  the 
larger  portion  of  the  lead-ores  mined  in  the  past  have  come 
from  within  limestone.  I  believe  it  to  be  highly  probable  that 
the  position  of  the  ores  in  limestone  is  due  to  the  character  of 
this  rock.  Any  one  of  the  factors  above  mentioned  might  be 
more  important  in  a  given  case,  but  doubtless  in  many  in- 
stances two  or  more  work  together.  Thus,  the  position  of 
the  lead  in  a  limestone  may  be  partly  explained  by  reactions 
between  the  solutions  of  the  trunk-channel  entering  the  lime- 
stone and  the  limestone  itself.  Or,  the  precipitation  of  the 
lead  may  be  partly  the  result  of  the  reactions  between  the 
solutions  furnished  by  the  trunk-channel  and  the  solutions  fur- 
nished by  the  limestone.  In  a  given  case  the  waters  of  a  trunk- 
channel  entering  the  limestone  may  be  acid.  The  solutions 
from  the  limestone  would  immediately  react  upon  this  solution, 
tending  to  neutralize  it,  and  the  precipitation  of  lead  sulphide 
might  be  a  consequence.  Or,  the  wall-rock  might  furnish  the 
lead,  as  in  the  Mississippi  valley.  The  ready  solubility  of  the 
limestone  would  furnish  the  openings  and  caves,  giving  a  re- 
ceptacle for  the  lead,  as  in  southwestern  Wisconsin. 

A  still  clearer  case  of  precipitation  resulting  from  the  influ- 
ence of  the  wall-rock  is  the  well-known  occurrence  of  metallic 
copper  about  grains  of  magnetite,  and  in  the  openings  of  sand- 
stones, conglomerates  and  amygdaloid  of  Keweenaw  Point.* 
"Where  the  copper  is  about  the  magnetite  it  seems  perfectly  clear 
that  the  protoxide  of  iron  in  the  magnetite  was  the  reducing  agent 
which  precipitated  the  metallic  copper,  f  The  metallic  copper 
between  the  particles  was  doubtless  precipitated  by  ferrous 
solutions  furnished  by  the  wall-rocks,  which  in  many  cases  are 
basic  volcanics. 

The  reactions  due  to  the  country-rock  are  more  likely  to  be 
effective  in  proportion  as  it  is  porous,  and  therefore  allows  solu- 

*  tl  The  Copper-Bearing  Kocks  of  Lake  Superior,"  by  K.  D.  Irving,  Mon.  U.  S. 
Oeol.  Surv.,  No.  5,  1883,  p.  420. 
f  Irving,  cit.,  PI.  xvi..  Fig.  1. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       345 

tions  to  permeate  it.  The  country-rock  is  especially  effective 
in  its  reactions  where  the  trunk-channel  is  a  complex  one,  and 
gives  a  large  surface  of  action.  This  is  illustrated  by  the  Calu- 
met and  Hecla  conglomerate,  by  the  Cripple  Creek  ore-de- 
posits,* and  by  many  other  districts  (see  p.  395). 

A  particularly  clear  illustration  of  the  effect  of  the  wall-rock 
is  furnished  by  ores  in  which  the  sulphides  are  confined  to  strata 
containing  organic  matter,  as  in  some  copper-depositsf  and  some 
of  the  gold-reefs  of  Australia.  In  the  case  of  the  copper-de- 
posits, the  organic  matter  has  in  all  probability  reduced  sul- 
phites or  sulphates  to  sulphides.  The  function  of  the  organic 
material  in  the  case  of  the  gold  may  have  been  to  reduce  it  to 
metallic  gold,  or  to  reduce  it  through  the  production  of  ous 
salts,  for  instance,  ferrous  sulphate  (see  pp.  373-375). 

General. 

In  conclusion,  it  may  be  said  that  the  precipitation  of  metal- 
lic ores  by  the  mingling  of  various  solutions  is  probably  the 
most  important  single  factor  which  results  in  the  first  concen- 
tration of  ores.  Probably  next  in  importance  to  this  are  the  re- 
actions upon  the  trunk-streams  due  to  the  wall-rocks.  Inas- 
much as  the  waters  of  lateral  streams  from  beyond  the 
wall-rocks  must  pass  through  the  latter,  many  of  the  streams  con- 
tributing through  the  wall-rocks  to  the  trunk-channels  produce 
an  effect  partly  due  to  materials  more  remote  than  the  wall- 
rocks  and  partly  to  the  wall-rocks.  Thus  in  many  cases  the 
effect  of  solutions  beyond  the  wall-rocks  and  that  of  solutions 
furnished  by  the  wall-rocks  cannot  be  discriminated.  How- 
ever, since  the  effect  of  the  wall-rocks  has  been  so  much  dis- 
cussed, it  seemed  to  me  best  to  treat  the  two  separately  as  far 
as  practicable. 

Diminishing  temperature  and  diminishing  pressure,  while 
probably  subordinate  in  their  effect  to  the  mingling  of  streams 
and  reactions  due  to  the  wall-rocks,  are  in  many  instances  un- 
doubtedly important,  and  in  some  instances  may  be  the  domi- 
nant factors.  In  general,  the  tendency  of  writers  has  been  to 

*  " Mining  Geology  of  Cripple  Creek,  Colorado,"  by  K.  A.  F.  Penrose,  Jr., 
16th  Ann.  Rept.  U.  S.  Geol.  Sum.,  1894-95,  pt.  ii.,  p.  163,  1895. 

f  "  The  Genesis  of  Ore-Deposits,"  by  F.  Posepny,  and  Discussion  of  same,  by 
F.  M.  F.  Cazin,  this  volume,  pp.  131,  209-210. 


346      SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

emphasize  the  effect  of  diminishing  temperature  and  pressure, 
and  to  minimize  or  even  disregard  altogether  the  effects  of 
mingling  solutions  or  the  wall-rocks,  or  both. 

The  Compounds  Deposited  by  Ascending  Waters. 

Of  the  metalliferous  ores,  those  of  iron,  copper,  lead,  zinc, 
silver  and  gold  are  the  more  important.  Where  these  are 
deposited  by  ascending  waters  they  occur  mainly  as  sulphides. 
In  many  cases  the  sulphides  are  simple  binary  salts.  However, 
sulpharsenites  and  sulpharsenates,  sulphantimonites  and  sul- 
phantimonates  are  common;  but  these  also  are  sulphides,  and  all 
will  be  thus  referred  to  without  qualification.  Besides  sulphides, 
metallic  products  sometimes  occur,  as  in  the  case  of  copper  and 
silver ;  also  tellurides,  carbonates  and  silicates  are  formed. 

"Why  average  compounds  deposited  by  ascending  waters  are, 
"for  the  most  part,  not  oxidized  compounds,  but  sulphides, 
tellurides,  or  metallic  compounds,  is  easily  explained.  The 
widely  disseminated,  downward-moving  water,  bearing  oxygen, 
is  robbed  of  this  constituent  early  in  its  course.  Ferrous  com- 
pounds are  abundantly  present  in  the  rocks  in  the  forms  of 
magnetite  and  silicates.  Iron  is  a  strong  base ;  and  where  fer- 
rous compounds  are  present  they  continue  to  abstract  the  oxy- 
gen of  the  downward  moving  waters  until  it  has  practically  dis- 
appeared. Moreover,  buried  organic  matter  takes  oxygen  from 
underground  waters.  In  believing  that  the  sulphides  are  com- 
monly precipitated  by  ascending  waters  in  the  openings  below 
the  level  at  which  oxidizing  solutions  are  active,  I  follow  Le 
Conte  and  Posepny.* 

Source  of  the  Metals. — The  nature  of  the  rocks  which  contribute 
the  metallic  salts  has  been  much  discussed.  "With  Sandberger,f 
I  have  little  doubt  that  the  metallic  constituents  of  ores  are  in 
large  part  derived  from  the  igneous  rocks  which  have  been 
intruded  or  extruded  into  the  lithosphere;  and  especially  is 
this  true  of  the  basic  rocks.  Le  Conte {  points  out  that  the  un- 
doubted frequent  occurrence  of  workable  ore-deposits  in  regions 
of  vulcanism  may  be  explained  by  the  heat  furnished  by  the 

*.  "On  the  Genesis  of  Metalliferous  Veins,"  by  Joseph  Le  Conte.  Am.  Journ. 
Sci.,  third  series,  vol.  xxvi.,  1883,  p.  4.  "The  Genesis  of  Ore-Deposits,"  by  F. 
Posepny,  this  volume  p.  44. 

f  "  Untersuchungen  fiber  Erzgange,"  by  F.  Sandberger,  1882. 

J  Op.  ciL,  p.  10. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       347 

igneous  rocks,  this  promoting  the  work  of  underground  solu- 
tions. That  the  heat  furnished  by  the  igneous  rocks  is  a  very 
important  factor  in  the  production  of  the  ore-deposits,  I  have  no 
doubt.  Since  it  is  very  difficult  to  prove  that  the  metallic  con- 
tent of  an  igneous  rock  is  original,  it  is  impossible  to  make  any 
general  statement  as  to  whether  the  metallic  content  or  the 
heat  furnished  by  the  igneous  rocks  is  the  more  important  in 
the  production  of  ore-deposits.  It  seems  to  me  clear  that  both 
are  important ;  and  equally  clear,  in  many  cases,  that  both  work 
together.  That  is  to  say,  an  igneous  rock  may  furnish  all  or  a 
part  of  the  metal  which  appears  in  an  ore-deposit,  and  the  heat 
of  the  same  igneous  rock  may  greatly  assist  its  concentration 
by  the  underground  waters. 

"While  the  massive  igneous  rocks  are  the  undoubted  source  of 
a  large  portion  of  metallic  deposits,  it  is  also  equally  certain 
that  another  large  part  is  derived  from  the  sedimentary  rocks 
and  the  metamorphosed,  or  partly  metamorphosed,  igneous  and 
sedimentary  rocks.  Lastly,  it  is  also  certain  that  many  ore- 
deposits  derive  their  metalliferous  content  in  part  from  igneous 
rocks  and  in  part  from  sedimentary  rocks.  Probably  this  is  the 
most  frequent  of  all  cases.  To  give  any  estimate  of  the  relative 
amounts  of  metalliferous  materials  derived  from  the  original 
igneous  rocks  and  from  the  secondary  rocks  is  quite1  impossible. 

This  statement  will,  of  course,  be  very  unsatisfactory  when 
applied  to  an  individual  district.  However,  it  is  not  the  pur- 
pose of  this  general  paper  to  consider  individual  districts,  ex- 
cept as  they  illustrate  principles.  It  is  properly  the  part  of  the 
geologist  or  mining  engineer  who  studies  an  individual  district 
to  find  the  source  of  the  metal.  In  many  cases,  careful  inves- 
tigations can  undoubtedly  determine  this  point,  as,  for  instance, 
that  of  the  iron-ores  of  the  Lake  Superior  region.  In  other 
districts,  however,  the  most  exhaustive  study  may  not  enable 
the  investigator  to  determine  the  source  of  the  metalliferous 
material.  This  is  especially  likely  to  be  true  of  ore-deposits 
produced  by  ascending  waters  from  a  somewhat  deep  circula- 
tion. .  The  underground  waters  may  have  their  sources  of  sup- 
ply in  rocks  which  do  not  reach  the  surface,  and  have  not 
been  penetrated  by  the  mine  workings. 

In  concluding  this  part  of  the  subject,  it  may  be  suggested 
that  in  many  instances  mistakes  have  been  made  in  assuming 


348      SOME    PRINCIPLES    CONTROLLING-   DEPOSITION    OF    ORES. 

that  some  one  formation,  sedimentary  or  igneous,  is  the  sole 
source  of  the  valuable  metals.  Such  an  assumption  is  particu- 
larly prevalent  in  papers  descriptive  of  gold  deposits  and  silver 
deposits.  In  many  districts  where  there  are  various  sedimen- 
tary and  igneous  rocks,  I  have  no  doubt  that  the  silver  and  gold 
are  partly  derived  from  two  or  several  formations. 

Source  of  the  Sulphur  of  Sulphides. — According  to  modern 
research,  the  metallic  sulphides  are  original  constituents  of 
igneous  rocks.  This  is  a  direct  observation ;  but  even  if  the 
observation  had  not  been  made,  the  large  amount  of  sulphur 
compounds  issuing  from  the  interior  of  the  earth  in  connection 
with  vulcanism  would  lead  to  the  conclusion  that  sulphides  must 
exist  in  the  igneous  rocks.  It  is  therefore  probable  that  sul- 
phur, as  sulphide,  is  or  was  present  in  sufficient  quantity  in  the 
original  rocks  to  fully  account  for  all  of  the  sulphur  compounds 
in  the  ore-deposits. 

It  is,  of  course,  well  known  that  sulphides  in  the  belt  of 
weathering  are  largely  oxidized  to  sulphites  and  to  sulphates, 
and  taken  into  solution  by  descending  waters.  These  com- 
pounds join  the  sea  of  underground  water.  There  the  sulphites 
and  sulphates,  either  just  below  the  level  of  groundwater  or  at  a 
greater  depth,  may  come  in  contact  with  buried  organic  mate- 
rial. Under  these  conditions  it  is  well  known  that  the  sulphites 
and  sulphates  are  reduced  to  ous  salts,  or  to  sulphides. 

Occasionally  the  metals  may  be  carried  to  the  trunk-channels 
as  sulphites  and  sulphates,  and  there  be  reduced  to  sulphides. 
This  would  be  especially  likely  to  happen  where  the  ores  are 
disseminated  through  beds  bearing  carbonaceous  material. 
Cazin  mentions  the  Vermont  copper-mine  as  a  case  where  the 
ores  are  mingled  with  organic  material.*  Bickard  mentions  a 
number  of  cases  where  the  deposition  of  the  ores  is  confined 
to  material  containing  organic  matter,  the  more  important 
being  those  gold-bearing  sulphide  reefs  of  Australasia,  Cali- 
fornia and  Colorado,  where  the  ore  is  associated  with  strata 
bearing  organic  matter,  f 

*  "Discussion  of  the  Genesis  of  Ore-Deposits,"  bj  M.  F.  Cazin,  this  volume, 
pp.  209-210. 

f  "The  Origin  of  the  Gold-Bearing  Quartz  of  Bendigo  Keefs,"  T.  A.  Kickard, 
Trans.,  xxii.,  1893,  314-315.  "The  Enterprise  Mine,  Rico,  Colo.,"  T.  A.  Rick- 
ard,  Trans.,  xxvi.,  1897,  977-979. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       349 

In  one  case  of  the  gold-quartz  veins  of  California,  in  carbo- 
naceous argillite,  pyrite  occurs  in  the  argillite  but  not  in  the 
quartz.  This  is  very  strongly  suggestive  that  the  carbonaceous 
matter  of  the  argillite  has  reduced  the  sulphates  to  sulphides. 
This  occurrence  in  the  California  gold-belt  is  especially  sug- 
gestive, since  the  analyses  of  two  springs  of  ascending  waters 
at  the  400-foot  levels  in  two  separate  mines  show  the  presence 
of  considerable  quantities  of  sulphates.* 

Probably  also  sulphites  and  sulphates  may  be  reduced  to 
sulphide  by  ferrous  iron  in  the  rocks.  If  this  reaction  takes 
place,  it  should  be  especially  characteristic  of  the  more  basic 
rocks.  The  frequent  occurrence  of  sulphides  in  the  altered 
basic  rocks,  and  especially  the  scoriaceous  basic  rocks,  is  very 
strongly  suggestive  that  this  reduction  has  taken  place.  So  far 
as  I  know,  this  reaction  has  not  been  before  suggested.  It  is 
probably  an  important  one  in  the  reduction  of  the  sulphites 
and  sulphates  to  sulphides  in  the  lower  part  of  the  zone  of  frac- 
ture, and  may  explain  the  deposition  of  sulphides  in  rocks  where 
organic  material  is  not  available  for  the  reduction. 

The  sulphides,  whether  as  original  constituents  of  the  igne- 
ous rocks  or  produced  by  the  above  reactions,  are  taken  into 
solution  and  deposited  in  the  main  channels  of  water-circula- 
tion. Of  the  fact  of  the  solution  and  deposition  of  the  sul- 
phides there  can  be  no  doubt.  However,  the  solvents  in  differ- 
ent cases  are  doubtless  different,  and  moreover,  in  a  single  case, 
the  solvents  are  probably  complex.  It  is  well  known  that  the 
sulphides  of  the  valuable  metals  are  somewhat  freely  soluble 
in  alkaline  solutions,  and  especially  solutions  of  the  alkaline 
sulphides. f  Furthermore,  from  observation  in  the  field  it  is 
known  that  certain  of  the  sulphides  have  been  thus  transported, 
as  for  instance  at  Steamboat  Springs  and  Sulphur  Bank,J  and 
doubtless  this  manner  of  transportation  is  very  common.  How- 
ever, as  shown  in  another  place,  the  bicarbonates  with  an  ex- 
cess of  carbon-dioxide  are  the  most  abundant  compounds  in 
underground  solutions.  These  bicarbonates  are  largely  those 

*  "The  Gold-Quartz  Veins  of  Nevada  City  and  Grass  Valley,  California,"  by 
Waldemar  Lindgren,  17^  Ann.  Eept.  U.  S.  Geol.  Surv.,  pt.  ii.,  1895-96,  p.  81 ; 
also  Plate  VIII,  p.  140,  and  pp.  121-123,  172-173. 

f  Lindgren,  op.  cit.,  pp.  177-178. 

|  Le  Conte,  cit.,  Am.  Jour.  Sci.,  Third  Series,  vol.  xxvi.,  p.  3. 


350       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

of  the  alkalies  and  alkaline  earths.  Such  carbonated  waters  also 
favor  the  solution  of  sulphides.  Furthermore,  sulphides  are 
doubtless  rendered  more  soluble  by  the  presence  of  various 
other  compounds  in  the  underground  solutions.  However,  the 
transportation  of  sulphides  is  not  limited  to  solutions  which  bear 
other  compounds ;  for  the  sulphides  themselves  are  soluble  in 
pure  water  to  some  extent,  as  has  been  shown  by  Doelter.* 

But  in  whatever  form  the  sulphides  are  transported,  they  are 
largely  precipitated  in  due  time  in  the  trunk-channels.  By  denu- 
dation these  sulphides  may  again  reach  the  belt  of  weathering 
when  the  cycle  is  complete.  The  sulphide  may  be  again  oxi- 
dized to  sulphate,  and  so  on.  It  is  therefore  clear  that  sul- 
phur, as  sulphide  and  sulphate,  may  again  and  again  take  part 
in  the  deposition  of  ores;f  but  the  first  source  of  the  sulphur 
must  be  the  sulphides  of  the  original  rocks. 

In  this  connection  Chamberlin  has  noted  that  in  Wisconsin 
waters  comparatively  near  the  surface  bear  oxygen  and  oxidized 
compounds,  while  deep  artesian  waters  are  "  marked  by  slightly 
sulphuretted  waters."  J  Thus  analyses  of  waters  in  a  region  of 
comparatively  undisturbed  sedimentary  rocks  confirm  the  state- 
ments of  the  previous  paragraphs.  That  is  to  say,  waters  which 
are  deep-seated,  and  therefore  must  take  an  upward  journey  to 
reach  the  surface,  are  likely  to  bear  sulphides. 

While  it  is  believed  that  sulphides  are  generally  deposited  by 
upward-moving  waters,  this  is  not  supposed  to  be  the  universal 
case.  Nature's  processes  are  always  too  complex  to  be  covered 
by  a  single  general  statement.  As  a  result  of  mingling  solutions 
at  various  places,  and  of  reactions  between  solutions  and  walls, 
many  lateral  moving  and  downward  moving  streams  doubtless 
do  deposit  rather  than  dissolve  sulphides.  Indeed,  in  the  fre- 
quent case  already  noted,  where  in  downward-moving  waters, 
sulphites  or  sulphates  are  reduced  by  organic  matter  to  sul- 
phides, precipitation  of  a  portion  of  the  sulphide  is  usual.  But 
still  the  statement  would  hold  true  that  upon  the  average  more 
sulphides  are  dissolved  by  descending  waters  than  deposited,  and 
more  sulphides  are  deposited  by  ascending  waters  than  dissolved. 

*  Lindgren,  op.  cit.,  pp.  179-180. 

f  Le  Conte,  op.  cit,  p.  13.     Compare  Posepny,  this  volume,  p.  72. 
J  "  The  Ore-Deposits  of  Southwestern  Wisconsin,"  by  T.  C.  Chamberlin,  Geol. 
Wis.,  vol.  iv.,  1882,  p.  547. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       351 

"We  conclude,  therefore,  that,  whatever  the  source  of  the  sulphides 
as  first  concentrates,  these  ores  are  generally  deposited  by  ascending 
waters  in  the  trunk-channels. 

Source  of  the  Carbonic  Acid  of  Carbonates. — Aside  from  sulph- 
hydric  acid,  the  other  acid  of  great  importance  in  the  deposi- 
tion of  ore-deposits  is  carbonic  acid.  This  as  is  well  known 
is,  indeed,  the  dominant  acid  contained  in  issuing  underground 
waters.  This  point  both  Le  Conte  and  Posepny  strongly  em- 
phasize.* I  have  already  pointed  out  two  sources  for  the 
excess  of  carbon-dioxide  held  in  the  underground  waters. 
"Where  vegetation  is  abundant,  carbon-dioxide  is  concentrated 
in  the  soil.  A  large  part  of  this  is  retained  in  the  belt  of  weather- 
ing by  the  process  of  carbonation  of  the  silicates,  but  another 
part  joins  the  sea  of  underground  waters.  Another  source  for 
the  carbon-dioxide  is  that  liberated  from  cavities  within  rocks. 
It  is  well  known  that  in  many  rocks  a  large  amount  of  carbon- 
dioxide  is  included  in  innumerable  microscopic  cavities.  When 
such  rocks  are  complexly  deformed  in  the  zone  of  fracture,  the 
fractures  must  intersect  many  of  these  cavities,  and  thus  liberate 
the  carbon-dioxide.  Where  there  are  zones  of  crushing,  that 
is,  where  there  are  trunk-channels  for  percolating  waters,  the 
amount  of  carbon-dioxide  which  may  thus  be  liberated  may  be 
considerable.  Another  source  for  the  carbon-dioxide  is  a  pro- 
cess of  silication,  explained  p.  332,  as  a  result  of  which  the 
carbonates  are  decomposed  by  the  silicic  acid  at  depth,  liberat- 
ing the  carbon-dioxide.  Therefore,  deep-seated  waters  are  ever 
receiving  contributions  of  carbon-dioxide,  arid  thus  are  con- 
tinually more  capable  of  taking  metals  in  solution,  until  the 
waters  reach  conditions  where  silication  does  not  occur. 

In  this  process  of  silication  alone  is  believed  to  be  an  adequate 
source  of  carbon-dioxide  ;  so  that  metals  may  be  carried  as  bicar- 
bonatesand  the  water  also  hold  a  further  excess  of  carbon-dioxide. 

A  very  interesting  confirmation  of  the  liberation  of  silica  by 
the  process  of  carbonation  near  the  surface  and  the  liberation 
of  carbon-dioxide,  probably  by  the  process  of  silication  at  depth, 
as  above  explained,  is  furnished  by  the  Geyser  mine  of  Ouster 
county,  Colorado,  described  by  Emmons.f  Here  waters  were 

*  Le  Conte,  op.  cit,  p.  11.     Posepny,  this  volume,  p.  44. 

t  "  The  Mines  of  Custer  County,  Colorado,"  by  8.  F.  Emmons,  17 'th  Ann.  Eept. 
U.  S.  Geol.  Surv.,  pt.  ii.,  1895-96,  pp.  460-464. 


352       SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

analyzed  from  the  154  meter  and  the  615  meter  levels.  The 
superficial  waters  contained  ten  times  as  much  silica  as  the 
deep-seated  waters.  In  the  deep  waters  the  carbonic  acid  is 
greatly  in  excess  of  that  contained  in  the  vadose  circulation. 

General. 

The  foregoing  statement  explains  to  some  extent  the  source 
of  the  compounds  deposited  by  ascending  waters.  But  it  is 
not  the  intention  here  to  discuss  its  application  to  each  in- 
dividual metal.  This  I  do  not  attempt,  because  I  lack  the 
necessary  accurate  observations  upon  which  such  a  discus- 
sion should  be  based.  To  tell  in  what  manner  each  of  the 
individual  metals  is  carried  will  require  very  detailed  investi- 
gation. For  instance,  the  questions  as  to  the  condition  in  which 
gold  occurs  in  the  original  rocks,  the  manner  in  which  it  is 
carried  in  solution,  and  the  form  in  which  it  is  deposited  have 
been  much  discussed.  However,  the  difficulties  in  this  and 
other  cases,  since  the  modern  theories  of  physical  chemistry 
have  been  developed,  do  not  seem  to  be  so  great  as  when  it 
was  supposed  that  we  must  regard  each  metal  in  solution  as 
combined  with  some  one  acid.  It  has  already  been  stated  that 
all  substances  are  soluble  in  water,  and  somewhat  readily  solu- 
ble in  various  underground  solutions.  It  is  believed  that  in  the 
very  dilute  underground  solutions,  metallic  salts  are  largely  in 
the  form  of  free  ions.  Therefore,  in  one  sense,  gold  and  other 
metals  in  solution  are  not  combined  with  acid  ions,  although 
they  are  balanced  by  them.  Where  precipitated,  a  metal  might 
be  thrown  down  in  the  metallic  state,  as,  for  instance,  copper, 
silver  or  gold,  by  the  ions  which  once  balanced  it  being  balanced 
by  other  metals. 

While  it  is  not  the  purpose  here  to  take  up  the  solution  and 
deposition  of  the  compounds  which  occur  in  ore-deposits  in  de- 
tail, it  is  necessary  to  refer  to  the  law  of  mass-action  in  this 
connection.  Other  things  being  equal,  those  compounds  which 
are  abundant  will  be  dissolved  in  larger  degree  during  the 
downward  course  of  the  waters,  and  the  same  compounds  will 
be  most  abundantly  precipitated  in  the  trunk-channels.  It  is 
well  known  that  iron  is  the  most  abundant  of  all  the  metallic 
compounds  in  the  crust  of  the  earth..  In  this  fact,  combined 
with  the  law  of  mass-action,  we  have  the  dominating  abundance 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       353 

of  iron  sulphide  as  compared  with  all  sulphides  of  other 
metals.  It  is  well  known  in  many  cases  that  the  deeper  a 
mine  goes  below  the  level  of  groundwater,  the  greater  the 
proportion  of  iron  sulphide  and  the  less  the  proportion  of 
the  other  metals,  as  a  result  of  which,  combined  with  increased 
cost  of  working,  it  frequently  does  not  pay  to  work  a  deposit 
beyond  a  certain  depth.  The  law  of  mass-action  explains  the 
abundance  of  the  iron  sulphide ;  it  does  not  explain  the  fre- 
quent relative  increase  in  the  iron  sulphide  and  the  decrease  of 
more  valuable  sulphides  as  one  passes  from  the  level  of  ground- 
water  into  deep  workings.  To  explain  this  we  must  take  into 
account  the  effect  of  the  downward-moving  waters,  discussed 
under  the  succeeding  heading. 

We  have  now  seen  that  the  zone  of  fracture  is  searched  by 
the  percolating  waters ;  that  metalliferous  materials  taken  into 
solution  by  the  downward  and  lateral  moving  waters  are  carried 
to  the  trunk  channels  of  underground  circulation ;  that  in  these 
trunk  channels  the  metalliferous  materials  are  precipitated  in 
various  ways.  Thus  a  first  concentration,  by  ascending  waters 
giving  sulphurets  and  metals  of  some  of  the  elements,  is  fully 
accounted  for. 

In  some  cases  the  deposits  thus  produced  are  sufficiently  rich, 
so  that  they  are  of  economic  importance.  In  these  cases,  which 
undoubtedly  exist,  but  which  perhaps  are  less  numerous  than 
one  might  at  first  think,  a  concentration  by  ascending  waters 
has  been  sufficient. 

A  conspicuous  illustration  of  ore-deposits  of  this  class  which 
may  be  mentioned  are  the  metallic  copper  deposits  of  the  Lake 
Superior  region.  The  copper  was  in  all  probability  reduced 
and  precipitated  directly  as  metallic  copper  from  upward  mov- 
ing cupriferous  solutions.  The  reducing  agents  were  the  fer- 
rous compounds  in  the  solid  form,  in  part  as  magnetite  and  as 
solutions  derived  from  the  iron-bearing  silicates.  When  the 
copper  was  precipitated,  the  iron  was  changed  into  the  ferric 
condition.*  It  is  well  known  that  metallic  copper  once  formed 
is  but  slowly  affected  by  the  oxidizing  action.  Oxidation  has, 
in  fact,  occurred  in  the  Lake  Superior  region,  but  from  the 

*  "  Paragenesis  and  Derivation  of  Copper  and  its  Associates  on  Lake  Superior," 
by  E.  Pumpelly,  Am.  Jour.  ScL,  Third  Series,  vol.  ii.,  1871,  p.  353. 


354      SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OP    ORES. 

facts  now  to  be  observed  not  to  an  important  extent.  An  oxi- 
dized belt  may  have  formed  in  pre-glacial  times,  but  if  so  it 
was  swept  away  by  glacial  erosion,  and  sufficient  time  has  not 
since  elapsed  to  form  another.  The  ore-deposits  now  worked 
have  apparently  remained  practically  unchanged  since  the  time 
of  their  first  concentration.  In  this  fact  we  have  the  explana- 
tion of  the  great  richness  of  these  deposits  to  extraordinary 
depths. 

As  a  case  of  sulphide  deposits  which  continue  to  great  depth 
without  diminution  in  richness,  may  be  mentioned  the  gold- 
quartz  veins  of  Nevada  City  and  Grass  Valley,  California. 
According  to  Lindgren,  "  it  can  be  confidently  stated  that 
there  is  no  gradual  diminution  of  the  tenor  of  the  ore  in  the 
pay-chutes  below  the  zone  of  surface  decomposition,"*  although 
within  the  same  chute  there  are  many  and  great  variations  in 
richness.  This  statement  is  applicable  to  deposits  which  reach 
a  vertical  depth  of  500  or  600  meters.  If  Lindgren  is  correct 
in  thinking  the  gold-quartz  veins  of  the  Sierra  Nevada  do  not 
diminish  in  depth  below  an  extremely  superficial  upper  zone, 
this  would  be  a  case  in  which  sulphuret  ores  were  sufficiently 
concentrated  by  ascending  waters  alone  to  afford  workable  ore- 
deposits. 

THE  PRECIPITATION  OF  ORES  BY  ASCENDING  AND  DESCENDING 
WATERS  COMBINED. 

Thus  far  we  have  considered  ores  precipitated  by  ascending 
waters  alone.  However,  many  of  the  ores  thus  produced  have 
been  profoundly  modified  by  the  action  of  descending  waters. 

"Where  the  point  of  exit  of  the  ascending  waters  of  the  trunk 
channels  is  in  a  valley  or  near  the  level  of  surface  drainage, 
the  waters  may  continue  to  ascend  quite  to  the  surface.  How- 
ever, where  the  openings  are  below  slopes  the  waters  ordinarily 
do  not  continue  to  ascend  to  the  surface,  but  make  their  way 
laterally  from  the  trunk-channel  at  and  below  the  level  of 
groundwater  (see  Fig.  6).  Above  the  level  of  groundwater, 
and  frequently  for  a  certain  distance  below  the  level  of  ground- 
water,  the  movement  is  downward  in  the  openings.  The  water 

*  "  The  Gold-Quartz  Veins  of  Nevada  City  and  Grass  Valley,  California,"  by 
Waldemar  Lindgren,  llth  Ann.  Rept.  U.  S.  Geol  Surv.,  pt.  ii.,  1895-96,  p.  163. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       355 

thus  moving  downward  includes  not  only  that  which  directly 
passes  into  the  trunk  openings  at  the  surface,  but  a  much 
larger  quantity  which  converges  into  these  openings  from  the 
smaller  openings  on  all  sides. 

In  regions  in  which  mining  is  going  on,  denudation  has  ordi- 
narily truncated  the  veins  for  considerable  depths,  in  many 
cases  to  hundreds  or  even  thousands  of  meters.  It  is  therefore 
clear,  in  a  majority  of  cases,  that  portions  of  the  fissures  in 
which  the  waters  are  now  descending  were,  in  the  past,  in  all 
probability  much  deeper  below  the  surface,  and  therefore  the 
waters  at  that  time  in  the  larger  fissures  were  probably  ascend- 
ing. During  the  time  the  water  was  ascending,  the  first  con- 
centration of  sulphurets  and  other  products  took  place.  But 
as  a  result  of  the  downward  migration  of  the  belt  of  weather- 
ing and  the  downward  movement  of  water  in  that  belt,  altera- 
tion and  secondary  concentration  of  ore-deposits  have  taken 
place.  This  second  concentration  of  ore-deposits  is  of  the  very 
greatest  importance,  and  I  believe  largely  explains  the  frequent 
greater  richness  of  the  upper  50  or  100  or  500  meters,  and  in 
some  cases  1000  meters,  as  compared  with  lower  levels. 

It  has  already  been  pointed  out  that  the  descending  waters 
bear  oxygen  and  carbon  dioxide ;  and  furthermore,  that  solu- 
tion is  taking  place.  Moreover,  the  belt  of  weathering  is  mi- 
grating downward  because  of  erosion.  The  result  of  all  these 
changes  is  to  produce  an  upper  belt  of  second  concentrates  from 
the  first  concentrates  formed  by  ascending  waters.  This  material 
may  be  divided  into  three  parts  :  (1)  above  the  level  of  ground- 
water  is  a  belt  largely  composed  of  oxides,  carbonates,  chlorides 
and  associated  products,  which,  however,  may  contain  enriched 
sulphides.  (2)  Above  and  below  the  level  of  groundwater  is 
a  transition  belt  composed  of  sulphides  rich  in  the  valuable 
metals,  such  as  gold,  silver,  copper,  lead  and  zinc,  which,  how- 
ever, contain  subordinate  amounts  of  oxidized  products.  (3) 
Deeper  down  is  a  belt  of  lean  sulphides  bearing  small  amounts 
of  the  more  valuable  sulphurets,  and  which  commonly  passes 
into  iron  sulphide.  Between  the  three  classes  of  material  there 
are  gradations.  The  oxidized  belt  gradually  passes  into  the 
rich  sulphide  belt;  the  rich  sulphide  belt  gradually  passes  into 
the  poor  sulphide  belt. 

The  above  results  are  due  to  a  complicated  set  of  reactions 

23 


356       SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

which  cannot  here  be  given  in  full.  It  is,  however,  clear  that 
if  the  sulphides  are  equally  abundant  the  sulphide  which  is  the 
most  easily  oxidized  will  be  the  first  to  disappear.  The  order 
of  disappearance  will  therefore  be  iron,  copper,  zinc,  lead,  silver. 
It  is,  however,  understood  that  the  oxidation  of  an  easily  de- 
stroyed sulphide  is  not  complete  before  the  oxidation  of  a  re- 
fractory sulphide  has  begun.  All  of  the  sulphides  are  oxidized 
all  the  time,  but  the  more  readily  a  sulphide  is  oxidized,  the 
more  rapidly  it  is  destroyed.  During  oxidation  the  sulphides 
are  largely  altered  to  soluble  sulphates,  which  are  taken  into 
solution  and  carried  downward. 

The  evidence  of  the  extensive  formation  of  sulphates  in  veins 
by  descending  water  is  found  in  the  presence  of  sulphates  in 
mine  waters  and  in  the  frequent  formation  and  precipitation 
of  basic  ferric  sulphate  in  the  veins,  as,  for  instance,  at  Cripple 
Creek,*  and  in  the  Mercur  district,  Utah.t  The  formation  of 
gypsum  and  magnesium  sulphate  in  veins  is  scarcely  less  posi- 
tive evidence  of  the  oxidation  of  the  sulphides  to  sulphates. 
Further  evidence  of  the  formation  of  sulphates  by  oxidation  of 
the  sulphides  is  furnished  by  the  hydrous  sulphate  of  aluminum 
which  occurs  in  the  gold-veins  of  California.  J 

The  sulphides,  however,  are  not  all  oxidized  to  sulphates ;  a 
portion  of  them,  by  oxidation,  break  up  into  sulphurous  oxide 
and  oxides  of  the  metals.  A  part  of  the  oxides  unite  with  the 
carbonic  acid  to  produce  carbonates.  Finally  the  oxides  and 
oxidized  salts,  both  formed  in  place  and  transported,  react  upon 
the  unaltered  sulphides,  producing  richer  sulphurets.  The 
reactions  may  be  between  an  oxide  or  a  salt  of  a  metal  and  its 
sulphide,  as,  for  instance,  the  oxide  or  sulphate  of  copper  upon 
the  sulphide  of  copper,  as  given  by  the  following  equations : 

6CuS  +  2Cu20  =  5Cu2S  +  S02, 
and 

6CuS  +  2Cu2S04  +  3H2O  =  5Cu2S  +  2H2S04  +  H2S03. 


*  "Mining  Geology  of  the  Cripple  Creek  District,"  by  B.  A.  F.  Penrose,  Jr., 
16^  Ann.  RepL  U.  S.  Geol.  Surv.,  pt.  ii.,  1894-95,  p.  130. 

f  "Economic  Geology  of  the  Mercur  Mining  District,  Utah,"  by  J.  Edw. 
Spurr,  16th  Ann.  Rept.  U.  S.  Geol.  &u,rv.,  pt.  ii.,  1894-95,  p.  433. 

J  "The  Gold-Quartz  Veins  of  Nevada  City  and  Grass  Valley,  California,"  by 
Waldemar  Lindgren,  17^  Ann.  Rept.  U.  S.  Geol.  Surv.,  pt.  ii.,  1895-96,  p.  120. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       357 

Or  the  reaction  may  be  between  the  oxide  or  salt  of  one  metal 
and  the  sulphide  of  another  metal,  as,  for  instance,  copper  oxide 
or  copper  sulphate  upon  iron  sulphide,  thus  precipitating  cop- 
per sulphide.  The  particular  reactions  in  an  individual  case 
will  depend  upon  the  relative  solubilities  of  the  compounds 
present,  and  the  law  of  mass-action.  This  will  more  clearly 
appear  upon  subsequent  pages. 

The  concentrations  by  ascending  and  descending  waters  have 
been  considered  as  if  they  were  successive.  In  some  instances 
this  may  be  the  case ;  but  frequently  it  is  much  more  probable 
that  ascending  and  descending  waters  are  at  work  upon  the 
same  fissure  at  the  same  time,  and  that  their  products  are,  to  a 
certain  extent,  simultaneously  deposited.  For  instance,  under 
the  conditions  represented  by  Fig.  6,  a  first  concentration  by 
ascending  waters  is  taking  place  in  the  lower  part  of  the  fissure, 
and  a  second  concentration  by  descending  waters  is  taking  place 
in  the  upper  part  of  the  fissure.  Between  the  two  there  is  a 
belt  in  which  both  ascending  and  descending  waters  are  at 
work.  The  rich  upper  part  of  an  ore-deposit  which  is  worked 
in  an  individual  case  may  now  be  in  the  place  where  ascending 
waters  alone  were  first  acting,  where  later,  as  a  consequence  of 
denudation,  both  ascending  and  descending  waters  were  at  work, 
and  still  later,  where  descending  waters  alone  are  at  work.  The 
more  accurate  statement  for  this  class  of  ore-deposits,  therefore, 
is  that  ascending  waters  are  likely  to  be  the  potent  factor  in  an 
early  stage  of  the  process,  that  both  may  work  together  at  an 
intermediate  stage,  and  that  descending  waters  are  likely  to  be 
the  potent  factor  in  the  closing  stage  of  the  process. 

The  above  general  statement  may  perhaps  be  better  under- 
stood if  supplemented  by  a  consideration  of  specific  associa- 
tions of  the  metals.  The  associations  which  are  chosen  for 
illustrative  purposes  are  as  follows :  (1)  associations  of  lead, 
zinc  and  iron,  (2)  associations  of  copper  and  iron,  (3)  associa- 
tions of  silver  and  gold  with  the  base  metals. 

THE  ASSOCIATION  OF  LEAD,  ZINC  AND  IRON  COMPOUNDS. 

In  order  to  understand  the  relations  of  the  lead,  zinc  and 
iron  compounds  where  they  occur  together  in  ore-deposits,  it 
seems  advisable  to  take  an  individual  district  rather  than  to 
make  a  general  statement.  An  excellent  illustration  of  the 


358      SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

association  of  these  metals  is  furnished  by  the  Upper  Missis- 
sippi Valley,  and  this  district  will  therefore  be  considered. 

Facts  of  Occurrence. 

Here,  as  is  well  known,  in  openings  in  limestones,  lead  and 
zinc  minerals  are  associated  with  marcasite,  and  some  pyrite  and 
chalcopyrite.*  Calcite  is  an  abundant  gangue  mineral,  as  would 
be  expected,  but  it  and  the  other  gangue  minerals  will  here 
not  be  taken  into  account.  Since  the  pyrite  and  chalcopyrite 
are  very  subordinate,  they  will  not  again  be  alluded  to.  All  of 
the  sulphide  of  iron  will  be  referred  to  as  marcasite. 

The  order  of  occurrence  in  the  district  is  commonly  as  fol- 
lows :  Above  the  level  of  groundwater  in  the  belt  of  weather- 
ing the  dominant  valuable  minerals  are  galena  and  smithsonite. 
Frequently  encrusting  the  galena,  or  in  crystals  upon  it,  there 
are  some  cerussite  and  less  anglesite;  with  the  smithsonite 
there  is  some  sphalerite.  The  smithsonite  may  extend  5  or 
10  meters  below  the  level  of  groundwater;  but  deeper  the 
oxidized  products  almost  wholly  disappear.  The  smithsonite 
below  the  level  of  groundwater  is  explained  in  some  cases  by 
the  material  being  along  a  main  channel  of  downward  percolat- 
ing waters ;  in  other  cases  by  the  fact  that  the  level  of  ground- 
water  is  probably  now  higher  than  it  once  was,  as  a  result  of 
depression  and  valley-filling  at  the  close  of  the  glacial  epoch; 
thirdly,  by  the  well-known  general  downward  movement  of 
oxidizing  water  somewhat  below  the  level  of  groundwater; 
and,  fourthly,  by  reactions  between  oxidized  lead  salts  and  the 
sphalerite.  (See  p.  361.)  Below  the  galena  and  smithsonite 
is  sphalerite,  with  a  large  amount  of  marcasite.f  For  much 
of  the  district  the  workings  have  not  extended  far  below  the 
level  of  groundwater,  but  in  certain  parts  of  the  district  work- 
ing has  extended  for  a  considerable  depth. 

While  the  above  general  statement  is  correct  for  much  of 
the  district,  it  must  be  understood  that  a  single  sulphide  does 

*  "  The  Ore-Deposits  of  Southwestern  Wisconsin,"  by  T.  C.  Chamberlin,  Geol. 
of  Wis.,  vol.  iv.,  1882,  pp.  380-393. 

f  Chamberlin  emphasizes  the  inferior  position  of  the  zinc  as  compared  with 
the  lead  and  the  association  of  the  zinc  and  iron,  but  he  does  not  consider  the  posi- 
tions of  these  compounds  with  reference  to  the  level  of  groundwater.  LOG.  cit.,  pp. 
488-491. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.    -  359 

not  occur  at  a  given  level  to  the  exclusion  of  the  others.  In- 
deed, in  many  cases  all  of  the  sulphides  are  found  at  the  same 
level.  In  many  of  the  smaller  veins  the  sulphides  occur  in  a 
definite  order.  The  full  succession  at  various  openings,  from 
the  wall  to  the  druse,  is  (1)  marcasite,  (2)  ferriferous  sphalerite, 
(3)  galena,  in  cubic  crystals,  (4)  ferriferous  sphalerite  (subordi- 
nate in  quantity),  (5)  marcasite,  (6)  galena,  in  octahedral  crystals 
(very  subordinate  in  quantity).*  Of  this  succession  at  various 
veins  some  of  these  elements  are  lacking.  A  very  common 
order  is  (1)  sphalerite,  (2)  galena,  and  (3)  marcasite. 

First  Concentration. 

No  clearer  possible  illustration  could  be  found  of  the  general 
principles  of  ore  deposition  by  the  underground  waters,  and  the 
phenomenon  of  crustification  emphasized  by  Posepny,  than  that 
furnished  by  this  district.  The  first  concentration  is  believed  to 
be  the  work  of  ascending  waters,  the  materials  being  precipi- 
tated in  the  form  of  sulphides.  It  is  probable  that  there  was  a 
tendency  at  the  time  of  the  original  crystallization  for  the  sul- 
phides to  be  thrown  down  in  a  definite  order  across  the  open- 
ings, as  shown  by  the  phenomena  of  crustification.  Further- 
more, it  appears  that  there  may  have  been  two  main  cycles  of 
precipitation,  so  far  at  least  as  the  sphalerite  and  galena  are 
concerned,  but  the  first  cycle  was  by  far  the  more  important. 
It  is  also  possible  that  there  was  a  tendency  for  the  sulphides 
to  be  precipitated  in  a  definite  order  vertically,  as  a  consequence 
of  which  the  marcasite  was  the  predominate  precipitate  at  the 
lowest  level,  sphalerite  at  the  intermediate  levels,  and  galena 
at  higher  levels.  Such  an  order  might  be  explained  as  a  result 
of  the  lessening  pressure  and  temperature  as  the  depositing 
solutions  rose  in  the  openings. 

Second   Concentration. 

While  it  is  possible  that  the  vertical  order  of  the  minerals  is 
due  to  a  first  concentration,  it  is  probable  that  this  is  not  the 
most  important  factor  in  the  regular  vertical  distribution  of  the 
sphalerite  and  galena.  It  is  believed  that  the  present  general 
order  of  these  materials  is  mainly  controlled  by  the  downward- 
moving  waters  combined  with  denudation. 

*  Chamberlin,  loc.  tit.,  pp.  491-497. 


360       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

It  is  not  necessary  to  show  that  the  smithsonite  above  and  a 
short  distance  below  the  level  of  groundwater  was  largely  de- 
rived from  sphalerite,  and  that  the  cerussite  and  anglesite  were 
largely  derived  from  galena.  The  details  of  the  relations  of  the 
various  oxidized  and  sulphuretted  minerals  above  the  level  of 
groundwater  are  exceedingly  complex,  and  no  description  of 
them  will  here  be  attempted.  NOT  in  this  paper  is  it  necessary 
to  write  reactions  for  the  transformation  of  the  sulphides  into 
the  oxidized  products,  since  the  general  characters  of  such  re- 
actions are  so  well  known.*  It  is,  however,  necessary  to  ex- 
plain how  downward-percolating  waters  may  concentrate  galena 
at  a  high  level  and  sphalerite  at  a  lower  level. 

Galena. — If  it  be  premised  that  the  ascending  waters  evenly 
distributed  the  sulphides,  at  least  so  far  as  the  vertical  element 
is  concerned,  it  is  certain  that  downward-moving  waters,  com- 
bined with  denudation,  may  concentrate  the  galena  at  high 
levels  and  the  sphalerite  at  lower  levels. 

The  galena  is  the  most  difficultly  oxidizable  of  the  three  sul- 
phides. It  is,  therefore,  the  most  stable  of  them.  By  the  oxida- 
tion and  solution  of  the  sphalerite  and  marcasite  above  the  level 
of  groundwater  the  galena  would  be  concentrated.  That  this 
process  has  taken  place  on  an  extensive  scale  is  shown  by  the 
occurrence  of  many  detached  fallen  crystals  and  masses  of 
galena  in  the  openings  above  the  level  of  groundwater,  and 
also  at  the  bottoms  of  the  wider  openings  and  caves  a  short 
distance  below  the  level  of  groundwater.  Indeed,  a  considerable 
portion  of  the  lead  of  the  district  which  has  been  taken  above 
or  within  a  few  feet  below  the  level  of  groundwater  strongly 
corroborates  the  idea  of  concentration  as  result  of  solution  of 
the  other  sulphides  which  held  the  galena  to  the  walls,  thus  per- 
mitting the  material  to  drop  to  lower  positions  in  the  ere  vices,  f 

While  the  concentration  of  the  galena  is  partly  explained  as 
above,  it  may  be  explained  also  in  part  by  chemical  reactions 
between  the  various  compounds.  In  the  belt  of  weathering 
part  of  the  galena  as  already  noted  is  being  oxidized,  as  is 
shown  by  the  incrustations  and  superimposed  crystals  of  cerus- 
site and  anglesite.  During  the  formation  of  the  sulphates  and 


Chamberlin,  loc.  cit. ,  pp.  497-509. 
Chamberlin,  loc.  cit.,  pp.  453  to  497. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       361 

carbonates,  a  certain  amount  of  these  salts  is  taken  into  solution 
and  carried  downward.  These  sulphates  and  carbonates  would 
react  upon  the  other  sulphides  present  and  reprecipitate  the 
lead  as  galena.'  These  reactions  might  take  place  to  some 
extent  above,  but  would  be  especially  likely  to  occur  below, 
the  level  of  groundwater.  As  a  result  of  the  downward  migra- 
tion of  the  belt  of  weathering,  there  would  be  in  the  down- 
ward-moving waters  a  continual  supply  of  the  sulphates  and 
carbonates  of  lead.  The  chief  reaction  would  be  that  between 
the  lead  salts  and  the  dominant  iron  sulphide.  Supposing  the 
iron  were  in  the  form  of  FeS,  the  reactions  may  be  written  as 
follows : 

PbS04  +  FeS  =  PbS  +  FeS04, 

PbC03  +  FeS  =  PbS  +  FeC03. 

If  the  iron  be  supposed  to  be  in  the  form  of  FeS2,  as  is  most 
likely,  oxygen  also  would  be  necessary  for  the  reactions.  The 
equations  would  then  be  as  follows : 

PbS04  -f  FeS2  +  02  =  PbS  +  FeS04  +  S02, 
PbC03  +  FeS,  +  02  =  PbS  +  FeC03  +  S02. 

However,  it  has  been  premised  that  with  the  original  sul- 
phides zinc  sulphide  is  present,  and  this  may  also  react  upon 
the  lead  salts,  according  to  the  following  reactions  : 

PbS04  +  ZnS  =  PbS  +  ZnS04, 
PbC03  +  ZnS  =  PbS  +  ZnC03. 

In  the  case  of  the  latter  reaction,  smithsonite  would  be 
formed.  In  this  connection  it  is  notable  that  frequently  asso- 
ciated with  the  galena  for  some  distance  below  the  level  of 
groundwater,  smithsonite  occurs,  as  already  noted.  While  a 
part  of  the  smithsonite  below  the  level  of  groundwater  is  of  this 
origin,  doubtless  the  larger  portions  of  it  are  differently  ex- 
plained. (See  p.  358.) 

To  the  foregoing  reactions,  partly  explaining  the  concentra- 
tion of  galena,  objection  may  be  made  upon  account  of  the 
small  solubility  of  lead  sulphate  and  lead  carbonate.  It  is  true 
that  these  substances  are  very  sparingly  soluble  in  pure  water; 
however,  they  are  sufficiently  soluble  in  waters  bearing  carbon- 
dioxide  to  account  for  the  phenomenon.  If  this  be  not  the 
case,  the  lead  may  have  been  carried  downward  as  chloride. 


362      SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

Independent,  however,  of  chemical  theory,  we  know  in  many 
districts,  and  particularly  in  the  lead  and  zinc  district  of  south- 
western Wisconsin,  that  the  galena  has  been  changed  to  some 
soluble  form  upon  an  extensive  scale.  As  evidence  for  this  in- 
ference, galena  crystals  above  the  level  of  groundwater  are 
much  corroded,  and  the  amount  of  cerussite  and  anglesite  asso- 
ciated with  them  is  so  small  as  not  to  account  for  the  corrosion, 
and  therefore  the  lead  has  been  transformed  to  a  soluble  salt, 
which  has  been  transported  below  in  important  amounts.*  So 
far  as  my  argument  is  concerned,  it  is  of  no  consequence 
whether  the  lead  is  as  a  sulphate,  carbonate,  chloride  or  other 
salt.  However,  it  is  believed  that  these  are  the  forms  in  which 
the  lead  was  transferred  on  the  most  extensive  scale.  I  regard 
the  cerussite  and  anglesite  as  evidence  of  the  partial  transfer  of 
the  lead  as  sulphate  and  carbonate.  A  large  amount  of  sul- 
phate and  carbonate  probably  formed,  but  the  compounds  are 
so  insoluble  that  a  part  of  the  salts  produced  were  not  carried 
downward,  but  precipitated  near  the  places  of  formation. 

Sphalerite. — Zinc  holds  sulphur  less  strongly  than  lead,  but 
much  more  strongly  than  iron.  Therefore,  the  sphalerite  would 
be  concentrated  in  the  zone  below  the  galena,  the  reactions 
being  similar  to  those  producing  the  galena.  They  may  be 
written  as  follows : 

ZnS04  -f  FeS  =  ZnS  +  FeS04, 
ZnCO,  +  FeS  =  ZnS  +  FeCO?, 

ZnS04  -f  FeS,  -f  02  =  ZnS  +  FeS04  +  S02, 
ZnC03  +  FeS2  +  O2  =  ZnS  +  FeC03  +  S02. 

Marcasite. — At  a  certain  depth  in  the  openings  below  the 
level  of  groundwater,  nearly  all  of  the  salts  of  lead  and  zinc 
descending  from  the  belt  of  weathering  would  be  precipitated 
by  reactions  between  them  and  the  iron  sulphide,  as  above 
explained.  The  remainder  of  this  paragraph  cannot  be  said  to 
apply  to  the  deposits  of  the  upper  Mississippi  Valley ;  for  the 
vertical  extent  of  the  veins  is  probably  very  limited,  many  of 
them  apparently  being  cut  off  by  impervious  strata  within  short 
distances  from  the  surface.  However,  in  veins  in  which  the 

*  Chamberlin,  op.  cit.,  pp.  498-499,  500. 


or 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       363 

first  concentration  extends  to  a  depth  greater  than  that  to  which 
downward-moving  waters  are  effective,  only  the  sulphurets  of 
the  first  concentration  would  be  found  below  this  level.  These 
sulphurets  would  consist  mainly  of  marcasite,  with  subordinate 
amounts  of  sphalerite  and  galena.  However,  even  in  this  belt, 
concentration  of  galena  and  sphalerite  may  occur  to  some  ex- 
tent, although  it  receives  no  contribution  from  the  lead  and  zinc 
salts  from  above ;  for  even  after  the  salts  of  lead  and  zinc  travel- 
ing downward  from  the  belt  of  weathering  are  all  precipitated, 
the  waters  may  still  hold  oxygen.  This  oxygen  would,  to  the 
largest  extent,  act  upon  the  marcasite,  producing  to  some  extent 
soluble  salts  which  would  be  abstracted,  and  thus  reduce  the 
quantity  of  this  material,  and  relatively  enrich  the  deposits  in 
lead  and  zinc,  although  not  increasing  the  absolute  amount  of 
lead  and  zinc  present  in  a  given  vertical  distance.  So  far  as  the 
zinc  and  lead  salts  were  oxidized  by  the  oxygen-bearing  water, 
these  would  react  upon  the  iron  sulphide  again,  and  they  would 
be  precipitated  according  to  the  reactions  above  given. 

General. 

It  is  believed  that  the  concentration  by  descending  waters 
explains,  through  the  reactions  given  on  pp.  106-107,  the  orderly 
distribution  of  the  ores  in  a  vertical  direction,*  although  orig- 
inal deposition  by  ascending  waters  may  have  produced  its  ef- 
fect. Furthermore,  it  is  believed  that  this  concentration  was 
the  final  determinative  factor  in  making  the  ores  so  rich  as  to 
warrant  exploitation.  This  statement  in  reference  to  the  rich 
deposits  applies  both  to  the  oxidized  products  and  to  the  sul- 
phurets, both  above  and  below  the  level  of  groundwater.  This 
process  of  concentration  is  primarily  chemical,  but  also  to  some 
extent  is  mechanical,  the  latter  being  especially  true  of  the  ga- 
lena loosened  by  solution  from  the  walls  which  have  fallen  to 
the  lower  positions  in  the  crevices  and  caves. 

While  the  reactions  of  the  downward  moving  oxidized  prod- 
ucts upon  low  grade  sulphurets,  thus  producing  rich  sulphides, 
have  been  dwelt  upon,  it  is  not  supposed  that  these  are  the  only 
reactions  which  have  resulted  in  enrichment.  As  pointed  out 
by  Chamberlin,f  organic  matter  has  made  its  way  into  the 

*  Compare  Chamberlin,  op.  cit.}  pp.  551-553. 
f  Chamberlin,  op.  cit.,  p.  544. 


364      SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

openings  of  the  limestone,  and  as  farther  indicated  by  Chamber- 
lin,* and  emphasized  by  Blake, f  organic  matter  is  abundant  in 
certain  of  the  shaly  layers.  As  argued  by  Chamberlin  and 
Blake,  organic  material  in  the  rocks  from  both  of  these  sources 
was  probably  an  important  factor  in  the  reduction  and  precipi- 
tation of  the  downward  moving  sulphates.  As  pointed  out  by 
Blake,  the  evidence  of  the  effect  of  this  organic  matter  is  es- 
pecially clear  in  the  cases  of  the  large  sphalerite  deposits  which 
rest  upon  the  oil-rock  at  the  top  of  the  Trenton  as  a  floor. 

My  own  views  in  reference  to  the  concentration  of  the  ores 
in  the  upper  Mississippi  valley  differ  somewhat  from  those  of 
Chamberlin, J  Whitney,  §  and  others,  who  have  held  that  these 
ores  are  products  of  descending  and  lateral-secreting  waters 
alone;  but  still  more  from  those  of  Percival||  and  Jenney,lf  who 
have  held  that  the  ores  were  derived  from  a  deep-seated  source. 
The  first  supposed  the  transportation  to  have  taken  place 
through  igneous,  the  second  through  aqueous  agencies.  Since 
the  discussion  of  this  difference  of  view  involves  the  influence 
of  some  of  the  special  factors  considered  later,  it  is  deferred  to 
pp.  397-405. 

Therefore,  so  far  as  practicable,  the  above  statement  concern- 
ing concentrations  by  ascending  and  descending  waters  and  the 
reactions  of  the  sulphates  upon  the  sulphides  is  made  without 
reference  to  the  special  features  of  the  upper  Mississippi  valley 
district.  This  procedure  has  been  followed  because  it  is  believed 
that  in  many  of  the  lead  and  zinc  districts  of  the  world  the 
above  statement  is  applicable  in  its  main  features. 

THE  ASSOCIATION  OF  COPPER  AND  IRON  COMPOUNDS. 
Another  very  general  association  of  metals  is  that  of  copper 
and  iron.     It  is  well  known,  where  this  association  occurs,  that 


*"  Chamberlin,  op.  tit.,  p.  546. 

f  "Lead  and  Zinc  Deposits  of  the  Mississippi  Valley,"  by  Wm.  P.  Blake, 
Trans.  A.  I.  M.  E.,  xxii.,  pp.  630-631.  "  Wisconsin  Lead  and  Zinc  Deposits,"  by 
Wm.  P.  Blake,  Butt.  G.  S.  A.,  vol.  v.,  1894,  pp.  28-29. 

f  Chamberlin,  op.  cit.,  pp.  544-549. 

§  Whitney,  "Geol.  of  Wis.,"  vol.  i.,  1862,  pp.  398,  et  seq. 

||  Percival,  "Ann.  Kept.  Geol.  Surv.  of  Wis.,"  1855,  pp.  30-33;  "Ann.  Kept. 
Geol.  Surv.  of  Wis.,"  1856,  p.  63. 

T[  Jenney,  "  Lead  and  Zinc  Deposits  of  the  Mississippi  Valley,"  Trans.  Am.  Inst. 
Min.  Eng.,  vol.  xxii.,  1894,  pp.  219-223. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       365 

above  the  level  of  groundwater,  cuprite  (Cu20),  tenorite  (CuO), 
azurite  (2CuC03,  Cu(OH)2)  and  malachite  (CuC03,  Cu(OH)2)  are 
very  frequently  found.  It  is  further  very  well  known  that 
below  the  level  of  groundwater  these  oxidized  and  carbonated 
products  occur  in  greatly  diminished  quantity,  and  that  rich 
sulphurets  frequently  occur,  such  as  chalcocite  (Cu2S),  bornite 
(Cu3FeS3)  and  chalcopyrite  (CuFeS2),  and  sometimes  covellite 
(CuS).  Somewhat  deeper  below  the  level  of  groundwater  the 
oxides  and  carbonates  are  not  found.  Furthermore,  the 
chalcocite,  covellite  and  bornite  are  very  generally  restricted  to 
the  upper  part  of  the  belt  of  groundwater ;  deeper,  the  places 
of  these  minerals  are  largely  occupied  by  chalcopyrite.  Not 
only  this,  but  still  deeper  the  chalcopyrite  is  less  prominent  in 
many  instances,  and  the  iron  sulphides  more  prominent.  In 
the  lower  workings  of  many  of  the  deeper  mines  the  only 
metalliferous  product  found  is  cupriferous  iron  sulphides,  the 
chalcopyrite  having  wholly  disappeared. 

Whether  or  not  this  general  statement  is  correct  for  a  par- 
ticular area,  each  mining  engineer  can  judge  from  his  own 
knowledge.  There  may  be  exceptions  to  it,  due  to  various 
causes,  one  of  which  has  been  alluded  to  in  explaining  bonan- 
zas. Thus  below  cupriferous  pyrites  there  may  again  be  found 
richer  copper  sulphides.  Indeed,  as  before  stated,  ore-deposits 
vary  greatly  in  their  richness  both  horizontally  and  vertically,* 
and  the  above  statement  can  only  be  considered  as  a  general 
average. 

The  above  order  is  believed  to  be  explained  by  the  work  of 
downward-moving  waters.  The  combinations  of  lead,  zinc 
and  iron  were  followed  from  above  downward.  The  reactions 
which  occur  in  the  case  of  the  copper-iron  deposits  we  may  per- 
haps follow,  to  vary  the  order,  from  the  base  upward.  At  greater 
or  less  depths  below  the  level  of  groundwater  the  ores  are 
frequently  cupriferous  pyrites,  the  direct  deposit  of  the  ascend- 
ing waters.  At  a  little  higher  level  oxygen  from  above  may 
have  oxidized  a  portion  of  the  iron  and  transported  it  else- 
where, thus  relatively  enriching  the  deposit  in  copper.  At  a 
still  higher  level  there  will  be  a  contribution  of  soluble  copper 
salts  from  above.  Since  copper  sulphate  would  certainly  be  the 

*  This  volume,  p.  264-265. 


366       SOME   PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

most  common  salt,  for  convenience  all  the  soluble  salts  will  be 
regarded  as  sulphates.  Reactions  similar  to  those  given  below 
may  easily  be  written  for  other  salts. 

At  the  level  where  salts  of  copper  appear  from  above,  by  the 
reaction  of  the  copper  salt  upon  iron  sulphide,  chalcopyrite 
may  be  produced,  the  reactions  following  from  the  fact  that 
copper-iron  sulphides  are  less  soluble  than  iron  sulphides,  and 
from  the  law  of  mass  action.  The  reactions  may  be  written  as 
follows : 

CuS04  +  2FeS  =  CuFeS2  +  FeS04, 
or 

CuS04  +  2FeS2  +  O4  =  CuFeS2  +  FeSO4  +  2S02. 

Where  the  iron  sulphide  is  pyrrhotite,  intermediate  between 
FeS  and  FeS2,  the  reactions  may  be  written  by  combining  the 
above  equations  in  proper  proportions. 

In  passing  upward  from  the  lowest  level  at  which  the  chal- 
copyrite appears,  this  mineral  may  steadily  increase  in  quan- 
tity until  it  becomes  an  important  constituent,  and  finally  the 
iron  sulphide  may  become  subordinate.  Under  these  circum- 
stances bornite  is  likely  also  to  appear.  The  production  of 
bornite  by  the  direct  reactions  of  the  copper  salts  upon  iron 
sulphide  may  be  supposed  to  be  as  follows : 

Cu2S04  4-  CuS04  +  3FeS  =  Cu3FeS3  +  2FeS04? 
or 

Cu2SO4  +  CuS04  +  3FeS2  +  06  =  Cu3FeS3  + 
2FeS04  +  3S02. 

However,  the  bornite  may  also  be  produced  by  the  reaction 
of  the  copper  salt  upon  the  chalcopyrite  itself.  For  instance : 

2CuFeS2  +  CuS04  +  02  =  Cu3FeS3  4-  FeS04  +  S02. 

Reactions  might  also  be  written  for  the  production  of  the 
bornite  from  the  chalcopyrite  by  the  reaction  of  cuprous 
sulphate  and  oxygen.  Further  reactions  might  be  written  as 
result  of  which  the  bornite  is  derived  from  chalcopyrite  and 
iron  sulphide  together ;  but  it  is  hardly  worth  while  to  do  this, 
since  no  new  principle  is  illustrated. 

Passing  to   still  higher  levels,  with  the    chalcopyrite    and 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       367" 

bornite  chalcocite  may  appear.  The  chalcocite  may  be  pro- 
duced directly  by  the  reaction  of  cuprous  salt  upon  iron 
sulphide,  as  follows : 

Cu2S04  +  FeS  =  Cu2S  +  FeS04, 
or 

Cu2S04  +  FeS2  +  02  =  Cu2S  +  FeS04  +  S02. 

Furthermore,  the  chalcocite  may  be  produced  by  reactions 
of  the  sulphates  either  upon  the  chalcopyrite  or  upon  the 
bornite.  In  the  first  case  the  reaction  may  be  written  as 
follows : 

CuFeS2  +  CuS04  +  02  =  Cu2S  +  FeSO,  +  SO2, 

or  from  the  bornite  by  the  following  reaction : 

Cu3FeS3  +  CuS04  +  O2  =  2Cu2S  -f  FeS04  +  S02. 

Of  course,  it  is  understood  that  these  sulphides  overlap  one 
another.  Before  the  iron  sulphide  has  wholly  been  replaced  by 
chalcopyrite,  bornite  may  appear.  At  the  place  where  bornite 
has  become  reasonably  abundant,  chalcocite  may  be  found. 
However,  certain  general  statements  may  be  made.  If  the 
dominating  material  is  iron  sulphide,  the  copper  mineral  which 
is  present  is  likely  to  be  chalcopyrite  rather  than  the  richer 
sulphurets.  Chalcopyrite,  on  the  one  hand,  is  likely  to  be 
associated  with  the  pyrites,  and  on  the  other  hand  with  bornite, 
or  even  chalcocite.  Bornite  and  chalcocite  are  likely  to  be 
associated  with  each  other  and  with  chalcopyrite,  but  with  the 
first  two  compounds  iron  sulphide  is  likely  to  be  subordinate  or 
absent. 

At  still  higher  levels  in  a  mine,  a  moderate  distance  below 
the  level  of  groundwater,  oxidized  and  carbonated  products 
may  appear  with  the  sulphurets.  These  mixed  products,  some- 
times called  oxysulphurets,  are  well  illustrated  in  the  Appa- 
lachian, Arizona  and  Montana  deposits.*  Still  higher,  and  es- 
pecially above  the  level  of  groundwater,  the  oxidized  products 
may  become  dominant,  for  there  the  rich  sulphurets  which 
have  emerged  from  the  level  of  groundwater  have  been 
directly  acted  upon  by  the  oxygen  and  carbon-dioxide.  A 

*  "The  Copper  Kesources  of  the  United  States,"  by  James  Douglas,  Trans., 
xix.,  1891,  690,  etseq. 


368      SOME    PRINCIPLES   CONTROLLING   DEPOSITION   OF    ORES. 

series  of  transformations  now  take  place  which  may  result  in 
metallic  copper,  cuprite,  tenorite,  azurite  and  malachite.  As 
in  the  case  of  the  lead  and  iron,  the  nature  of  these  reactions 
is  so  well  known  that  they  will  not  here  be  written  out.  The 
oxidation  of  the  sulphur  and  copper  may  be  simultaneous,  or 
the  sulphur  may  be  oxidized  first,  forming  metallic  copper, 
which  may  later  be  oxidized  in  whole  or  in  part.  The  oxi- 
dized products  may  be  first  the  oxide,  cuprite.  This  may 
be  altered  to  tenorite,  and  this,  later,  may  unite  with  carbon- 
dioxide  and  water  to  form  the  hydro-carbonates,  azurite,  and 
finally,  by  further  hydration,  malachite.  Illustrating  this  pro- 
cess, Prof.  Penrose  has  shown  me,  in  a  single  hand-specimen 
from  the  oxidized  belt  of  the  Arizona  mines,  concentrically 
arranged  metallic  copper,  cuprite,  tenorite,  and  carbonate  of 
copper,  the  copper  being  in  the  core  and  the  carbonate  of 
copper  on  the  outside.  The  oxidized  products  may  largely 
remain  in  place,  furnishing  rich  ores,  or  they  may  be  almost 
wholly  dissolved  and  carried  to  lower  levels,  to  react  upon  the 
sulphides,  as  already  explained. 

Therefore,  largely  by  processes  of  oxidation  and  reaction 
upon  sulphurets,  first  forming  rich  sulphurets  and  later  rich 
oxidized  products,  there  may  be  concentrated  in  the  upper  few, 
or  few  score,  or  few  hundred  meters  of  a  vein,  a  large  part  of 
the  copper  produced  by  a  first  concentration  through  a  much 
greater  distance.  Since  the  reactions  already  considered  are 
not  the  only  ones  which  enter  into  the  second  concentration  of 
rich  deposits,  individual  illustrative  cases  are  deferred  until 
after  the  other  factors  are  considered.  (See  pp.  383-389.) 

By  the  foregoing  it  is  not  meant  to  imply  that  each  copper 
sulphide  deposit  has  gone  through  the  entire  history  above 
detailed.  Indeed,  there  is  no  doubt  that  the  general  story  out- 
lined will  need  much  modification  when  applied  to  an  indi- 
vidual case.  However,  it  is  held  that  some  process  of  sec- 
ondary concentration  similar  to  that  outlined  has  been  a  very 
important  factor  in  the  production  of  rich  copper  deposits  at 
many  localities. 

THE  ASSOCIATION  OF  SILVER  AND  GOLD  WITH  THE  BASE  METALS. 

The  two  common  cases  of  the  association  of  lead,  zinc  and 

iron,  and  that  of  the  association  of  copper  and  iron,  have  now 


SOME   PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       369 

been  considered.  A  similar  set  of  transformations  can  be 
traced  out  in  either  of  these  classes  of  deposits  which  contain 
associated  silver  and  gold. 

Silver. 

In  the  case  of  silver,  it  is  well  known  that  the  original 
forms  are  generally  sulphides,  sulphantimonites,  sulphanti- 
monates,  sulpharsenites,  and  sulpharsenates.  Silver  sulphide 
is  a  compound  which  holds  strenuously  to  its  sulphur.  Ordi- 
narily it  is  not  sufficiently  abundant  to  constitute  the  main  mass 
of  an  ore-deposit.  However,  since  it  holds  so  strongly  to  its 
sulphur,  the  silver  salts  are  likely  to  be  found,  in  the  case  of 
lead-zinc-iron  compounds,  most  abundantly  with  the  lead,  less 
abundantly  with  the  zinc,  and  least  abundantly  with  the  iron ; 
and  in  the  case  of  the  copper-iron  compounds,  most  abundantly 
with  the  copper  and  less  abundantly  with  the  iron.  The  rich 
silver  compounds,  viz.,  native  silver,  cerargyrite  (AgCl),  argen- 
tite  (Ag2S),  proustite  (Ag3AsS3),  pyrargyrite  (Ag3SbS3),  steph- 
anite  (Ag5SbS3),  may  be  abundantly  found  in  the  upper  parts 
of  mines,  but  frequently  decrease  in  amount  in  passing  from 
the  surface  deep  into  the  zone  of  sulphides,  and  at  sufficient 
depth  in  this  zone  these  silver  minerals  may  entirely  disappear, 
the  products  being  wholly  argentiferous  lead,  zinc,  copper,  and 
iron  minerals.  In  many  cases  independent  silver  minerals  do 
not  occur  at  all,  all  of  the  silver  being  in  the  lead,  zinc,  copper, 
and  iron  compounds.  In  the  case  of  the  lead,  zinc,  and  iron 
deposits,  as  the  ores  become  poorer  in  lead  and  zinc,  they  are 
also  likely  to  become  poorer  in  silver.  Also,  in  case  the  cop- 
per-iron deposits  become  poorer  in  copper  with  depth,  the  silver 
will  also  ordinarily  decrease  in  amount.  Therefore  the  plumb- 
iferous  and  zinciferous  pyrites  and  cupriferous  pyrites  deep 
down  are  ordinarily  lower  in  silver  than  the  deposits  above, 
which  are  richer  in  the  base  metals. 

In  this  general  paper  it  is  hardly  worth  while  to  write  the 
reactions  for  the  production  of  the  rich  silver  sulphurets. 
Since  silver  holds  to  its  sulphur  more  strenuously  than  any  of 
the  base  metals  with  which  it  is  associated,  the  first  of  these 
baser  metals  which  is  met  in  mass  will  be  reacted  upon  by  the 
silver  salts.  Suppose,  for  instance,  that  in  the  belt  of  weather- 
ing the  silver  sulphide  is  oxidized  to  silver  sulphate  or  changed 


370      SOME   PRINCIPLES    CONTROLLING    DEPOSITION   OP    ORES. 

to  silver  chloride.  The  first  of  the  salts  and  the  second  to 
some  extent  are  taken  into  solution  and  pass  down  where  they 
may  come  in  contact  with  chalcocite.  Argentite  would  then 
he  precipitated  according  to  the  following  reactions : 

Cu2S  +  Ag2SO,  =  Ag2S  +  Cu2S04. 
Cu2S  +  2AgCl  =  Ag2S  +  2CuCl. 

In  a  manner  similar  to  the  treatment  of  the  other  salts,  vari- 
ous other  reactions  could  he  written  between  salts  of  silver  and 
the  other  sulphides  of  copper,  lead,  zinc  and  iron.  For  the 
present  purposes,  it  is  only  necessary  to  understand  that  the 
silver  will  he  concentrated  either  as  an  independent  silver  sul- 
phuret  or  as  a  silver  sulphide  associated  with  the  rich  sulphides 
of  the  base  metals. 

As  a  case  in  which  silver  is  concentrated  in  a  sulphide  rather 
than  in  the  carbonate,  may  be  mentioned  the  Leadville  ores. 
Here,  according  to  Emmons,  the  galena  is  much  richer  in  silver 
than  the  cerussite.  Not  only  is  this  so  in  general,  but  there  are 
some  very  interesting  special  cases.  For  instance,  in  the  case 
of  five  assays  of  galena  nodules  which  had  carbonate  crusts, 
"  there  are  six  times  as  much  silver  in  the  galena  as  in  the  ce- 
russite."* This  discrepancy  may  be  partly  explained  by  the  ab- 
straction of  the  silver  as  sulphate  from  the  lead  carbonate,  but 
I  suspect  it  to  be  mainly  explained  by  the  reaction  of  the  oxi- 
dized silver  salts  upon  the  galena,  producing  a  galena  richer  in 
silver  than  originally  existed. 

Above  the  level  of  groundwater  the  silver  occurs  to  some  ex- 
tent in  the  native  form,  but  more  largely  as  cerargyrite.  Silver 
does  not  readily  unite  with  oxygen,  hence  the  explanation  of 
the  metallic  form.  However,  it  does  have  a  strong  affinity  for 
chlorine,  and  where  that  element  is  present  cerargyrite  is  likely 
to  be  found. 

Where  the  silver  is  largely  changed  to  the  sulphate  and 
chloride,  and  is  not  largely  precipitated  as  cerargyrite,  the  upper 
part  of  the  silver  veins  in  the  «belt  of  weathering  may  be  greatly 
depleted  in  silver  as  a  result  of  this  leaching  process.  That 
the  silver  is  not  thrown  down  as  cerargyrite  may  be  due  to  a 

*  "  Geology  and  Mining  Industry  of  Leadville,"  by  S.  F.  Emmons,  Mon.  No. 
12,  U.  S.  Geol.  Surv.,  1886,  pp.  553-554. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       371 

deficiency  of  chlorine  in  the  descending  solutions,  or  to  the  fact 
that  the  solutions  are  of  such  a  character  or  so  abundant  that 
they  are  capable  of  dissolving  the  silver  chloride.  Probably 
illustrating  this  process  of  depletion  is  the  Cripple  Creek  dis- 
trict, where  the  upper  parts  of  the  veins  which  carry  free  gold 
are  deficient  in  silver,  while  the  original  telluride  contains  a 
certain  amount  of  silver,  showing  that  the  silver  has  probably 
been  leached  out* 

Gold. 

Gold  occurs  extensively  (1)  in  the  native  form,  (2)  associated 
with  the  sulphides,  and  (3)  as  a  telluride. 

In  the  belt  of  weathering,  gold  is  very  largely  found  in  the 
metallic  form  associated  with  the  oxidized  products  of  the  base 
metals,  and  especially  with  oxide  of  iron.  Much  of  such  gold 
has  plainly  been  associated  with  sulphides  or  has  been  united 
with  tellurium. 

Below  the  level  of  groundwater  the  most  common  associa- 
tions of  gold  are  the  sulphides  of  the  base  metals.  Where 
base  metals  other  than  iron  do  not  occur,  gold  occurs  associated 
on  a  great  scale  with  pyrite.  In  such  associations,  where  the 
sulphides  are  abundant,  the  gold  is  likely  to  be  plentiful ; 
where  the  sulphides  are  deficient,  the  gold  is  also  likely  to  be 
deficient. f  This  relation  is  illustrated  both  by  California  and 
Australasia.  The  relation  suggests  that  the  original  solution 
and  deposition  of  native  gold  is  frequently  connected  with  that 
of  the  sulphides,  and  therefore  it  is  reasonable  to  infer  that  the 
same  conditions  which  produced  sulphides  also  resulted  in  the 
solution  and  precipitation  of  gold. 

In  various  districts  in  the  Cordilleran  region,  and  especially 
in  Colorado,  and  more  particularly  in  the  Cripple  Creek  dis- 
trict, the  original  form  in  which  much  of  the  gold  was  de- 
posited is  a  telluride.  J 

*  "  Mining  Geology  of  the  Cripple  Creek  District,"  by  E.  A.  F.  Penrose,  Jr., 
16th  Ann.  Rept.  U.  S.  Geol.  Surv.,  pt.  ii.,  1894-95,  pp.  131-132. 

t  "The  Gold-Quartz  Veins  of  Nevada  City  and  Grass  Valley,  California,"  by 
Waldemar  Lindgren,  17th  Ann.  Rept.  U.  S.  Geol.  Surv.,  pt.  ii.,  1895-96,  pp.  124- 
126.  "  The  Genesis  of  Certain  Auriferous  Lodes,"  by  J.  E.  Don,  Trans.,  xxvii., 
1898,  567. 

I  "Mining  Geology  of  the  Cripple  Creek  District,"  by  E.  A.  F.  Penrose,  Jr., 
IQth  Ann.  Rept.  U.  S.  Geol.  Surv.,  pt.  ii.,  1894-95,  pp.  119-121. 

24 


372      SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

The  original  form  of  the  gold  of  the  Judith  mountains*  is 
also  a  telluride.  Telluride  of  gold  further  occurs  in  the  gold- 
belt  of  California,t  in  the  mines  of  Ouster  county,  Colorado, J 
and  in  western  Australia, §  associated  with  sulphides.  Pearce 
suggests  1 1  that  the  free  gold  which  occurs  in  various  regions 
may  have  been  originally  deposited  as  a  telluride  which  was 
later  oxidized  in  the  belt  of  weathering.  The  Cripple  Creek 
district,  in  which  the  gold  in  the  weathered  zone  is  in  the 
metallic  form,lf  furnishes  an  excellent  illustration  of  the  forma- 
tion of  free  gold  from  a  telluride. 

From  the  foregoing  it  is  plain  that  gold  may  be  originally 
precipitated  by  ascending  solutions  in  a  vein  as  metallic  gold, 
as  a  telluride,  or  partly  in  both  forms.  Moreover,  either  one 
or  both  of  these  forms  may  be  associated  with  the  sulphides  of 
the  base  metals. 

Nothing  has  thus  far  been  said  as  to  the  form  in  which  the 
gold  is  transported.  However,  it  is  certain  that  gold  is  soluble 
in  the  various  underground  solutions,  and  especially  in  the 
alkaline  sulphides.  Moreover,  gold  readily  makes  combina- 
tions with  iodine  and  chlorine,  and  as  an  iodide  and  chloride 
is  easily  soluble.  Also  alkaline  iodides  are  capable  of  dissolv- 
ing gold.**  Furthermore,  gold  is  soluble  in  ferric  sulphate. 
That  gold  and  the  salts  of  gold — one  of  which  we  know  to 
exist  in  nature  as  a  solid,  the  telluride — are  soluble  in  under- 
ground solutions  is  the  main  point.  Since  the  modern  ideas 
of  physical  chemistry  have  been  developed,  the  form  in  which 
the  gold  is  carried  is  put  in  a  new  light.  It  was  supposed  that 
it  must  be  regarded  as  united  with  one  or  more  of  the  other 
ions  present.  Since  underground  solutions  of  gold  are  exceed- 
ingly dilute,  it  is  highly  probable  that  the  gold  is  ionized  or  is 

*  " Geology  and  Mineral  Resources  of  the  Judith  Mountains  of  Montana,"  by 
W.  H.  Weed  and  L.  V.  Pirsson,  18^  Ann.  Kept.  U.  S.  Geol.  Surv.,  pt.  iii., 
1896-97,  pp.  589,  591,  597. 

f  Lindgren,  op.  cit.,  p.  117. 

J  "The  Mines  of  Custer  County,  Colorado,"  by  S.  F.  Emmons,  17th  Ann. 
Eept.  U.  S.  Geol.  Surv.,  pt.  ii.,  1895-96,  p.  433. 

\  "  The  Superficial  Alteration  of  Western  Australian  Ore-Deposits,"  by  H.  C. 
Hoover,  Trans.,  xxviii.,  1899,  762. 

||  Proc.  Colo.  Sci.  Soc.,  vol.  ii.,  1885,  pp.  1-6. 

if  Penrose,  op. cit.,  p.  119-120. 

**  "  The  Origin  of  the  Gold-bearing  Quarts  of  Bendigo  Eeefs,  Australia,"  by 
T.  A.  Rickard,  Trans.,  xxii.,  1894,  pp.  308-309. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       373 

in  the  free  state.  Thus  regarded,  it  would  be  kept  in  the 
ionic  state  not  by  any  one  of  the  associated  acid  ions  present, 
but  partly  by  all  of  them.  While  the  above  is  true,  it  is  also 
doubtless  true  that  certain  solutions  are  much  more  capable  of 
dissolving  gold  and  gold  salts  than  others,  and  upon  this  point 
further  investigation  is  needed. 

In  whatever  form  gold  is  carried,  it  is  known  to  be  precipi- 
tated in  the  first  concentration  as  a  telluride,  or  as  metallic 
gold  associated  with  tellurides  or  sulphides,  or  both.  "Whether 
it  is  also  precipitated  as  a  sulphide  is  uncertain.  Too  little  is 
known  about  the  tellurium  salts  or  the  origin  of  the  tellurides 
to  enable  one  to  make  any  statement  concerning  the  precipita- 
tion of  gold  in  this  form.  However,  it  is  comparatively  easy 
to  suggest  agencies  which  may  have  resulted  in  the  precipita- 
tion of  gold  in  the  metallic  form.  When  it  is  remembered 
that  copper  is  extensively  precipitated  in  the  metallic  form  in 
the  Lake  Superior  region,  and  that  gold  is  even  more  readily 
reducible,  the  frequent  precipitation  of  gold  in  the  metallic 
form  need  occasion  no  surprise.  Gold  would  be  precipitated 
in  the  metallic  form  by  organic  matter  or  by  any  ous  salt. 

Rickard*  calls  attention  to  the  frequent  association  of 
metallic  gold  with  sedimentary  rocks  bearing  organic  matter 
in  Colorado,  California,  ISTew  Zealand,  Australia  and  Tas- 
mania, f  The  most  remarkable  case  is  the  concentration  of  gold 
in  veins  where  they  cross  strata  of  carbonaceous  shale,  called  in- 
dicators. Says  Don,{  "  Away  from  the  indicator,  the  greater 
part  of  the  vein  quartz  is  absolutely  barren ;  but  at  the  inter- 
section with  the  indicator  larger  masses  of  gold  (often  more 
than  100  ounces  in  one  piece)  have  been  obtained,  and  the 
greater  part  of  the  gold  extracted  from  this  belt  has  come 
from  those  parts  of  the  quartz  veins  near  some  one  of  the 
indicators."  Furthermore,  Bickard§  describes  experiments  in 
which  the  black  carbonaceous  shale  of  Rico  was  placed  in  silver 
solutions  and  in  solutions  containing  Cripple  Creek  gold-ore. 

*  Trans.,  xxii.,  314-315. 

f  "The  Indicator  Veins,  Ballarat,  Australia,"  by  T.  A.  Rickard,  Eng.  and 
Min.  Journ.,  vol.  lx.,  1895,  pp.  561-562. 

J  "The  Genesis  of  Certain  Auriferous  Lodes,"  by  J.  E.  Don,  Trans.,  xxvii., 
1898,  p.  569. 

%  "The  Enterprise  Mine,  Col.,"  by  T.  A.  Eickard,  Trans.,  xxvi.,  1897,  pp. 
978-979. 


374       SOME    PRINCIPLES    CONTROLLING   DEPOSITION   OF    ORES. 

Both  metallic  silver  and  gold  were  abundantly  precipitated 
upon  the  shale  in  a  short  time.  In  the  instances  above  men- 
tioned it  can  hardly  be  doubted  that  the  organic  material  was 
an  important  or  controlling  factor  in  the  reduction  and  precipi- 
tation of  the  gold. 

Gold  would  also  be  precipitated  from  solutions  which  came 
in  contact  with  ferrous  oxide,  such  as  magnetite,  or  by  solu- 
tions bearing  ferrous  or  cuprous  sulphate,  or  any  other  ferrous 
or  cuprous  salts.  When  it  is  remembered  that  ous  salts  are 
extensively  produced  underground  (see  pp.  348-349),  it  becomes 
highly  probable  that  such  solutions  are  frequently  the  cause 
of  the  precipitation  of  gold  with  sulphurets.  Since  iron  is  the 
most  abundant  of  all  the  metals  carried  in  underground  solu- 
tions, such  sulphates  would  be  more  likely  to  be  sulphates  of 
iron  than  any  other.  If  the  salts  formed  in  the  belt  of 
weathering  were  ferric  sulphates,  they  would  be  likely  to  be 
reduced  to  the  ferrous  condition  at  depth  by  the  ferrous  iron, 
which  is  especially  abundant  in  the  basic  rocks.  Indeed, 
analyses  of  mineral  waters  which  bear  sulphates  also  ordinarily 
show  ferrous  iron.*  Therefore  ascending  waters  bearing  fer- 
rous sulphate  or  other  ous  salt  might  be  brought  into  a  lode  by 
side-streams  and  there  precipitate  the  gold.  Such  side-chan- 
nels entering  through  lateral  cracks  may,  in  many  cases,  ex- 
plain the  extreme  irregularity  of  the  distribution  of  the  gold. 

Although  Lindgren  argues  to  the  contrary  in  the  Sierra 
Nevada,  f  the  suggestion  that  a  part  of  the  gold  there  has  been 
reduced  by  ferrous  sulphate  has  extreme  plausibility.  The  gold 
associated  with  the  pyrites  is  native.  In  that  district  two  analyses 
of  the  waters  of  feeding-streams  (the  only  analyses  reported) 
entering  the  lodes  at  a  depth  of  400  feet  are  given.  Both  of 
these  analyses  show  that  sulphates  and  iron  are  present.^  Ac- 
cording to  the  analyses  the  iron  is  reported  as  ferric ;  but  ap- 
parently no  precautions  were  taken,  when  the  waters  were  col- 
lected, to  prevent  the  oxidation  of  ferrous  to  ferric  iron.  Indeed, 
the  description  of  the  deposits  made  by  the  underground  springs 
renders  it  highly  probable  that  ferrous  salts  were  there  contained, 

*  "  Mineral  Waters  of  the  United  States,"  by  A.  C.  Peale,  Bull.  U.  S.  Geol. 
Surv.,  No.  32. 

f  Lindgren,  op.  cit.,  p.  181,  and  pi.  v.,  p.  134. 
J  Lindgren,  op.  cit.,  pp.  121-123. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.      375 

as  shown  by  the  precipitates  of  yellow  material,  which  is  partly 
ferric  oxide.  Moreover,  if  these  analyses  are  not  sufficient  evi- 
dence of  the  presence  of  sulphates,  the  clean  vein  quartz  itself, 
which  contains  a  large  number  of  fluid  inclusions,  contains  sul- 
phates,* showing  that  sulphate-bearing  waters  are  not  ex- 
ceptional, but  must  have  been  present  at  the  time  the  lodes 
themselves  were  formed.  Finally,  the  ore-shoots  have  great 
irregularities  in  richness,  for  which  Lindgren  offers  no  expla- 
nation. The  suggestion  above  made  that  the  gold  is  precipi- 
tated in  the  metallic  form  by  the  reducing  action  of  ferrous  sul- 
phate explains  all  of  these  facts.  The  deposits  are  rich  where 
the  side-springs  issued  from  cross-fissures  and  furnished  fer- 
rous sulphate  to  the  ascending  waters.  The  gold  is  in  the 
metallic  form  because  reduced  by  the  ferrous  sulphate. 

The  argillite  with  which  many  of  the  gold-ores  of  the  Sierra 
Nevada  are  associated  is  carbonaceous,f  and  this  carbonaceous 
material  may  have  assisted  in  the  production  of  the  ous  salts 
which  ultimately  reached  the  trunk-channels.  Indeed,  in  some 
places,  as,  for  instance,  where  the  pyrite  occurs  in  a  carbona- 
ceous argillite  but  not  in  quartz, J  the  gold  may  have  been 
directly  precipitated  by  the  carbonaceous  material.  But  since 
the  gold  in  the  Sierra  Nevada  is  mainly  deposited  in  open  fis- 
sures^ the  suggestion  of  reduction  of  the  major  portion  of  the 
gold  by  ous  salts,  and  especially  ferrous  sulphate,  is  thought  to 
be  the  more  plausible,  although,  as  already  explained,  the  for- 
mation of  the  ferrous  sulphate  may  be  due  in  part  to  carbon- 
aceous material  in  the  country-rock. 

It  can  hardly  be  doubted  that,  after  a  first  concentration  of 
gold  has  taken  place,  as  consequence  of  descending  waters  a 
second  concentration  may  take  place.  But  definite  equations 
cannot  be  written  until  it  is  determined  in  what  form  the  gold  is 
transported.  However,  if  in  the  solutions  we  do  not  know  the 
acids  against  which  the  gold  is  balanced  when  transported 
downward,  we  may  feel  sure  that,  when  such  solutions  reach 
the  sulphide  zone,  there  will  be  reactions  between  the  acid 

*  Lindgren,  op.  tit.,  pp.  130-131,  260,  261. 

f  "The  Gold-Quartz  Veins  of  Nevada  City  and  Grass  Valley,  California,"  by 
Waldemar  Lindgren,  llthAnn.  Eept.  U.  S.  Geol.  Surv.,  1895-96,  pt.  ii.,  p.  81, 1896. 
J  Lindgren,  op.  eit.,  p.  140,  pi.  viii. 
$  Lindgren,  op.  ciL,  p.  259. 


376       SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

ions  balancing  the  gold  and  the  bases  in  the  tellurides  and  sul- 
phides. As  a  consequence  of  these  reactions  metallic  gold,  and 
possibly  tellurides  and  sulphides,  will  be  precipitated  in  a  man- 
ner similar  to  that  of  the  precipitation  of  copper.  Individual 
cases  of  second  concentrations  will  be  considered  after  other 
factors  influencing  concentration  have  also  been  dealt  with. 
(See  pp.  383-389.) 

CONCENTRATION  BY  REACTION  UPON  SULPHIDES  COMPARED 
WITH  METALLURGICAL  CONCENTRATION. 

One  of  the  more  common  processes  of  metallurgy  for  the 
separation  of  gold,  silver,  copper  and  lead  from  iron  is  based 
upon  the  principle  explaining  the  second  concentration  given 
on  preceding  pages,  viz.,  that  iron  holds  sulphur  less  strongly 
than  the  other  elements  named.  The  sulphuretted  ores  are 
imperfectly  roasted,  thus  partly  oxidizing  them  to  oxides  and 
sulphates.  The  ores  are  then  smelted  in  a  furnace  with  a  flux. 
The  oxides  of  the  valuable  metals  and  the  sulphates  react  upon 
the  remaining  sulphides  of  all  the  metals,  producing  a  matte 
containing  the  sulphides  of  the  valuable  metals.  The  iron  gets 
all  or  nearly  all  of  the  oxygen ;  and  the  iron  oxide  unites  with 
the  fluxes  and  passes  into  the  slag. 

OTHER  REACTIONS  OF  DESCENDING  WATERS. 

In  the  foregoing  pages  the  second  concentration  of  metals  by 
solution,  downward  transportation  and  precipitation  by  reac- 
tions upon  the  sulphides  of  the  first  concentration  has  been 
emphasized.  However,  it  is  not  supposed  that  this  is  the  only 
process  which  may  result  in  enrichment  in  the  upper  parts  of 
vein  deposits  by  descending  waters.  The  enrichment  of  this 
belt  may  be  partly  caused  (1)  by  reactions  between  the  down- 
ward moving  waters  carrying  metallic  compounds  and  the  rocks 
with  which  they  come  in  contact,  and  (2)  by  reactions  due  to 
the  meeting  and  mingling  of  the  waters  from  above  and  the 
waters  from  below. 

(1)  The  descending  waters  carrying  metallic  material  dis- 
solved in  the  upper  part  of  the  veins  may  be  precipitated  by 
material  contained  in  the  rocks  below.  This  material  may  be 
organic  matter,  ferrous  salts,  etc.  So  far  as  precipitating  mate- 
rials are  reducing  agents,  they  are  likely  to  change  the  sul- 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       377 

phates  to  sulphides  and  precipitate  the  metals  in  that  form. 
While  sulphides  may  thus  be  precipitated  either  above  or  below 
the  level  of  groundwater,  they  are  more  likely  to  be  thrown 
down  below  the  level  of  groundwater.  Other  compounds  than 
reducing  agents  may  precipitate  the  downward  moving  salts  in 
other  forms  than  sulphides. 

(2)  In  a  trunk-channel,  where  waters  ascending  from  below 
meet  waters  descending  from  above,  there  will  probably  be  a 
considerable  belt  in  which  the  circulation  is  slow  and  irregular, 
the  main  .current  now  moving  slowly  upward  and  now  moving 
slowly  downward,  and  at  all  times  being  disturbed  by  convec- 
tional  movements.  Doubtless  this  belt  of  slow  general  move- 
ment and  convectional  circulation  would  reach  a  lower  level  at 
times  and  places  of  abundant  rainfall  than  at  other  times  and 
places,  for  under  such  circumstances  the  descending  current 
would  be  strong.  The  ascending  currents,  being  controlled  by 
the  meteoric  waters  falling  over  wider  areas,  and  subject  to 
longer  journeys  than  the  descending  currents,  would  not  so 
quickly  feel  the  effect  of  abundant  rainfall.  Later,  the  ascend- 
ing currents  might  feel  the  effect  of  the  abundant  rainfall  and 
carry  the  belt  of  upward  movement  to  a  higher  level  than 
normal.  However,  where  the  circulation  is  a  very  deep  one, 
little  variations  in  ascending  currents  result  from  irregularities 
of  rainfall. 

In  the  belt  of  meeting  ascending  and  descending  waters  (see 
Fig.  6),  convectional  mixing  of  the  solutions  due  to  difference 
in  temperature  would  be  an  important  phenomenon.  The 
waters  from  above  are  cool  and  dense,  while  those  from  below 
are  warm  and  less  dense.  The  waters  from  above  in  the  neutral 
zone  of  circulation  would  thus  tend  to  sink  downward,  while 
waters  from  below  would  tend  to  rise,  and  thus  the  waters  would 
be  mingled.  Still  further,  even  if  the  water  were  supposed  to 
be  stagnant  at  the  neutral  belt,  it  is  probable  that  by  diffusion 
the  materials  contributed  by  the  descending  waters  would  be 
mingled  with  the  materials  contributed  by  the  ascending  waters. 

Ascending  and  descending  solutions  are  sure  to  have  widely 
different  compositions,  and  an  accelerated  precipitation  of  met- 
alliferous  ores  is  a  certain  result.  As  a  specific  case  in  which 
precipitation  is  likely  to  occur,  we  may  recall  that  waters  as- 
cending from  below  contain  practically  no  free  oxygen  and  are 


378      SOME    PRINCIPLES    CONTROLLING   DEPOSITION   OF    ORES. 

often  somewhat  alkaline,  while  waters  descending  from  above 
are  usually  rich  in  oxygen  and  frequently  contain  acids,  as  at 
Sulphur  Bank,  described  by  Le  Conte.*  The  mingling  of  such 
waters  as  these  is  almost  sure  to  result  in  precipitation  of  some 
kind.  Le  Conte  further  suggestsf  that,  by  the  mingling  of 
the  waters  from  below  with  those  from  above,  the  temperature 
of  the  ascending  column  will  be  rapidly  lessened,  and  this  also 
may  result  in  precipitation,  but  the  dilution  would  work  in  the 
reverse  direction. 

The  metals  precipitated  by  the  mingling  of  waters  may  be 
contributed  by  the  descending  waters,  by  the  ascending  waters, 
or  partly  by  each.  In  so  far  as  more  than  an  average  amount 
of  metallic  material  is  precipitated  from  the  ascending  waters, 
this  would  result  in  the  relatively  greater  richness  of  the  upper 
part  of  veins  independently  of  the  material  carried  down  from 
above. 

The  above  methods  of  precipitation  and  enrichment  of  the 
upper  parts  of  deposits  follow  from  the  reactions  of  downward 
moving  waters.  Their  effect  may  be  to  precipitate  the  metals 
of  the  ascending  water  to  some  extent  and  thus  assist  in  the 
first  concentration.  But  the  results  of  these  processes  cannot 
be  discriminated  from  the  second  concentration  resulting  from 
an  actual  downward  transportation  of  the  material  of  the  first 
concentration.  It  is  believed  that  the  downward  transportation  of 
metals  is  the  most  important  of  the  causes  explaining  the  character  of 
the  upper  portions  of  lodes  (see  pp.  355—357)  ;  but  whether  this  be  so 
or  not,  their  peculiar  characters  are  certainly  due  to  the  effect  of  de- 
scending waters. 

SECOND  CONCENTRATION  FAVORED  BY  LARGE  OPENINGS  OF  THE 
BELT  OF  WEATHERING. 

The  concentration  of  large  ore-bodies  in  the  belt  of  weather- 
ing is  greatly  favored  by  the  abundance  and  size  of  the  open- 
ings as  compared  with  the  openings  existing  at  greater  depths. 

The  openness  of  the  rocks  above  the  level  of  groundwater 
and  the  comparative  lack  of  openings  below  the  level  of  ground- 
water  have  already  been  alluded  to  as  general  phenomena,  and 


*  Compare  Le  Conte,  Am.  Journ.  Sci. ,  iii. ,  vol.  xxvi. ,  p.  9. 
f  Le  Conte,  op.  cit.,  p.  12. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       379 

an  explanation  offered  for  their  existence,  viz.,  that  in  the  belt 
of  weathering,  solution  is  the  law,  and  in  the  belt  of  cementa- 
tion, deposition  is  the  law.  (See  pp.  327-329.)  Of  course,  it  is 
understood  that  there  is  usually  not  a  sudden  change  in  the 
amount  of  opening  space,  but  that  the  extremely  open  upper 
ground  grades  into  the  much  less  open  lower  ground  at  and 
below  the  level  of  groundwater.  In  some  instances  the  grada- 
tion requires  some  distance.  This  openness  of  the  belt  of 
weathering  and  the  comparative  closeness  of  the  belt  of  ce- 
mentation is  well  illustrated  by  many  limestone  regions;  for 
instance,  the  lead  and  zinc  district  of  southwestern  Wisconsin, 
already  described,  pp.  358-364,  397-405.  It  is  also  well  illus- 
trated by  the  Leadville  district  of  Colorado,  where,  Emmons 
says,  "  There  is  a  noticeable  absence,  in  the  region  of  greatest 
ore-development,  of  channels  extending  downward."*  Thus, 
so  far  as  the  openings  are  concerned,  the  conditions  for  the 
formation  of  large  ore-deposits  are  more  favorable  above  the 
level  of  groundwater,  and  as  far  below  the  level  of  groundwater 
as  openings  are  numerous,  than  at  deeper  levels. 

The  existence  of  numerous  and  large  openings  below  the 
level  of  groundwater  may  be  explained  in  individual  cases  in 
a  number  of  ways.  Of  course,  the  more  recent  the  earth- 
movements,  the  more  numerous  and  larger  are  the  openings. 
In  some  places  the  descending  waters  are  not  saturated  when 
they  reach  the  level  of  groundwater,  and  solution  continues 
for  some  distance  below  that  level.  Furthermore,  the  level 
of  groundwater  varies  under  different  circumstances.  Where 
a  region  is  being  uplifted,  the  level  of  groundwater,  other 
things  being  equal,  will  be  descending.  Where  a  region  is 
subsiding,  the  level  of  groundwater  will  be  rising.  As  a  re- 
sult of  physiographic  changes,  there  may  be  alternate  valley 
filling  and  valley  erosion.  These  changes  affect  the  level  of 
groundwater.  In  Pleistocene  time  there  was  an  extensive 
period  of  valley  filling  instead  of  erosion.  Consequent  on 
this,  the  level  of  drainage,  and  therefore  the  level  of  ground- 
water,  rose.  Also  there  may  be  very  considerable  variations 
of  the  level  of  groundwater,  as  a  consequence  of  long-con- 

*  "The  Geology  and  Mining  Industry  of  Leadville,"  by  S.  F.  Emmons,  Mon. 
U.  S.  Geol.  Surv.,  No.  12,  1886,  p.  573. 


380       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

tinued  climatic  changes ;  such,  for  instance,  as  the  alternating 
periods  of  humidity  and  aridity  in  the  Cordilleras  of  the  West 
in  connection  with  the  Pleistocene.*  The  annual  variations  in 
rainfall  cause  a  less-marked  change  in  the  position  of  the  level 
of  groundwater.  All  these  changes  favor  alternate  solution 
and  deposition;  solution  when  the  water  falls,  precipitation 
when  it  rises.  Where  the  underground  water  has  been  at  a 
low  level,  this  will  be  favorable  to  the  production  of  large 
openings.  Where,  later,  for  some  reason,  the  level  of  ground- 
water  rises,  these  openings  are  in  a  very  favorable  condition  to 
be  filled  with  ore,  as  a  result  of  the  reactions  of  the  descending 
solutions  on  the  ores  below  and  of  the  mingling  of  ascending 
and  descending  waters. 

It  might  be  argued  that  the  existence  of  ore-deposits  in  the 
large  openings  near  the  surface  is  evidence  that  the  ores  were 
not  first  deposited  by  ascending  waters.  However,  as  has  been 
already  explained,  in  the  large  openings  there  may  be  concen- 
trated mineral  material  originally  distributed  by  ascending 
waters  through  a  much  greater  vertical  distance.  Thus,  a  very 
rich  ore-deposit,  formed  by  the  reaction  of  descending  waters 
upon  a  first  concentration  produced  by  ascending  waters,  might 
be  bounded  below  by  a  horizon  in  which  the  ground  is  very 
close,  the  comparatively  small  openings  which  once  existed 
having  been  cemented  by  the  material  deposited  during  the 
first  concentration  by  the  ascending  water. 

DEPTH  OF  THE  EFFECT  OF  DESCENDING  WATERS. 
For  the  depth  to  which  downward-percolating  waters  produce 
an  effect  there  can  be  no  doubt  of  their  importance  in  the  pro- 
duction of  ore-deposits.  The  only  question  which  remains  open 
is  the  depth  to  which  ^this  process  is  effective.  This  varies 
greatly  in  different  districts,  and  in  different  mines  of  the  same 
district.  In  general,  the  effect  is  likely  to  be  deep-seated  in 
proportion  as  the  lode  worked  is  on  high  ground  (see  pp.  417- 
418).  Also,  in  arid  regions  the  level  of  groundwater  is  deeper 
below  the  surface  than  in  humid  regions.  Moreover,  the  pro- 
cess of  denudation  is  slower,  so  that  the  downward-moving  wa- 

*  "Lake  Bonneville,"  by  G.  K.  Gilbert,  Mon.  U.  S.  GeoL  Surv.,  No.  1, 
1890.  "Geological  History  of  Lake  Lahontan,  a  Quaternary  Lake  of  South- 
western Nevada,"  by  I.  C.  Eussell,  Mon.  U.  &  GeoL  Surv.,  No.  11,  1885. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.      381 

ters  have  both  a  wider  zone  in  which  to  work  above  the  level  of 
groundwater  and  a  longer  time  in  which  to  work  upon  a  given 
horizon,  and  thus  in  such  regions  the  oxides  and  carbonates  are 
likely  to  occupy  a  considerable  zone.  This  is  very  well  illus- 
trated by  the  copper-mines  of  Arizona  and  JSTew  Mexico,  and 
by  the  colorados  of  the  silver-gold  deposits  in  various  arid  re- 
gions. In  humid  regions,  upon  the  other  hand,  the  level  of 
groundwater  is  likely  to  be  near  the  surface.  If  this  be  com- 
bined with  marked  relief  so  that  denudation  is  rapid,  the  pro- 
cesses of  oxidation  and  carbonation  may  not  be  nearly  so  com- 
plete above  the  level  of  groundwater.  Indeed,  in  many  cases 
erosion  may  be  so  rapid  that  the  sulphurets  do  not  have  time 
for  oxidation,  and  they  may  extend  nearly  or  quite  to  the  sur- 
face, although  in  such  cases  they  are  likely  to  be  enriched,  as 
explained  (pp.  3 54-3 5 7),  and  it  is  very  uncommon  to  find  a  de- 
posit in  which  no  effect  of  descending  waters  can  be  discovered. 

It  has  already  been  seen  that  the  level  of  groundwater  may 
vary  from  the  surface  to  300  meters  or  more  below  the  surface. 
Hence  it  is  certain  that,  from  the  surface  to  300  meters  below 
the  surface,  the  underground  waters  may  be  a  potent  factor  in 
the  production  of  the  rich  ore-deposits.  The  deposits  in  this 
belt  are  particularly  profitable,  not  only  because  of  the  accessi- 
bility of  the  material,  but  because  of  the  fact  that  there  is  no 
expense  for  pumping;  and  furthermore,  the  products  are  in 
forms  which  in  most  cases  are  easily  reducible.  This  may  be 
illustrated  by  the  gold  and  silver  deposits.  In  the  former,  the 
native  gold  is  free  from  its  entanglement  of  sulphurets  and  tel- 
lurides;  in  the  latter  the  silver  is  largely  in  the  form  of  the 
readily  extracted  chloride,  or  in  some  instances  as  native  silver. 

Up  to  this  point  there  will  be  no  disagreement  on  the  part  of 
any  one.  But  the  question  now  arises  as  to  the  depths  below 
the  level  of  groundwater  to  which  descending  waters  produce 
their  effects.  This  is  a  question  to  be  answered  not  by  deduc- 
tion, but  by  observation.  Even  Posepny,  who  emphasizes  the 
effect  of  ascending  waters,  agrees  that  oxidized  products  are  the 
evidence  of  the  work  of  vadose  circulation,  or  the  circulation 
of  lateral  and  downward-moving  waters.  *  Furthermore,  Posepny 

*  "Genesis  of  Ore-Deposits,"  by  F.  Posepny  (Discussion),  this  volume,  p.  237. 


382       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

agrees  that  the  iron-mines  of  the  Lake  Superior  region,  which 
are  oxidized  products,  have  been  produced  by  downward-mov- 
ing waters.  A  number  of  these  mines  have  been  worked  to  a 
depth  of  500  or  more  meters  below  the  level  of  groundwater. 
It  is,  therefore,  perfectly  clear  in  these  cases  that  the  down- 
ward-percolating waters  produce  an  oxidizing  effect  to  a  depth 
of  at  least  500  meters  below  the  level  of  groundwater.  And 
this  is  so  in  a  region  in  which  the  level  of  groundwater  is  rela- 
tively near  the  land  surface,  and  which  is  not  mountainous. 
In  various  other  regions  oxidized  products  are  also  found  to  a 
very  considerable  depth  below  the  level  of  the  groundwater. 

In  the  San  Juan  district  of  Colorado,  in  the  Gold  King  mine, 
at  a  vertical  depth  of  more  than  300  meters,  "  the  ore  taken  out 
is  characterized  by  decomposition,  being  stained  with  iron  oxide, 
and  showing  almost  no  metallic  sulphides."*  The  author  does 
not  state  how  far  this  is  below  the  level  of  groundwater,  but 
merely  says  that  the  water-level  is  deep.  Many  other  veins 
contain  sulphurets,  which  extend  nearly  to  the  surface.  In  the 
Cripple  Creek  district  of  Colorado  and  the  Judith  mountains 
of  Montana — humid  areas — oxidized  products  are  found  to  a 
depth  of  125  meters.  The  workings  at  the  time  when  Penrose, 
Weed  and  Pirssonf  examined  the  districts  had  not  extended 
beyond  this  depth ;  and  therefore  we  have  no  knowledge  as  to 
the  depth  at  which  the  last  of  the  oxidized  products  will  be 
found,  or  as  to  the  depth  to  which  the  sulphides  and  tellurides 
have  been  reacted  upon  and  enriched  by  the  downward-moving 
solutions  from  above.  This  belt  of  enriched  material  may  be  of 
even  greater  depth  than  that  of  the  oxidized  products. 

As  has  already  been  shown  (pp.  356-371),  where  the  ores  are 
predominantly  lean  sulphides  in  the  lower  workings  of  the  mines, 
these  react  upon  the  downward-moving  oxidized  salts  of  the 
valuable  metals,  and  thus  produce  rich  sulphurets.  It  is,  there- 
fore, clear  that  descending  waters  produce  enrichment  below 
the  level  at  which  oxidized  products  are  found. 

*  "  Preliminary  Report  on  the  Mining  Industries  of  the  Telluride  Quadrangle, 
Colorado,"  by  C.  W.  Purington,  18th  Ann.  Eept.  U.  S.  Geol.  Surv.,  pt.  iii.,  1896- 
97,  pp.  825-826. 

|  " Mining  Geology  of  the  Cripple  Creek  District,"  by  R.  A.  F.  Penrose,  Jr., 
16th  Ann.  Eept.  U.  S.  Geol.  Surv.,  pt.  ii.,  1894-95,  p.  129.  "Geology  and  Mineral 
Resources  of  the  Judith  Mountains  of  Montana,"  by  W.  H.  Weed  and  L.  V. 
Pirsson,  18th  Ann.  Eept.  U.  S.  Geol.  Surv.,  pt.  iii.,  1896-97,  p.  592. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       383 

Our  conclusion  is,  that  we  have  positive  evidence  that  the  belt  in 
which  descending  waters  are  effective  in  producing  rich  secondary 
concentrates,  as  explained  on  pp.  354—378,  extends  to  very  considerable 
depths. 

ILLUSTRATIONS  OF  SECONDARY  ENRICHMENT  AND  DIMINUTION 
OF  RICHNESS  WITH  DEPTH. 

The  processes  have  now  been  explained  by  means  of  which  a 
rich  upper  belt  may  be  produced.  If  the  argument  be  correct, 
it  is  an  inference  from  this  that  ore-deposits  which  have  under- 
gone a  second  concentration  are  likely  to  diminish  in  richness 
with  depth,  provided  a  considerable  belt  be  considered.  It  re- 
mains to  give  instances,  the  facts  of  which  confirm  the  actual- 
ity of  the  processes  explained,  and  illustrate  diminution  of  rich- 
ness with  depth. 

At  Ducktown,  Tenn.,  at  the  level  of  groundwater  a  belt  of 
rich  black  copper  (copper-glance)  appears,  which  varies  from  less 
than  one  to  about  two  and  one-half  meters  in  thickness.  Above 
this  belt  is  gossan  very  poor  in  copper,  below  it  is  a  very  low 
grade  cupriferous  pyrrhotite.*  In  this  instance  it  can  hardly 
be  doubted  that  originally  the  lean  cupriferous  pyrrhotite  ex- 
tended not  only  to  the  present  surface,  but  probably  much 
higher  than  this.  The  downward  moving  waters  have  trans- 
ported copper  to  its  present  locus  near  the  level  of  groundwater. 
Here  the  copper  salts  have  reacted  upon  the  iron  sulphide  and 
produced  rich  sulphurets. 

A  case  which  has  been,  perhaps,  more  closely  studied  than 
that  of  any  other  in  the  United  States  is  that  of  the  deposits  of 
Butte,  Montana.  Here  Douglas  states  that  rich  oxysulphurets 
are  found  near  the  surface.  These  rich  oxysulphurets  occur  in 
greatest  depths  and  richness  on  the  summit  of  the  hill, "  where 
it  seems  as  if  the  copper,  leached  out  of  the  400  feet  of  depleted 
vein,  had  been  concentrated  in  the  underlying  ore,  and  had 
thus  produced  a  zone  of  secondary  ore  about  200  deep,  which 
contains,  as  might  be  expected,  about  thrice  its  normal  copper- 
contents."! 

*  "  The  Persistence  of  Ores  in  Lodes  in  Depth,"  by  W.  P.  Blake.  Eng.  and 
Min.  Jour. ,  vol.  1  v. ,  1 893,  p.  3.  Also,  *  *  The  Ducktown'  Ore-deposits  and  the  Treat- 
ment of  the  Ducktown  Copper-ore,"  by  C.  Henrich,  Trans.,  xxv.,  1896,  206-209. 

|  "The  Copper  Kesources  of  the  United  States,"  by  Jas.  Douglas,  Trans.,  xix., 
1891,  p.  693. 


384      SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

Emmons  says  of  the  Butte  deposits:* 

"Secondary  deposition,  or  transposition  of  already  deposited  minerals,  has  played 
an  unusually  important  role.  In  the  case  of  the  copper  veins  it  has  not  been  con- 
fined to  the  oxidizing  action  of  surface  waters,  which  has  resulted  in  an  impover- 
ishment of  the  o-re-bodies,  but  below  the  zone  of  oxidation  it  has  resulted  in  the 
formation  of  the  richer  copper  minerals  bornite,  chalcocite  and  covellite,  in  part 
at  least  by  the  breaking  up  of  the  original  chalcopyrite.  Unusual  enrichment  of 
the  middle  depths  of  the  lodes  has  thus  been  caused.  Whether  the  two  processes 
of  impoverishment  and  enrichment  have  been  differing  phases  of  the  action  of 
descending  waters,  or  whether  the  latter  may  have  been  a  later  result  of  the  rhy- 
olite  intrusion,  has  not  yet  been  definitely  decided.  It  is,  however,  fairly  well 
determined  that  the  enrichment  of  the  copper  deposits  is  so  closely  associated  with 
the  secondary  faulting  that  it  may  be  considered  to  be  a  genetic  result  of  it." 

Brown  states  of  the  same  area  that  oxidized  products  extend 
to  the  level  of  groundwater.  These  oxidized  products,  accord- 
ing to  Brown,  promptly  change  at  water  level  to  normal  sul- 
phurets.  "  There  follows  below  a  region  of  varying  height,  of 
valuable  rock,  which  again  slowly  deteriorates  in  depth ;  this 
deterioration,  however,  being  so  retarded  finally  as  to  be 
scarcely  appreciable. "f  He  further  says  that  above  the  level 
of  groundwater  is  gossan  "  carrying  high  values  in  silver,  and 
particularly  in  gold."J  Thus  at  Butte  we  have  in  the  belt  above 
the  level  of  groundwater  enrichment  in  silver  and  gold  and 
depletion  in  copper  as  compared  with  the  material  below  the 
level  of  groundwater ;  and  at  and  below  the  level  of  ground- 
water  we  have  rich  sulphides  of  copper  which  grade  into  leaner 
sulphurets.  In  the  case  of  the  Butte  deposits  it  can  hardly  be 
doubted  that  the  comparatively  lean  sulphides  in  the  deeper 
workings  represent  the  product  of  a  first  concentration,  and 
that  the  modifications  of  this  material  found  above  and  below 
the  level  'of  groundwater  represent  the  work  of  downward 
moving  waters.  To  account  for  the  high  values  of  gold  and 
silver  above  the  level  of  groundwater,  one  must  suppose  that 
this  belt  has  received  contributions  of  these  metals  from  the 
upward  extension  of  the  veins  which  have  now  been  removed 
by  erosion.  The  great  richness  of  the  copper  below  the  level 
of  groundwater  Douglas  clearly  attributes  to  the  downward 

*  "  Economic  Geology  of  the  Butte  District,"  by  S.  F.  Emmons,  Geol.  Atlas  of 
the  U.  S.,  Butte  special  folio,  Montana,  1897. 

t  "The  Ore-deposits  of  Butte  City,"  by  E.  G.  Brown,  Trans.,  xxiv.,  1895,  p.  556. 
J  Brown,  loc.  ciL,  p.  555. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       385 

transportation  of  the  material  from  the  depleted  copper  veins. 
However,  a  part  of  this  material  was  doubtless  derived  from 
an  upward  extension  of  these  veins  precisely  as  in  the  case  of 
the  gold  and  silver.  For  my  own  part  I  have  little  doubt  that 
the  precipitation  of  the  rich  sulphides  was  produced  by  reac- 
tion upon  the  lean  sulphurets,  as  given  in  the  equations  pp. 
356,  366-367.  Indeed,  these  equations  were  written  out  with 
reference  to  the  facts  of  the  Butte  deposits. 

Penrose  cites  the  Arizona  copper  deposits  as  instances  of 
secondary  concentration.  These  deposits  he  regards  as  pro- 
duced by  leaching  of  the  copper  from  a  lean  copper-bearing 
pyrite,  and  its  segregation  at  the  places  where  the  rich  ores 
occur.  In  this  process  Penrose,  however,  says  that  the  volume 
of  the  deposit  must  be  decreased ;  but  he  makes  the  point  that 
the  smaller  amount  of  the  rich  product  is  more  valuable  than 
a  larger  lean  deposit,  because  more  easily  mined  and  more 
readily  reduced.* 

This  process  of  concentration  is  further  described  by  Douglas, 
who  notes,  also,  that  the  changes  have  resulted  in  the  produc- 
tion of  enriched  sulphides  from  very  lean  sulphides  in  the 
Copper  Queen  mine.  Here,  according  to  Douglas,  a  large 
very  low-grade  copper-bearing  pyrite  deposit  running  from  the 
200-  to  the  400-foot  level  contains  rich  oxysulphides  and  black 
sulphides  on  the  outside,  and  in  the  interior  is  mainly  lean 

pyrite.f 

The  original  material  in  the  Arizona  locality  is  as  plainly  a  lean 
cupriferous  pyrites  as  in  Tennessee.  Here,  however,  on  account 
of  the  peculiar  climatic  conditions  the  alterations  have  not  ex- 
tended to  a  uniform  depth.  Instead  of  the  rich  belt  being  a 
sheet  which  diminishes  in  richness  below,  it  occurs  in  a  zone 
about  the  entire  residual  cupriferous  pyrites  masses.  The  prin- 
ciples of  concentration  are,  however,  identical,  and  the  rich 
sulphurets  are  unquestionably  due  to  reactions  between  the  ox- 
idized salts  and  the  lean  sulphides.  The  rich  oxidized  products 
of  this  area,  doubtless,  were  produced  directly  from  the  enriched 
sulphurets.  Therefore,  in  the  formation  of  the  rich  oxidized 

*  "The  Superficial  Alteration  of  Ore-deposits,"  by  K.  A.  F.  Penrose,  Jour,  of 
Geol,  vol.  ii.,  1894,  pp.  306-308. 

f  "The  Copper  Queen  Mine,  Arizona,"  by  Jas.  Douglas,  Trans.,  xxix.,  1900, 
p.  532. 


386      SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

products  there  were  two  stages  of  alteration ;  first,  the  produc- 
tion of  rich  sulphurets  by  the  reaction  of  oxidized  products 
upon  the  lean  pyritiferous  material,  and  after  that  oxidation  of 
the  rich  sulphurets,  which  occur  partly  in  situ,  has  also,  doubt- 
less, taken  place  with  more  or  less  of  transfer  of  material  from 
one  place  to  another. 

An  excellent  illustration  of  an  enriched  upper  belt  in  the 
case  of  gold  is  furnished  by  the  gold-quartz  veins  of  Grass  Val- 
ley, California,  where,  according  to  Lindgren,  the  decomposed 
belt  of  weathering  about  50  meters  deep  contains  "  from  $80 
to  $300  per  ton,  while  the  average  tenor  in  depth  is  from  $20 
to  $30."*  Furthermore,  the  rich  50  meters,  which  contains 
from  four  to  ten  times  as  much  gold  as  the  sulphurets  below 
the  level  of  groundwater,  is  depleted  in  silver.  However,  in 
some  veins  the  sulphurets  extend  almost  to  the  surface.  Lind- 
gren further  states  that  the  sulphurets  below  the  level  of  ground- 
water  continue  with  undiminished  richness  to  a  depth  of  500 
or  more  meters. f  He  adds  that  the  California  region  is  one  in 
which  denudation  has  extended  to  a  depth  of  500  to  1500  or 
more  meters. {  From  these  facts  it  is  highly  probable,  as  sug- 
gested by  Lindgren,  that  the  sulphurets  similar  to  those  below 
the  level  of  groundwater  were  deposited  above  the  present 
surface  of  the  country.  If  this  were  the  case  the  only  possible 
explanation  of  the  belt  of  weathering  rich  in  gold  and  depleted 
in  silver  is  that  descending  waters  have  abstracted  a  large  part 
of  the  gold  from  the  500  to  1500  meters  removed  by  erosion, 
and  have  deposited  it  in  the  belt  of  weathering.  Its  precipita- 
tion there  was,  doubtless,  mainly  due  to  the  reaction  of  the  ox- 
idized products  upon  the  sulphides,  producing  sulphurets  richer 
in  gold.  Later,  these  rich  sulphurets  have  been  oxidized,  leav- 
ing the  enriched  belt  of  free  gold.  The  silver  apparently  has 
been  transported  downward  to  a  greater  extent  in  this  belt. 
One  would  expect  that  correlative  with  the  belt  above  the  level 
of  groundwater  poor  in  silver,  there  would  be  a  belt  at  and 
below  the  level  of  groundwater  richer  in  silver  than  that  above. 
Upon  this  point  Lindgren  does  not  give  us  information. 

*  "The  Gold-quartz  Veins  of  Nevada  City  and  Grass  Valley,  California,"  by 
Waldemar  Lindgren,  17th  Ann.  Eept.  U.  S.  Geo.  Surv.,  1895-96,  pt.  ii.,  p.  128, 1896. 
f  Lindgren,  loc.  cit.,  p.  163. 
J  Lindgren,  toe.  cit.,  p.  183. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       387 

Another  very  interesting  case  of  the  richness  of  the  belt  of 
weathering  in  gold,  as  compared  with  the  unaltered  sulphides 
below,  is  furnished  by  the  Australian  gold-fields,  where  the  belt 
above  the  level  of  groundwater  is  several  times  as  rich  as  the 
unaltered  tellurides  and  sulphides  below;  some  mining  men 
say  ounces  above  to  pennyweights  below.* 

This  rich  belt  is  from  50  to  400  feet.  In  a  portion  of  the 
mines  of  some  districts — for  example,  the  Kalgoorlie  district — 
when  the  bottom  of  the  oxidized  zone  is  reached,  the  ores  are 
so  lean  as  to  be  valueless,  so  that  mines  which  were  profitable 
in  the  weathered  zone  were  not  profitable  below  that  zone.f 
Many  of  the  mines  of  that  district,  however,  are  profitable  below 
the  weathered  zone.  If  it  had  not  been  for  the  secondary  enrich- 
ment of  denudation  and  downward  transportation  of  material, 
many  of  the  mines  would  not  have  been  exploited,  although 
Hoover  thinks,  that  in  this  strange  country,  the  downward 
concentration  is  more  mechanical  than  chemical.  Thus  the 
secondary  concentration  by  descension  is  no  less  an  important 
part  of  the  genesis  of  the  gold-ores  of  Australia  than  the  first 
concentration  by  ascending  waters. 

The  lead-  and  zinc-deposits  of  the  Mississippi  valley  (see  pp. 
357-364),  are  believed  to  be  clear  cases  of  the  importance  of 
the  action  of  descending  waters.  This  has  already  been  shown 
for  "Wisconsin.  In  the  lead  and  zinc  districts  of  Missouri  the 
galena  is  at  a  high  horizon,  and  the  sphalerite  at  a  low  horizon, 
precisely  as  in  Wisconsin.  Moreover,  the  arrangement  of  the 
different  kinds  of  materials  in  the  veins  is  very  similar  to  that 
in  Wisconsin,  the  order  of  deposition  of  the  minerals  from  above 
down  being  (1)  blende,  (2)  galena,  (3)  pyrite.  This  corresponds 
to  the  order  of  the  more  important  deposits  in  Wisconsin,  ex- 
cept that  before  the  blende,  marcasite  formed.  (See  p.  359.) 
Lead-bearing  ores  in  Missouri  occur  in  the  Cambrian  lime- 
stones; zinc-ores  occur  in  the  sub-Carboniferous  limestones; 
and  lead-  and  zinc-ores  occur  in  the  Lower  Silurian  rocks.  J 


*  ''The  Genesis  of  Certain  Auriferous  Lodes,"  by  J.  K.  Don,  Trans.,  xxvii., 
1898,  p.  596. 

f  "The  Alteration  of  Western  Australian  Ore-deposits,"  by  H.  C.  Hoover, 
Trans.,  xxviii.,  1899,  pp.  762-764. 

I  "The  Lead  and  Zinc  Deposits  of  the  Mississippi  Valley,"  by  W.  P.  Jenney, 
Trans.,  xxii.,  1894,  pp.  187-188,  197,  199-200. 

25 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

In  Wisconsin  the  ores  occur  mainly  "  in  the  Galena,  Trenton, 
and,  subordinately,  Lower  Magnesian  limestones."*  However, 
in  all  of  these  districts  the  ores  which  have  been  taken  out  are 
very  largely  above  the  50  meter  level.  The  probable  explana- 
tion of  these  relations  is  as  follows:  The  ores  were  disseminated 
in  various  sedimentary  strata,  and  possibly,  also,  to  some  ex- 
tent in  the  pre-sedimentary  rocks.  They  were  concentrated 
through  a  comparatively  wide  vertical  range  by  ascending 
waters.  But  the  position  of  the  rich  ores  near  the  surface  is 
due  to  secondary  concentration  by  descending  waters,  concen- 
tration going  on  pari-passu  with  erosion  in  such  a  manner  that 
the  rich  ores  are  continuously  deposited  above  and  below  the 
level  of  groundwater,  as  explained  in  the  previous  pages.  As 
denudation  passes  downward,  and  thus  the  level  of  groundwater 
descends,  the  horizon  of  rich  concentrates  also  descends. 

The  Leadville  deposits  furnish  an  instance  of  the  decrease  of 
the  richness  in  silver  with  depth.  Emmons  says  :  "  There  is  a 
fair  foundation  for  the  generalization  that  in  the  deposits,  as 
developed  at  the  time  of  this  investigation,  the  ores  were  grow- 
ing poorer  in  silver  as  exploration  extended  farther  from  the 
surface,  "f 

Another  case  of  the  diminution  of  richness  of  sulphurets 
with  depth  is  furnished  by  the  nickel  mine  of  Lancaster  Gap, 
which,  however,  were  not  worked  beyond  a  depth  of  about  75 
meters,  presumably  because  "  the  ores  decreased  in  richness  as 
depth  was  attained."! 

In  addition  to  these  specific  instances  of  the  production  of  a 
rich  upper  belt,  some  general  statements  have  been  made  which 
need  to  be  referred  to.  One  of  these  is  made  by  Douglas  in 
reference  to  sulphuret  mines  as  a  whole.  Says  he,  in  the  con- 
clusion of  his  discussion  as  to  the  copper  resources  of  the 
United  States,  with  reference  to  the  various  Appalachian  de- 
posits, "  Like  all  sulphuret  mines,  they  became  poorer  as  depth 
was  attained." § 

*  "Geology  of  Wisconsin,"  vol.  iv.,  p.  451. 

t  "The  Geology  and  Mining  Industry  of  Leadville,"  by  S.  F.  Emmons,  Mon. 
U.  S.  Geol.  Surv.,  No.  12,  1886,  pp.  554-555. 

J  "The  Nickel  Mine  at  Lancaster  Gap,  Pennsylvania,"  by  J.  F.  Kemp,  Trans. 
xxiv.,  1895,  pp.  626,  884. 

$  "  The  Copper  Eesources  of  the  United  States,"  by  Jas.  Douglas,  Trans.,  xix., 
1891,  p.  694. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       389 

Penrose,*  in  1894,  discussed  the  superficial  alteration  of  ore- 
deposits.  He  says : 

"As  a  result  of  these  various  changes,  certain  materials  are  sometimes  leached 
from  the  upper  parts  of  ore-deposits,  which  have  become  porous  by  alteration,  and 
carried  down  to  the  less  pervious  unaltered  parts.  Here  they  are  precipitated  by 
meeting  other  solutions  or  in  other  ways,  and  hence  the  richest  bodies  of  ore  in  a 
deposit  often  occur  between  the  overlying  altered  part  and  the  underlying  unal- 
tered part.  This  is  not  always  the  case,  but  it  is  true  of  some  copper,  silver,  iron 
and  other  deposits,  "f 

De  Launay,J  in  1897,  emphasizes  the  frequent  occurrence  of 
rich  products  near  the  surface,  which  in  some  cases  are  oxi- 
dized products,  and  in  others  are  sulphides.  He,  however,  ex- 
plains the  richness  of  the  deposits  by  the  abstraction  of  more 
soluble  material.  This  frequently  results  in  transforming  a  low 
grade  product  into  a  rich  ore.  By  this  process  a  poor  sulphide 
may  be  changed  to  a  rich  sulphide,  as,  for  instance,  cuprifer- 
ous pyrites  or  chalcopyrite  may  be  transformed  to  covellite  or 
chalcocite  by  abstraction  of  iron  sulphide.  It  is  a  natural  de- 
duction from  De  Launay's§  explanation,  that  the  volume  of  the 
material  is  decreased,  although  he  does  not  make  this  point. 

De  Launay  further  emphasized  the  point  that  the  ore-material 
of  veins  may  have  been  repeatedly  transferred  from  one  place 
to  another,  and  suggests  that  a  part  of  the  material  now  found 
in  veins  may  have  been  transferred  from  vein  material  which 
was  once  above  the  present  surface  of  denudation. 

While  it  is  believed  to  be  a  very  general  case,  if  a  long  enough 
scale  be  used,  that  ore-deposits  diminish  in  richness  with  depth, 
it  is  well-known  that  above  the  level  of  groundwater  the  val- 
uable materials  may  be  almost  wholly  dissolved  and  deposited 
at  or  below  the  level  of  groundwater  by  the  reactions  above 
stated,  as  at  Ducktown,  Tennessee,  or  partly  dissolved  and 
transported  below,  as  at  Butte,  Montana.  Thus,  for  a  certain 
depth  the  ores  may  increase  in  richness.  This  exception,  how- 
ever, does  not  affect  the  common  rule  as  to  diminution  of  rich- 
ness with  increasing  depth. 

*  "The  Superficial  Alteration  of  Ore-deposits,"  by  K.  A.  F.  Penrose,  Jr., 
Jour,  of  GeoL,  vol.  ii.,  1894,  pp.  288-317. 

f  Penrose,  cif.,  p.  294. 

I  "Contribution  a  1' Etude  des  Gites  Me*talliferes,"  by  M.  L.  De  Launay,  An- 
notes  des  Mines,  9th  ser.,  vol.  xii.,  1897,  pp.  151-152. 

I  De  Launay,  dt.t  p.  194. 


390       SOME   PRINCIPLES   CONTROLLING   DEPOSITION    OF    ORES. 


GENERAL. 

It  is  apparent  from  the  foregoing  that  there  has  been  a  gen- 
eral understanding  that  a  rich  upper  belt  has  been  produced  in 
many  ore-deposits.  Le  Conte,*  who  appreciated  this,  suggests 
that  the  rich  belt  may  be  explained  by  supposing  that  precipi- 
tation by  ascending  waters  does  not  occur  at  great  depth, 
because  the  solutions  do  not  get  saturated  until  comparatively 
near  the  level  of  underground  water.  However,  it  is  to  be 
remembered  that  the  upper  part  of  a  fissure  is  that  receiv- 
ing abundant  lateral  waters  which  have  taken  a  comparatively 
brief  journey  under  conditions  of  low  pressure  and  tempera- 
ture; whereas  the  solutions  lower  down  have  taken  a  longer 
journey  under  conditions  of  high  pressure  and  temperature. 
In  this  connection  it  might  be  further  supposed  that  the  vary- 
ing richness  could  be  partly  explained  by  the  lessening  temper- 
ature and  pressure  of  the  rising  solutions.  But  if  this  be  true, 
one  would  expect  the  most  insoluble  constituent  to  be  precipi- 
tated deepest  down.  In  the  case  of  the  lead-zinc-iron  deposits 
this  would  make  the  galena  most  abundant  at  depth,  the  sphal- 
erite most  abundant  at  a  higher  level,  and  the  iron  sulphide  the 
dominating  constituent  at  the  highest  levels.  In  the  case  of 
the  copper-iron  deposits,  the  rich  sulphides  of  copper  would  be 
in  the  lower  levels  and  the  cupriferous  pyrites  at  the  higher 
levels. 

As  already  seen,  Penrose's  explanation  of  the  phenomenon  of 
a  rich  upper  belt  is  that  the  concentrates  have  been  produced 
by  downward  transportation  and  precipitation  by  meeting 
other  solutions.  De  Launay's  explanation  of  the  phenomena 
is  enrichment  by  the  abstraction  of  the  more  soluble  and  less 
valuable  material,  thus  producing  a  smaller  quantity  of  rela- 
tively rich  product. 

While  the  reactions  between  the  oxidized  products  and  the 
sulphides  are  emphasized,  and  are  believed  to  be  the  most  fun- 
damental and  widespread,  my  own  explanationf  is,  mainly, 

*  Le  Conte,  loc.  cit.,  p.  12. 

f  Just  as  I  am  sending  this  paper  to  the  press  in  its  revised  form  (a  preliminary 
proof  edition  was  published  and  distributed  in  February,  1900),  I  am  in  receipt 
of  a  paper  upon  the  "  Enrichment  of  Mineral  Veins  by  Later  Metallic  Sul- 
phides," by  Walter  Harvey  Weed  (Bull.  Geol.  Soc.  Am.,  vol.  xi.,  pp.  179-206). 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       391 

that  oxidized  soluble  products  are  produced  in  the  belt  of 
weathering;  that  these  in  situ  or  lower  down  react  upon  the 
lean  sulphides.  In  this  way  a  belt  of  rich  sulphurets  is  formed. 
Later,  in  consequence  of  denudation,  these  rich  sulphides  pass 
into  the  belt  of  weathering.  Here  they  are  again  exposed  to 
the  oxidizing  forces,  where  in  situ  they  are  largely  transformed 
to  oxides,  carbonates,  etc.,  and  a  belt  of  rich  oxidized  products 
above  the  groundwater  is  formed.  However,  in  part,  when 
oxidized,  they  are  taken  into  solution,  again  transported  down- 
ward, and  again  react  upon  the  sulphurets.  In  arid  regions 
where  the  amount  of  downward-moving  water  is  small,  the 
oxidized  products  formed  from  the  rich  sulphurets  are  likely 
to  remain  in  large  part  in  situ.  Where,  upon  the  other  hand, 
water  is  abundant  the  sulphides  when  oxidized  are  in  large 
measure  likely  to  be  carried  downward,  and  again  react  upon 
the  sulphides  below  and  further  broaden  and  enrich  the  belt  of 
sulphides.  Thus,  under  different  climatic  conditions,  we  may 


This  paper  strongly  emphasizes  the  enrichment  of  an  upper  belt  through  the 
action  of  descending  waters.  Moreover,  the  paper  includes  the  reactions  of  the 
oxidized  products  upon  the  poor  sulphurets,  thus  producing  rich  sulphurets. 
Many  occurrences  are  given  which  illustrate  the  enrichment  of  sulphides  by 
descending  waters,  including  copper,  silver  and  zinc  deposits.  Some  of  the 
illustrations  given  by  Mr.  Weed  I  also  have  used.  Others  are  additional  to 
those  given  by  me.  In  general  it  may  be  said  that  Mr.  Weed's  paper  and  that 
part  of  my  own  which  deals  with  secondary  enrichment  by  descending  waters  are 
supplemental  and  support  each  other  ;  since  each  did  his  work  and  arrived  at  his 
conclusions  in  entire  ignorance  of  the  fact  that  the  other  was  working  along  a 
similar  line. 

Upon  one  point  only  is  there  difference  of  opinion  between  us.  Mr.  Weed,  in 
his  general  statement,  says  that  the  part  of  the  veins  "below  the  permanent 
groundwater  level  consists  of  the  unaltered  sulphides  which  compose  the  orig- 
inal ore  of  the  vein.  This  part  constitutes  the  zone  of  primary  sulphide  ore" 
(p.  181).  However,  while  Weed  makes  the  above  general  statement,  he  appears 
to  appreciate  that  in  individual  cases  rich  oxidized  sulphides  may  be  produced 
below  the  permanent  groundwater  level,  for  he  says  that  at  Elkhorn,  Montana, 
this  level  is  only  185  to  210  meters  below  the  surface,  whereas  the  sulphides 
enriched  by  descending  waters  extend  to  the  depth  of  600  meters  (p.  204).  If 
my  reasoning  be  correct,  the  zone  of  secondary  enrichment  by  descending  waters 
will  ordinarily  extend  far  below  the  permanent  groundwater  level,  in  many 
instances  to  the  depth  of  several  hundred  meters.  Indeed,  not  only  the  Montana 
instance,  but  other  illustrations  given  by  Mr.  Weed  confirm  this  conclusion.  In 
the  pyrite  deposits  of  Spain  and  Portugal,  described  by  Vogt,  the  ores  decrease 
in  richness  to  the  depth  of  350  meters  (p.  198).  Also  in  Norway,  if  I  under- 
stand Mr.  Weed  correctly,  the  diminution  of  richness  of  the  copper  deposits  with 
depth  extends  from  350  meters  to  over  700  meters. 


392       SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

have  a  rich  oxidized  zone,  a  rich  sulphide  zone,  or  both,  in 
varying  proportion. 

While  the  reaction  between  the  oxidized  products  and  the 
sulphides  has  been  strongly  emphasized  in  this  paper  because 
it  is  believed  to  be  the  most  fundamental  of  the  causes  pro- 
ducing a  rich  upper  belt,  it  is  understood  that  other  factors 
may  also  help  in  this  process.  As  already  pointed  out,  reduc- 
tion and  precipitation  of  the  metals  of  descending  solutions 
may  take  place  through  the  agency  of  organic  matter  or  other 
reducing  materials  contained  in  the  rocks,  or  by  meeting 
ascending  solutions  carrying  precipitating  agents ;  also  near 
the  surface  more  than  an  average  amount  of  original  precipi- 
tates from  ascending  solutions  is  a  possibility  in  some  cases. 
(See  pp.  377-378.) 

Summarizing,  it  appears  to  me,  therefore,  that  the  existence 
of  a  rich  upper  belt  in  many  deposits,  and  the  frequent  diminu- 
tion of  richness  of  the  ores  in  passing  downward  from  the  surface 
to  some  distance  below  the  level  of  groundwater,  cannot  be 
explained  as  the  work  of  ascending  waters  alone  or  as  the  work 
of  descending  waters  alone ;  but  is  fully  explained  as  due  to 
the  work  of  ascending  and  descending  waters  combined. 
Ascending  waters  produce  a  first  concentration.  A  second 
concentration  by  descending  waters  produces  the  rich  products. 
Moreover,  these  rich  products  are  found  in  the  few  meters  or 
few  hundred  meters  of  the  outer  crust  of  the  earth.  When  it 
is  remembered  that  the  greater  part  of  the  ores  which  have 
yet  to  be  abstracted  from  the  earth  will  come  from  the  first  500 
or  700  meters,  and  when  it  is  further  considered  that  the  effect 
of  descending  waters  may  be  felt  to  these  depths,  it  becomes 
evident  that  the  process  of  second  concentration  by  descending 
waters  is  a  very  important  one  indeed,  so  far  as  the  economic 
value  of  ore-deposits  is  concerned.  Indeed,  as  a  result  of  it 
there  is  concentrated  in  the  extreme  outer  shell  of  the  crust  of 
the  earth  a  large  portion  of  the  products  which  during  the 
first  concentration  may  in  many  cases  have  been  distributed 
over  1500  or  3000  meters  or  more,  but  which  have  now  been 
largely  removed  by  erosion.  "We  therefore  conclude  that,  for 
a  large  class  of  ore-deposits,  a  second  concentration  by  descend- 
ing waters  cannot  be  said  to  be  one  whit  less  important  in  the  genesis 
of  ores  than  a  first  concentration  by  ascending  waters. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OP    ORES.       393 

It  follows  from  the  foregoing  that  one  of  the  most  impor- 
tant classes  of  ore-deposits  is  that  produced  by  the  joint  action 
of  ascending  and  descending  waters. 

THE  PRECIPITATION  OF  ORES  BY  DESCENDING  WATERS  ALONE. 

For  the  sake  of  simplicity  and  continuity  of  exposition,  the 
effects  produced  by  descending  waters  have  been  applied  to  de- 
posits which  have  been  first  concentrated  by  ascending  waters. 
However,  it  is  perfectly  clear  that  a  concentration  by  descend- 
ing waters  alone  may  be  adequate  to  produce  ore-deposits. 
Indeed,  this  is  definitely  known  to  be  true  of  some  of  the  most 
important  ore-deposits,  as  for  instance  many  of  the  iron-ores. 
A  conspicuous  case  is  that  of  the  Lake  Superior  iron-ores,  which 
very  well  illustrate  the  process  of  formation  of  ores  of  this  class. 
Since  the  genesis  of  the  Lake  Superior  iron-ores  is  fully  dis- 
cussed by  me  in  the  Twenty-first  Annual  Report  of  the  U.  S. 
Geological  Survey,  this  class  of  ores  is  not  further  discussed  here. 

SPECIAL  FACTORS  AFFECTING  THE  CONCENTRATION  OF  ORES. 

In  Part  I.  it  has  been  shown  that  the  underground  circula- 
tion may  be  effective  to  the  bottom  of  the  zone  of  fracture,  and 
in  Part  II.  it  has  been  seen  that  the  concentration  of  ores  is  an 
orderly  but  complex  process.  However,  the  discussion  has  not 
taken  into  account  a  number  of  the  special  factors  which  affect 
the  concentration  of  ores.  The  general  discussion  may  need 
great  modification  to  adapt  it  to  a  particular  district.  To  illus- 
trate my  meaning,  it  may  be  well  to  consider  some  of  the  ad- 
ditional factors  affecting  the  deposition  of  ores,  and  to  point 
out  the  more  obvious  possible  modifications  of  the  general 
theory  which  may  result  from  them.  The  effect  of  (1)  varia- 
tions in  porosity  and  structure,  (2)  the  character  of  the  topo- 
graphy, and  (3)  physical  revolutions,  will  be  briefly  considered. 

Variations  in  Porosity  and  Structure. 

There  are  many  ways  in  which  variations  in  porosity  and 
structure  may  affect  the  concentration  of  ores  by  influencing 
the  circulation  of  waters.*  The  different  strata  of  the  sediment- 

*  Compare  Emmons's  "Structural  Kelations  of  Ore-Deposits,"  Trans.,  xvi., 
1888,  804-839. 


394      SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

ary  rocks  vary  greatly  in  porosity.  The  igneous  rocks,  and 
especially  the  lavas,  also  vary  much  in  porosity.  The  meta- 
morphosed equivalent's  of  either  sedimentary  or  igneous  rocks 
may  differ  in  porosity.  The  contact  of  rocks  frequently  fur- 
nishes trunk-channels  for  underground  circulation.  Bedding 
partings  produced  by  shearing  stresses  during  deformation  fur- 
nish sheet  channels  parallel  to  the  strata,  or  openings  on  the 
anticlines  or  synclines.  Some  strata  when  deformed  may 
yield  by  fracture,  furnishing  channels  for  water-circulation, 
while  interlaminated  strata  may  yield  by  flowage,  thus  remain- 
ing relatively  impervious.  These  various  irregularities  may 
combine  in  different  ways. 

All  irregularities  in  porosity  and  structure  may  modify,  and 
in  many  cases  profoundly,  the  simple  general  statements  of  the 
present  paper  (pp.  309-317, 334-339)  concerning  the  character  of 
underground  circulation  and  the  concentration  of  ore-deposits. 
At  some  future  time  it  may  be  possible  to  divide  the  modifica- 
tions of  the  general  circulation  due  to  variation  of  porosity  and 
structure  into  classes,  but  for  the  present  this  cannot  be  done. 
The  modifications  of  the  general  circulation  which  occur  in 
many  individual  districts  must  first  be  studied  and  described, 
after  which  generalizations  may  possibly  be  made.  However, 
some  general  statements  may  be  made  in  reference  to  certain 
modifications  of  the  general  underground  circulation. 

The  Complexity  of  Openings. — In  the  general  discussion  an 
ore-deposit  has  been  spoken  of  as  if  it  were  a  single  continuous 
mass  formed  in  a  large  opening.  It  is  clear  this  is  not  the  fact, 
but,  on  the  contrary,  that  many  ore-deposits  have  very  complex 
forms.  An  ore-deposit  in  a  single  large  opening  is  exceptional. 
From  large  single  openings  to  openings  of  an  extraordinarily 
complex  character,  there  are  all  gradations.  A  trunk-channel 
of  circulation  may  be  a  set  of  distributive  faults ;  it  may  be  a 
group  of  parallel  or  intersecting  sets  of  openings  along  joints; 
it  may  be  the  minute  parallel  openings  of  fissility ;  it  may  be  a 
group  of  openings  along  bedding  planes  ;  it  may  be  the  shrink- 
age openings  formed  within  or  along  the  borders  of  cooling 
magma;  it  may  be  the  openings  in  an  autoclastic  rock  or 
reibungs-breccia  along  a  fissure ;  it  may  be  the  multitude  of 
openings  of  a  sandstone  or  a  conglomerate. 

Consequent  upon  the  many  irregularities,  trunk-channels  of 


SOME   PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       395 

circulation  may  vary  from  vertical  to  nearly  horizontal  atti- 
tudes. But  ore-deposits  ordinarily  have  important  vertical  com- 
ponents, although  they  may  be  found  in  nearly  horizontal  po- 
sitions. In  such  cases  the  trunk-channels  forming  the  deposits 
had  probably  vertical  components  somewhere  else. 

It  is  hardly  necessary  to  give  illustrations  of  ore-deposits  for 
each  of  these  complex  conditions.  However,  as  very  excellent 
illustrations  of  veins  of  a  very  composite  character  may  be 
mentioned  the  Cripple  Creek  deposits*  and  the  gold-quartz 
veins  of  Nevada  City  and  Grass  Valley,  California. f  The 
essential  point,  so  far  as  the  discussion  of  the  foregoing  pages 
is  concerned,  is  that  ore-deposits  commonly  occur  at  places 
where  there  are  trunk-channels  for  ascending  or  descending 
waters,  or  both.  In  order  that  metalliferous  material  shall 
be  brought  to  a  place  and  deposited  in  large  quantity,  there 
must  be  long-continued  circulation.  It  matters  not  whether  a 
trunk-channel  is  a  single  passage  or  is  composed  of  an  indefi- 
nite number  of  minor  passages,  the  principles  given  on  the 
previous  pages  are  applicable  to  the  deposition  of  ores  in  such 
trunk-channels. 

In  various  regions  the  conditions  are  so  exceedingly  com- 
plex that  ore-deposits  close  together  may  differ  from  one  another 
greatly.  This  is  the  best  evidence  that,  notwithstanding  their 
contiguity,  the  underground  trees  of  water  circulation  have 
been,  if  not  independent,  at  least  partly  so. 

This  is  well  illustrated  by  the  ore-deposits  of  Butte,  Montana. 
Here,  apparently,  the  metallic  contents  of  the  individual  feed- 
ing streams  and  even  the  trunk-channels  are  very  different 
within  short  distances.  At  this  place  are  two  main  zones  of 
mineralization.  The  more  important  product  of  one  of  these 
mineral  zones  is  silver  sulphide,  which  is  associated  with 
sulphides  of  lead,  zinc  and  iron,  and  with  silicate  of  manga- 
nese. The  chief  product  of  the  other  mineral  zone  is  copper, 
but  this  copper  carries  silver  in  important  amounts.  J 

*  "Mining  Geology  of  the  Cripple  Creek  District,"  by  E.  A.  F.  Penrose,  Jr., 
IQlh  Ann.  Kept.  U.  S.  Geol.  Surv.,  pt.  ii.,  1894-95. 

f  "The  Gold-Quartz  Veins  of  Nevada  City  and  Grass  Valley,  California,"  by 
"Waldemar  Lindgren,  VI ih  Ann.  Kept.  U.  S.  Geol.  Surv.,  pt.  ii.,  1895-96,  pp.  158- 
160,  259. 

t  "  Notes  on  the  Geology  of  Butte,  Montana,"  by  S.  P.  Emmons,  Trans.,  xvi., 
54,  1888. 


396      SOME   PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

Impervious  Strata  at  Various  Depths. — Slichter's  theoretical 
investigations  on  the  motions  of  groundwaters  show  that,  in 
order  to  discuss  the  flowage  under  any  given  set  of  conditions, 
it  must  be  assumed  that  the  flowage  is  limited  only  by  an  im- 
pervious stratum.*  It  is,  of  course,  understood  that  there  is 
no  such  thing  in  nature  as  an  absolutely  impervious  stratum, 
but  there  are  many  strata  which. are  practically  impervious. 
Wherever  there  is  an  impervious  stratum  in  a  district,  this  must 
be  counted  as  the  limit  of  circulation  in  that  direction.  The 
impervious  stratum  may  be  a  plastic  shale  which  yields  to  de- 
formation without  fracture ;  it  may  be  a  rock  intruded  after 
deformation  has  occurred,  thus  making  a  barrier.  If  an  im- 
pervious stratum  exists  at  a  given  depth,  the  effective  under- 
ground circulation  for  that  district  is  there  limited  or  divided, 
whether  the  stratum  be  at  the  depth  of  100  or  1000  or  more 
meters.  Of  course  there  will  be  all  gradations,  from  practically 
impervious  strata  to  strata  which  merely  check  the  circulation. 
It  is  believed  that  in  the  average  case  the  limit  of  effective  cir- 
culation is  probably  much  less  than  the  theoretical  limit  of 
10,000  meters  given  by  the  depth  of  the  zone  of  fracture. 

However,  if  an  impervious  stratum  be  but  100  meters  from 
the  surface  and  fissures  be  limited  to  that  depth  or  interrupted, 
the  laws  given  pp.  309— 31 7  will  commonly  apply  to  the  circulation 
above  the  stratum.  Therefore  such  a  fissure  may  be  occupied  by 
ascending  water  in  the  lower  part  and  by  descending  water  in  its 
upper  part.  Hence  an  ore-deposit  contained  in  such  a  shallow 
fissure  may  be  the  result  of  a  single  concentration  by  ascending 
or  descending  waters,  or  of  two  concentrations,  the  first  by 
ascending  and  the  second  by  descending  waters. 

The  foregoing  statement  in  reference  to  the  practical  limits 
of  underground  circulation  for  the  ore-deposits  of  a  given  dis- 
trict may  be  true  even  if  below  the  impervious  stratum  there 
are  other  strata,  fed  from  a  distance,  in  which  circulation  is 
occurring. 

Such  lower  pervious  strata  may  have  circulations  of  their 
own  independent  of  the  higher  circulations,  and  this  circulation 
may  produce  ore-bodies.  This  is  beautifully  illustrated  by  the 
Enterprise  mine  of  Rico,  Colo,  (see  Fig.  9,  p.  409),  described  by 

*  "Theoretical  Investigation  of  the  Motion  of  Ground  Waters,"  by  C.  S. 
Slichter,  19^  Ann.  Rept.  U.  S.  Geol.  Surv.  for  1897-98,  pt.  ii.,  pp.  329-357,  1899. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       397 

Rickard,*  in  which  the  ore  is  confined  to  fissured  and  broken 
limestones  and  sandstones  below  a  black  shale,  which  when 
bent  did  not  fracture,  and  therefore  afforded  no  channels  for 
water  circulation. 

In  this  connection  it  may  be  well  to  mention  the  Mercur 
district  of  Utah  (see  p.  411),  where  a  silver  ledge  and  a  gold 
ledge  about  100  feet  apart  each  occur  in  limestone  below  a  shale- 
like  stratum  of  altered  porphyry.  Spurr  regards  the  silver  ledge 
as  produced  by  an  earlier  mineralizing  period,  and  the  gold 
ledge  as  resulting  from  a  later  period  of  mineralization,  f  It 
may  be  suggested  that  the  true  explanation  of  the  existence  of 
two  mineral  ledges  so  near  together  and  of  such  different 
mineral  character  is  that  in  this  district  there  were  two  indepen- 
dent circulations  separated  by  impervious  strata,  the  upper  one, 
producing  the  gold  ledge,  being  between  the  two  impervious 
porphyry  belts,  while  the  lower  one,  forming  the  silver-deposit, 
was  below  the  lower  impervious  layer. 

That  a  difference  of  opinion  exists  as  to  the  source  and 
manner  of  deposition  of  the  lead  and  zinc  deposits  of  the  upper 
Mississippi  valley  has  already  been  mentioned.  (See  p.  364.) 
I  believe  that  these  deposits  furnish  an  instance  of  two  concen- 
trations where  an  impervious  stratum  limiting  the  concentrating 
circulation  was  at  a  very  moderate  depth. 

The  succession  for  this  district  in  descending  order,  accord- 
ing to  Chamberlin,J  is  as  follows  : 

Niagara  limestone,  137  meters  thick. 

Cincinnati  shale,  originally  61  meters  thick  (in  Iowa  called 
the  Maquoketa  shale).  § 

Galena  limestone,  bearing  organic  matter,  76  meters  thick. 

Trenton  limestone,  bearing  organic  matter,  12-30  meters 
thick,  with  mean  of  21  meters,  having  at  its  top  an  oil-bear- 
ing shale,  ||  "two  or  three  to  several  feet  in  thickness  at 


*  "The  Enterprise  Mine,  Eico,  Colo.,"  by  T.  A.  Eickard,  Trans.,  xxvi.,  1897, 
976-977  ;  also  Figs.  19,  36,  40. 

f  "Economic  Geology  of  the  Mercur  Mining  District,  Utah,"  by  J.  E.  Spurr, 
16th  Ann.  Rept.  U.  S.  Geol.  Survey,  pt.  ii.,  1894-5,  pp.  367-369. 

J  Chamberlin,  op.  cit.,  pp.  407-419. 

3  "Lead  and  Zinc  Deposits  of  Iowa,"  by  A.  G.  Leonard,  Iowa  Geol.  Survey, 
vol.  vi.,  1897,  p.  23. 

||  Blake,  Bull.  Geol.  Soc.  Am.,  vol.  v.,  pp.  28-29  ;  also  Trans.  Am.  Inst.  Min. 
Eng.,  vol.  xxii.,  pp.  629-632. 


398      SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

points,"*  and  containing  throughout  its  mass  various  shaly 
layers,  which,  however,  are  "  quite  decidedly  most  prevalent 
near  the  base  of  the  formation."f 

St.  Peter's  sandstone,  15—46  meters  thick. 

Lower  Magnesian  limestone,  30-76  meters  thick. 

Potsdam  sandstone,  213-244  meters  thick. 

Pre-Cambrian. 

It  is  to  be  noted  that  the  Galena  limestone  is  bounded  by 
impervious  shales  above  and  below,  and  that  the  same  statement 
applies  to  a  less  extent  in  reference  to  the  Trenton  limestone. 
As  to  the  impervious  character  of  the  thick  Cincinnati  shale 
above  the  Galena,  there  is  no  doubt.  One  might,  however, 
question  the  impervious  character  of  the  thin  bed  of  shale  at 
the  top  of  the  Trenton,  but  that  this  is  relatively  impervious  is 
strongly  indicated  by  the  fact  that  in  the  Shullsburg  and  other 
districts,  as  pointed  out  by  Blake,  the  ore-deposits  stop  at  the 
top  of  this  layer.  J  While  in  the  Trenton  the  impervious 
shales  are  more  prominent  at  the  top  and  near  the  bottom, 
there  are  more  or  less  impervious  layers  within  the  Trenton. 

The  strata  dip  to  the  southwest.  Chamberlin  says  for  Wis- 
consin, "  The  strata  on  the  north  side  of  the  lead  region  are 
500  feet  (152  meters)  higher  than  those  of  the  south  side, 
and  if  traced  farther  the  difference  in  altitude  would  be  found 
greater.  Beds  on  the  eastern  side  are  350  feet  (107  meters) 
higher  than  on  the  west  side."§  Superimposed  upon  the 
general  southwest  monocline  of  the  district  are  a  number  of 
subordinate  anticlines  and  synclines,  and  the  ores  are  mainly 
confined  to  the  synclines.  ||  At  the  time  of  this  deformation 
the  brittle  limestones  were  probably  fractured,  producing  the 
present  complex  system  of  intersecting  joints;  but  the  plastic 
shales  were  deformed  with  comparatively  little  fracturing.  The 
time  at  which  the  deformation  occurred  is  not  definitely  known, 
but  in  all  probability  it  antedated  the  deep  erosion  and  con- 
centration of  ores  in  the  district.^ 

*  Clamberlin,  cit.,  p.  412.      f  Chamberlin,  Geol.  of  Wis.,  vol.  iv.,  1882,  p.  409. 

J  "Lead  and  Zinc  Deposits  of  the  Mississippi  Valley,"  by  Win.  P.  Blake, 
Trans.  Am.  Inst.  Min.  Eng.,  vol.  xxii.,  1894,  pp.  629-632.  (Discussion  of  Jen- 
ney's  paper.) 

\  Chamberlin,  cit.,  p.  422.  ||  Chamberlin,  cit.,  pp.  432-438. 

ff  "Lead  and  Zinc  Deposits  of  the  Mississippi  Valley,"  by  W.  P.  Jenney, 
Trans.  Am.  Inst.  Min.  Eng.,  vol.  xxii.,  1894,  pp.  208-209.  Discussion  of  Jenney 's 
paper,  by  Wm.  P.  Blake,  op.  cit.,  pp.  628-629.  Chamberlin,  op.  cit.,  pp.  427,  485. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       399 

Areally  the  ores  occur  to  a  much  greater  extent  east  of  the 
Mississippi  river  than  west  of  it;  that  is,  mainly  east  of  the 
main  line  of  drainage.  As  to  horizons,  by  far  the  greater 
quantity  of  ores  which  have  yet  been  abstracted  were  found  in 
the  Galena  limestone.*  However,  considerable  quantities  of 
ores  have  been  taken  from  the  Trenton,  and  subordinate 
quantities  from  the  St.  Peters  and  Lower  Magnesian.  The  ores 
occur  in  the  Galena  from  the  top  to  the  bottom.  In  cases  where 
erosion  has  not  cut  deep  into  the  Trenton,  the  ore-deposits  are 
apt  to  be  found  near  the  overlying  Cincinnati  shale.  For  in- 
stance, in  Iowa,  where  the  shales  are  close  at  hand  as  a  contin- 
uous formation,  Leonardf  states  that  the  ore  occurs  "  mostly 
near  the  top  of  the  Galena  limestone,  within  the  upper  50  or 
60  feet  (15  meters  to  18  meters)."  Where  the  drainage  lines 
have  cut  through  the  Galena  into  the  Trenton  or  lower  forma- 
tions, the  ores  of  the  Galena  are  likely,  in  large  measure,  to  be 
near  the  bottom  of  the  formation,  and  considerable  bodies  may 
rest  upon  the  oil-rock  which  marks  the  beginning  of  the 
Trenton. 

Following  Chamberlin,  I  think  it  probable  that  a  large  part 
of  the  material  of  these  ores  was  once  disseminated  through 
the  sedimentary  rocks,  and  especially  the  limestones.  My  con- 
ception of  the  probable  process  of  concentration  in  the  Galena 
limestone  is  as  follows : 

While  in  the  Wisconsin  lead  district  the  Niagara  limestone 
and  Cincinnati  shale  are  only  found  on  occasional  mounds,  as 
pointed  out  by  Chamberlin,  J  there  is  no  question  but  that  these 
formations  once  extended  over  the  entire  district.  As  already 
noted,  the  Cincinnati  shale  is  a  very  impervious  stratum.  Un- 
til it  was  cut  through  by  the  drainage,  it  is  probable  that  eifec- 
tive  concentration  of  the  ores  did  not  begin.  When  it  was 
once  cut  by  erosion,  then  I  conceive  the  main  concentration 
history  of  the  ore-deposits  to  have  begun.  The  Mississippi 
river  and  areas  adjacent  were  the  places  where  the  drainage 
was  the  lowest.  However,  these  were  not  the  places  first  cut 
through  by  erosion,  for  the  difference  between  the  level  of 
the  Mississippi  drainage  and  the  tributaries  adjacent  is  not  so 

*  Geol.  of  Wis.,  vol.  iv.,  pp.  407,  457,  481. 

f  Leonard,  cit.,  pp.  43,  61. 

J  Chamberlin,  cit.t  pp.  410-412. 


400       SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

great  as  the  dip  of  the  strata  to  the  southwest.  In  all  proba- 
bility, therefore,  the  Cincinnati  was  first  cut  through,  and  the 
Galena  encroached  upon  by  erosion  north  and  east  of  the  lead 
and  zinc  district.  This  is  probable  from  the  fact  that  at  the 
present  time  the  Mississippi  river  for  the  most  part  in  the  lead 
district  is  on  the  Trenton,  and  never  reaches  deeper  than  the 
St.  Peters;  while  the  majority  of  the  smaller  streams  in  the 
northeastern  part  of  the  lead  district  have  cut  into  the  St. 
Peters,  and  the  headwaters  of  some  of  them,  notably  the  Pec- 
atonica,  Platte,  the  Grant  river,  have  cut  through  the  St.  Peters 
into  the  Magnesian ;  while  still  farther  to  the  northeast,  north 
of  the  divide,  occupied  by  the  Lancaster  branch  of  the  C.  &  N". 
W.  By.,  the  strong  Wisconsin  has  cut  down  to  the  Cambrian.* 

It  is  to  be  remembered  that  the  pervious  strata  overlain  by 
impervious  strata  along  the  Mississippi  river  bear  water  under 
pressure,  as  is  shown  by  numerous  artesian  wells.  The  feeding 
area  is  the  higher  ground  to  the  northeast.  It  is  highly  prob- 
able that  the  broken  brittle  Galena  limestone  was  a  formation 
which  was  capable  of  carrying  water  to  considerable  distances, 
and  in  considerable  quantities,  although  probably  not  compar- 
able in  these  respects  to  the  St.  Peters  or  Potsdam  sandstones. 
The  lead  and  zinc  district  of  Wisconsin  is  wholly  south  of  the 
'divide  between  the  Wisconsin  river  and  the  tributaries  of  the 
Mississippi.  When  the  Wisconsin  drainage  north  of  the  divide 
had  cut  through  the  Cincinnati  shale,  this  furnished  a  feed- 
ing area  to  the  Galena  limestone.  When  later  the  Mississippi 
tributaries  south  of  the  divide  had  cut  through  the  Cincinnati 
shale  into  the  Galena,  the  waters  entering  north  of  the  divide 
escaped. 

As  erosion  continued,  the  area  in  which  the  Cincinnati  was 
cut  through  and  the  Galena  penetrated,  gradually  extended  to 
the  southwest  until  the  Mississippi  itself  had  cut  through  the 
Cincinnati.  During  this  time  the  water  entered  the  Galena 
limestone  at  the  higher  elevations,  that  is,  to  the  north  and 
east,  followed  along  this  formation,  and  escaped  at  some  lower 
point  toward  the  Mississippi  river.  While  the  water  to  the 
greatest  extent  followed  the  upper  portion  of  the  Galena,  it  is 
believed  that  this  broken  formation  was  searched  to  its  deepest 

*  See  "Atlas  of  Wisconsin,''  pis.  i.  and  viii. 


SOME    PltlNCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       401 

part  according  to  the  laws  of  flowagc  given  pp.  309-317.  The 
places  of  escape  were  near  the  top  of  the  formation,  and,  there- 
fore, the  waters  of  the  trunk-channels  leading  to  these  places 
were  ascending. 

As  erosion  slowly  progressed,  the  zone  of  rising  waters  and 
escape  slowly  migrated  from  the  northeastern  part  of  the  lead 
and  zinc  district  to  the  southwestern  part.  The  nature  of  the 
circulation  at  a  given  time  is  roughly  represented  by  Fig.  7,  a 
northeast-southwest  vertical  section.  The  surface  of  the  country 


Ideal  Vertical  Section  of  the  Flow  of  Underground  Water  in  the  Galena  Lime- 
stone of  the  Upper  Mississippi  Valley. 

is  shown  by  A,  A',  A",  in  which  A,  A'  is  the  cross-section  of  a 
northwest  and  southeast  belt,  where  waters  enter,  and  A"  is  in  a 
parallel  belt  to  the  southwest,  in  which  the  waters  escape.  The 
numerous  curved  lines  below  the  Cincinnati  shale  are  intended 
to  represent  the  circulation.  The  downward-moving  lateral- 
moving  waters,  in  the  early  stages  of  their  journey,  were  oxidiz- 
ing and  dissolving  waters.  When,  through  the  organic  matter 
contained  in  the  formation,  the  oxygen  had  been  exhausted  and 
the  oxidized  products  reduced,  the  waters  were  sulphuretted 


402       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

waters,  as  explained  pp.  348—350.  The  upward-moving  waters  in 
the  trunk-channels  (A"  B')  were  precipitating  waters,  as  ex- 
plained pp.  337-338.  And  especially  the  material  was  likely  to 
be  precipitated  where  the  waters  came  in  contact  with  ahundant 
organic  material. 

Where  the  limestone  itself  contained  many  carbonaceous 
substances,  the  material  precipitated  might  have  been  widely 
disseminated;  but  as  the  carbonaceous  material  was  more  abun- 
dant in  the  clay  layers,  which,  to  some  extent  at  least,  repre- 
sented places  where  clay  openings  and  ore-deposits  now  exist, 
the  ore  material  was  still  more  largely  precipitated.  The  trans- 
fers of  ore  material  at  this  time  were,  indeed,  exceedingly 
complex,  but  because  of  a  combination  of  all  of  the  factors 
considered  in  the  general  part  of  this  paper,  the  material  was 
precipitated  to  a  greater  degree  in  the  trunk-channels  where  the 
water  was  ascending  than  anywhere  else. 

In  an  early  stage  of  the  process  the  first  concentration  by 
ascending  waters  took  place  in  the  northeastern  part  of  the 
district.  By  the  time  that  erosion  had  cut  through  the  Cin- 
cinnati into  the  Galena  in  the  southwestern  part  of  the  district, 
and  ascending  waters  were  concentrating  ores,  the  northeastern 
part  of  the  district  might  have  been  a  feeding  area  where  waters 
were  descending,  and  a  second  concentration  taking  place. 
Therefore,  the  second  concentration  by  descending  waters  was 
going  on  in  the  northeastern  part  of  the  district  at  the  same 
time  that  the  first  concentration  by  ascending  waters  was  oc- 
curring to  the  southwest.  At  the  present  time  the  erosion  has 
cut  sufficiently  deep  so  that  the  second  concentration  by  down- 
ward-moving waters  has  extended  quite  to  the  Mississippi  river, 
and,  indeed,  to  the  west  of  it.  At  the  present  time  the  condi- 
tion of  affairs,  except  the  circulation,  is  represented  by  Fig.  7 
below  the  line  B  B',  which  may  be  taken  as  the  present  surface 
of  erosion. 

This  general  statement  as  to  the  order  of  events  concerning 
the  district  as  a  whole  would  also  apply  to  the  local  anticlines 
and  synclines.  Other  things  being  equal,  where  there  were  an- 
ticlines there  erosion  would  first  cut  through  the  Cincinnati 
shale,  and  water  make  its  way  into  the  Galena  formation.  Later, 
when  erosion  had  cut  deep  enough  to  expose  the  bottoms  of  the 
adjacent  synclines,  there  the  water  entering  at  the  anticlines 
arose  and  escaped,  and  a  first  concentration  occurred  in  the 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       403 

synclinal  areas.  Later,  when  erosion  had  cut  deeper,  a  second 
concentration  by  descending  waters  occurred ;  and  thus  these 
concentrations  were  localized  in  the  synclines,  where,  accord- 
ing to  Chamberlin,  they  now  occur.  In  this  connection  it  is 
to  be  remembered  that  the  anticlines  and  synclines  of  the  dis- 
trict are  very  gentle.  Therefore,  the  conditions  are  here  differ- 
ent from  those  of  a  district  where  there  are  sharp,  strongly 
pitching  folds  covered  by  impervious  strata.  (See  pp.  405-412.) 

My  conception  of  the  process  of  concentration  of  ores  in  the 
Galena  limestones  is,  therefore,  that  of  a  circulation  practically 
limited  above  by  the  Cincinnati  shale  and  largely  limited  below 
by  the  impervious  oil  shale  of  the  Trenton.  To  what  extent 
ascending  waters  from  the  St.  Peters,  Cambrian  and  pre-Cam- 
brian  rocks  under  the  pressure  of  considerable  head  were  able 
to  work  up  through  the  more  or  less  impervious  shales  of  the 
Trenton  limestone  is  uncertain.  For  the  purposes  of  this  paper 
it  makes  little  difference  whether  during  the  time  of  deposition 
of  ores  in  the  Galena  limestones  by  ascending  waters  the  cir- 
culation was  practically  limited  by  the  Cincinnati  shale  above 
and  the  Trenton  below,  or  whether  a  contribution  of  waters 
ascended  from  greater  depths.  For  a  given  point  where  the 
Cincinnati  shale  had  just  been  removed,  the  first  concentration 
occurred  by  ascending  waters,  and  later  when  the  Cincinnati 
shale  had  been  removed  farther  to  the  southwest  the  second 
concentration  by  descending  waters  took  place.  The  belt  of 
second  concentrates  by  descending  waters  slowly  migrated 
downward  as  erosion  extended  into  the  Galena.  Where  the 
denudation  has  gone  a  little  way  into  the  Galena,  the  ore-de- 
posits are  found  near  its  upper  part.  Where  denudation  has 
gone  well  down  into  the  Galena,  the  ore-deposits  are  found  near 
its  lower  part.  Where  the  lines  of  drainage  are  considerably 
below  the  Galena  the  second  concentration  and  downward  mi- 
gration of  the  ores  has  resulted  in  the  formation  of  consider- 
able deposits  directly  upon  the  petroleum  oil-rock  at  the  top  of 
the  Trenton.  In  these  cases  the  materials  exploited  are  prob- 
ably the  second  concentrates  from  the  entire  Galena  formation. 

The  precipitation  of  the  lead-  and  zinc-ores  by  reactions  of 
the  oxidized  products  upon  the  remaining  sulphides,  and  by  the 
reducing  action  of  the  organic  material  contained  in  the  rock 
and  the  organic  material  coming  down  from  above,  have  already 
been  considered.  (See  pp.  360-364.)  However,  in  this  connec- 


404       SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

tion  it  should  be  noted  that  the  position  of  the  ores  upon  the 
oil-rock  is  probably  explained  through  the  reducing  action  of 
solutions  slowly  oozing  up  through  the  shale  ;  for  the  ore  is  not 
mainly  precipitated  in  the  oil-rock,  but  immediately  above  it. 
In  this  connection  it  is  to  be  remembered  that  all  of  the  per- 
vious strata  capped  by  impervious  strata  in  this  region  bear 
waters  under  pressure.  Therefore,  water  would  slowly  pass 
up  through  the  shale,  for  no  formation  is  absolutely  impervious. 

It  will  be  seen  at  once  that  the  above  theory  of  circulation 
explains  the  formation  of  rich  deposits  near  the  top  of  the  Ga- 
lena, as  in  Iowa,  and  these  deposits  are  very  difficult  to  account 
for  solely  upon  the  theory  of  descending  waters.  It  accounts 
equally  well  for  the  formation  of  rich  ores  in  the  middle  and 
lower  horizons  of  the  Galena  where  denudation  has  gone  fur- 
ther. It  accounts  for  the  much  wider  distribution  of  the  ores 
east  of  the  Mississippi  river  than  west  of  the  Mississippi  river, 
since  the  strata  west  of  the  Mississippi  river  continue  to  dip  to 
the  southwest ;  and  the  drainage  west  of  the  river  has  cut  only 
for  a  little  way  deep  enough  so  that  the  process  of  concentra- 
tion as  above  outlined  could  occur. 

In  the  parts  of  the  Upper  Mississippi  valley  district  where 
erosion  has  cut  deeply  into  the  Trenton,  and  especially  where 
it  has  gone  into  the  St.  Peters,  a  similar  history  is  applicable  to 
the  Trenton  formation ;  only  the  Trenton  is  more  variable  in 
its  porosity  than  the  Galena,  and  the  deposits  may  not  have 
been  wholly  derived  from  the  Trenton  formation,  but  may  have 
received  a  subordinate  contribution  from  the  Galena  formation 
which  has  been  removed  by  erosion  in  part  or  altogether. 

In  the  application  of  the  foregoing  it  is,  of  course,  understood 
that  the  action  of  ascending  and  descending  waters  in  a  given 
fissure  is  not  wholly  successive ;  but .  is  in  large  measure  si- 
multaneous. In  the  early  stages  of  the  deposition  of  an  ore- 
deposit  in  a  given  fissure,  ascending  water  would  be  likely  to 
be  the  dominant  factor ;  in  an  intermediate  stage  both  ascend- 
ing and  descending  waters  would  be  at  work ;  and  in  the  later 
stages  of  the  process,  and  at  the  present  time,  descending  waters 
are  the  dominant,  and,  perhaps,  in  the  cases  of  many  of  the 
deposits  where  the  oil-rock  of  the  Trenton  is  near  the  surface, 
almost  the  sole  factor. 

At  the  bottoms  of  valleys  the  waters  have  continued  to  be 


SOME   PRINCIPLES    CONTROLLING   DEPOSITION   OF    ORES.      405 

essentially  ascending  instead  of  descending  to  the  present  time. 
The  fact  of  their  present  ascension  Chamberlin*  notes.  Thus 
in  these  places  a  second  concentration  has  not  occurred,  and, 
therefore,  such  places  are  deficient  in  workable  ore-deposits,  as 
noted  by  Chamberlin.  f  (See  p.  418.) 

The  case  of  the  lead  and  zinc  district  has  been  dwelt  upon, 
as  it  seems  to  me  to  illustrate  almost  ideally  the  practical  lim- 
itations of  circulating  water  by  impervious  strata.  It  shows 
that  precisely  the  same  principles  of  ore  deposition  are  appli- 
cable when  the  limit  of  circulation  is  less  than  100  meters  deep 
that  apply  when  the  circulation  extends  to  the  very  bottom  of 
the  zone  of  fracture. 

If  my  views  be  compared  with  those  of  the  ascensionists, 
typified  by  Jenney,  and  the  descensionists,  typified  by  Cham- 
berlin, it  will  be  seen  that  I  occupy  an  intermediate  position. 
Upon  the  fundamental  point  as  to  whether  or  not  the  ores  are 
derived  from  a  deep-seated  source  or  are  derived  from  sedimen- 
tary rocks,  I  am  inclined  to  follow  Chamberlin,  although  I 
do  not  feel  certain  that  some  of  the  material  for  the  ores  were 
not  derived  from  a  deeper  source. 

The  account  given  pp.  357-364,  397—405,  in  reference  to  the 
ore-deposits  of  the  Upper  Mississippi  valley  is  not  even  approxi- 
mately complete.  To  give  a  satisfactory  account  of  the  genesis 
of  the  ore-deposits  of  this  district,  would  require  a  detailed  study 
and  a  monographic  report.  Such  a  report  upon  many  phases  of 
the  problem — a  remarkable  paper — has  already  been  written 
by  Chamberlin.  J  When  the  study  is  completed,  it  will  be 
possible  to  explain  not  only  the  general  order  of  mineral  succes- 
sion vertically,  but  the  multifarious  and  complex  distributions, 
such  as  the  cycles  of  depositions  already  mentioned. 

Pitching  Troughs  and  Arches. — Another  interesting  special  case 
of  influence  of  porosity  and  structure  is  that  where  alternately 
pervious  and  impervious  layers  are  in  a  set  of  pitching  folds.  The 
varying  porosity  may  follow  from  original  difference  in  the  por- 
osity of  the  layers,  or  it  may  result  from  the  deformation  itself. 
The  more  rigid  strata  may  be  deformed  by  fracture,  and  the  less 

*  Chamberlin,  op.  cit.,  p.  565. 
t  Chamberlin,  op.  cit.,  p.  563. 

£ . "  Ore-deposits  of  Southwestern  Wisconsin,"  by  T.  C.  Chamberlin,  Geol.  of 
Win.,  vol.  iv.,  1882,  pp.  365-571. 


406      SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

rigid  by  flowage.  Also,  the  convex  sides  of  the  brittle  layers 
are  likely  to  be  more  fractured,  and,  therefore,  more  porous 
than  the  concave  sides.  This  would  place  the  more  porous 
parts  of  a  stratum  in  contact  with  the  confining  impervious 
stratum  below  at  the  synclines  and  above  at  the  anticlines. 
Furthermore,  where  the  strata  are  closely  folded,  unless  there 
is  very  great  distortion  of  the  strata,  openings  will  form 
between  the  layers  at  the  synclines  and  anticlines,  thus  furnish- 
ing trunk-channels. 

Any  combinations  of  porous  layers  with  impervious  layers  in 
folds  are  likely  to  give  trunk-channels  for  underground  water 
at  the  troughs  above  impervious  strata,  and  at  the  crests  below 
impervious  strata.  "When  descending  waters  come  into  contact 
with  an  impervious  stratum,  they  are  deflected  toward  the  syn- 
clines, and  there  finding  the  trunk-channels,  they  follow  the 
troughs  downward  along  the  pitch.  When  ascending  waters 
come  into  contact  with  an  impervious  stratum,  they  are  deflected 
toward  the  anticlines,  and  there  finding  the  trunk-channels,  fol- 
low the  arches  upward  along  the  pitch.  Therefore,  ore-deposits 
produced  by  descending  waters  are  often  found  in  pitching 
troughs  underlain  by  relatively  impervious  strata ;  and  ore-de- 
posits produced  by  ascending  waters  are  rather  frequently  found 
in  pitching  arches  overlain  by  impervious  strata. 

The  Lake  Superior  iron-ores  furnish  an  admirable  illustration 
of  the  concentration  of  ores  by  descending  waters  in  pitching 
troughs  which  are  on  impervious  basements.  Since  these  ore- 
deposits,  which  fully  illustrate  the  principles  of  concentration 
of  ores  by  descending  water  in  pitching  impervious  troughs, 
are  fully  discussed  elsewhere,  ores  of  this  class  will  not  be  here 
further  considered. 

A  case  in  which  ore  is  probably  deposited  by  ascending 
waters  in  arches,  because  there  concentrated  by  impervious  roofs, 
is  furnished  by  the  Bendigo  gold-district  of  Australia.*  The 
typical  position  for  the  gold  in  the  district,  according  to  Bickard, 
is  immediately  below  a  slate,  on  top  of  a  sandstone.  The  slate  is 
the  impervious  stratum  and  the  sandstone  the  pervious  stratum. 
The  ores  are,  presumably,  in  part,  in  the  openings  between  the 


*  "The  Bendigo  Gold-Field,"  by  T.  A.  Kickard,  Trans.,  xx.,  1892,  pp.  463- 
645. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.      407 

layers  made  by  folding.*  (Fig.  8.)  Moreover,  in  this  district 
there  are  a  large  number  of  alternations  of  pervious  and  imper- 
vious strata,  as  a  result  of  which  a  number  of  concentrations  have 
occurred  one  above  the  other.  While  Bickard  does  not  speci- 
fically speak  of  the  pitch  of  the  anticlines,  the  longitudinal 
sections  show  that  they  do  have  a  marked  pitch.  Rickard's 
explanation  of  the  location  of  the  oresf  is  that  the  apices  of  the 
anticlines  would  furnish  more  open  passages  than  the  synclines, 

FIG.  8. 


w/Mm..    x 

SI 


|S.U<TE  fry-XV^I  QUARTZ 

SADDLE. 

The  Concentration  of  Ore  by  Ascending  Water  at  a  Crest  below  an  Impervious 
Stratum.     After  Eickard  (Trans.,  xx.,  467,  Fig.  2). 

but  why  at  a  given  level  this  would  be  so  does  not  appear. 
This  explanation  may  possibly  be  to  some  extent  applicable,  but 
the  pitching  arches  concentrating  the  ascending  solutions  below 
impervious  strata  are  believed  to  be  the  main  cause  of  the  local- 
ization of  the  gold. 

Another  excellent  illustration  of  ore-solutions  concentrated 
by  an  impervious  roof  is  furnished  by  the  Mercur  district,  Utah, 
described  by  Spurr,{  where  two  ore-bearing  beds,  one  called 
the  silver  ledge  and  the  other  called  the  gold  ledge,  about  100 

*  Eickard,  loc.  cit. ,  Fig.  2,  p.  467.  See  also  Fig.  12,  p.  481 ;  Fig  13,  p.  483  ; 
Fig.  37,  p.  499  ;  and  Fig.  38,  p.  501. 

t  "The  Origin  of  the  Gold-Bearing  Quartz  of  the  Bendigo  Eeefs,"  by  T.  A. 
Eickard,  Trans. ,  xxii. ,  p.  319. 

J  "Economic  Geology  of  the  Mercur  Mining  District,  Utah,"  by  J.  E.  Spurr, 
16th  Ann.  Rept.  U.  S.  Geol.  Surv.,  pt.  ii.,  1894-95,  pp.  365-7,  395,  399-401,  449, 
454  ;  see  also  PL  xxxiv. ,  Figs.  44  and  45,  and  PI.  xxv. ,  p.  360. 


408       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

feet  apart,  occur  in  a  limestone  below  seams  or  beds  of  shale-like 
material,  which,  however,  is  very  much  altered  porphyry.  The 
ores  are  especially  localized  where  fissures  reach  these  beds, 
and  thus  displace  them,  and  in  some  cases  form  local  arches, 
although  Spurr  does  not  mention  this  latter  fact.  Moreover, 
the  entire  ore  district  is  located  upon  a  general  anticline, 
furnishing  a  general  pitching  arch. 

Another  exceedingly  interesting  illustration  of  the  depo- 
sition of  ores  below  an  impervious  stratum  in  pitching  arches 
is  that  furnished  by  the  Enterprise  mine  of  Rico,  Colorado,  de- 
scribed by  Rickard  in  a  paper  already  cited.*  In  this  district 
above  the  ore-bodies  is  an  impervious  shale  which  is  not  broken 
at  all,  or  very  rarely,  by  the  fissures.  The  ore  occurs  in  two 
places,  (1)  in  nearly  vertical  fissures  extending  indefinitely  down- 
ward below  the  shale,  but  not  upward  into  it.  The  verticals 
are  cut  by  cross-fissures,  and  where  the  intersections  occur  the 
fissures  are  likely  to  be  unusually  rich.  (See  pp.  340-343.)  (2) 
The  larger  masses  of  ore  are  found  in  crushed  or  fractured  lime- 
stone below  the  black  shale  and  above  the  fissures.  More- 
over, these  bodies  are  narrow  laterally,  and  are  parallel  to  the 
strike  of  the  verticals  and  also  of  the  cross-veins.  Figs.  9  and 
10  show  that  they  occur  below  anticlinal  flexures  of  the  shale 
made  by  the  deformation  resulting  in  the  faulting  in  the  more 
brittle  rocks  below.  Rlckard  regards  the  deposits  as  the  result 
of  ascending  waters,  since  the  fissures  continue  downward  but 
do  not  extend  upward  into  the  shale.  It  is  believed  that  when 
the  Enterprise  deposit  is  further  studied  it  will  be  found  that 
the  flexures  of  the  shale  furnishing  the  anticlinal  arches  have 
a  pitch  (and  indeed  this  is  indicated  by  Fig.  10),  and  that  the 
waters  issuing  from  the  verticals  and  the  cross-fissures  followed 
these  arches  upward  until  the  pitch  somewhere  brought  them 
to  the  surface,  at  which  places  the  waters  escaped  as  springs ;  for 
the  waters  of  the  ascending  circulation  must  have  somewhere 
escaped,  and  that  they  could  not  do  through  the  impervious 
shale. 

At  this  point  it  may  be  suggested  that  where  ore-deposits 
occur  in  connection  with  pitching  anticlines  and  synclines,  that 
their  positions  furnish  a  criterion  by  which  it  may  be  decided 

*  "The  Enterprise  Mine,  Kico,  Colo.,"  by  T.  A.  Kickard,  Trans.,  xxvi.,  p.  906, 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       409 

whether  their  first  concentration  was  accomplished  by  ascend- 
ing or  by  descending  waters.  Where  the  ores  occur  in  pitching 
arches  bounded  above  by  impervious  strata,  the  presumption  is 
that  they  were  concentrated  by  ascending  waters ;  where  the 
ore-deposits  occur  in  pitching  troughs  bottomed  by  impervious 

FIG.  9. 


Black  finely  laminated  Shale 


Ore 


v--/ 


JUMBO  No.  2.  VEIN  AT  THE  CONTACT 

Ore  below  a  Gentle  Arch  of  Impervious  Shale,  where  the  Feeding  Fissure  Com- 
ing from  Below  Ends  at  the  Bottom  of  the  Impervious  Layer.  After  Kickard 
(Trans.,  xxvi.,  961,  Fig.  36). 

strata,  the  inference  is  that  they  were  concentrated  by  descend- 
ing waters;  for,  as  already  explained,  it  is  difficult  to  see  how 
waters  can  be  converged  at  such  positions  by  moving  in  the  re- 
verse directions.  Of  course,  this  criterion  cannot  be  too  rigidly 
applied,  for  independently  of  the  impervious  strata,  openings 
which  so  frequently  occur  on  anticlines  and  synclines  might 


410      SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

furnish  trunk-channels  which  could  be  taken  advantage  of  by 
ascending  or   descending  waters.     Thus  in  the  Bendigo  gold 


district  of  Australia,  while  the  more  important  ore-deposits  are 
in  anticlines,  occasionally  an  ore-deposit  is  found  on  a  syncline.* 

*  "The  Bendigo  Gold-Field,"  by  T.  A.  Kickard.     Trans.,  xx.,  1892,  p.  484. 
See  Fig.  6,  p.  475. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       411 

If  the  above  criterion  be  applied  to  the  Leadville  ore-deposits, 
the  conclusion  would  be  that  the  sulphides  of  Leadville  were 
deposited  by  ascending  waters,  since  they  mainly  occur  on  an- 
ticlines or  anticlinoria  below  a  relatively  impervious  porphyry 
and  in  a  much-broken  limestone,  mainly  the  blue  limestone.* 
The  plates  of  the  Emmons  atlas  show  that  the  ore  more  largely 
occurs  on  anticlines  and  on  the  flanks  of  the  folds  than  in  syn- 
clines,  although  some  subordinate  synclines  on  anticlinoria  con- 
tain ore-bodies.  When  deposited  as  sulphides  the  ores  were 
probably  somewhat  more  uniformly  distributed  than  at  present 
along  the  base  of  the  porphyries.  Later,  when  the  second  con- 
centration occurred  by  downward-moving  waters,  the  material 
which  in  many  places  was  on  denuded  anticlines  was  in  part 
carried  down  the  limbs  of  the  folds  under  the  porphyry  into  the 
limestone.  At  this  time  doubtless,  also,  the  limestone  would 
be  largely  dissolved  and  the  materials  would  be  carried  not 
only  down  along  the  dip  but  across  the  beds,  thus  producing 
the  very  great  irregularities  which  are  characteristic  of  the  bot- 
toms of  these  deposits.  If  the  above  explanation  be  correct, 
the  Leadville  ores  would  present  another  case  in  which  both 
the  ascensionists  and  descensionists  have  had  a  part  of  the 
truth,  f 

In  this  connection  it  may  be  suggested  that  the  positions  of 
the  ores  in  reference  to  the  limestone  and  porphyry  in  the 
Leadville  district  are  remarkably  similar  to  those  of  the  ores  in 
^he  Mercur  district  in  reference  to  almost  identical  formations. 
The  forms  of  the  deposits,  their  irregular  under-surface  in  the 
limestone,  and  the  regular  surface  at  the  porphyry  are  all  iden- 
tical. Both  Emmons  and  Spurr  agree  that  the  ore  in  the  Mer- 
cur district  was  deposited  as  sulphides  by  ascending  waters. 
If  this  be  true,  the  same  explanation  is  probably  applicable  to 
the  Leadville  district. 

A  pervious  layer  or  other  opening  furnishing  a  trunk- 
channel  for  circulating  waters  may  be  bounded  on  both  sides 
by  impervious  strata.  In  this  case  the  ore-deposit  may  be  pro- 
duced by  ascending  or  descending  waters.  But  where  the  strata 

*  "  Geology  and  Mining  Industry  of  Leadville,"  by  S.  F.  Emmons,  Mon.  U.  S. 
Geol.  Surv.,  No.  12,  1886,  chap,  vi.,  pp.  539-584. 

f  "Geology  and  Ore-Deposits  of  IroD  Hill,  Col.,"  by  A.  A.  Blow,  Trans., 
xviii.,  1890,  180. 


412       SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

are  folded  into  pitching  anticlines  and  synclines,  the  positions 
of  the  ores  with  reference  to  the  folds  would  determine  whether 
the  precipitating  waters  were  ascending  or  descending.  An 
excellent  illustration  of  ore-deposits  at  the  openings  of  anticlines 
between  relatively  impervious  strata,  presumably  formed  by 
ascending  waters,  are  the  gold-bearing  quartz-ores  in  the  slates 
and  quartzites  of  Nova  Scotia,  described  by  Faribault.*  Here 
there  are  a  great  many  parallel  deposits  directly  at  the  anti- 
clines or  on  some  parts  of  the  anticlinal  folds,  the  deposits 
being  separated  by  layers  of  relatively  impervious  slate.  Fur- 
thermore, the  largest  deposits  are  located  on  the  great  pitching 
anticlines  rather  than  the  subordinate  ones. 

Porous  pitching  troughs  below  an  impervious  stratum  or 
above  an  impervious  stratum  or  between  impervious  strata  may 
have  a  different  origin  from  those  mentioned.  Very  frequently 
such  troughs  are  produced  in  part  or  in  whole  by  intrusive 
igneous  rocks.  For  instance,  if  sedimentary  strata  have  a 
monoclinal  dip  and  a  dike  cuts  across  the  strata,  a  pitching 
trough  may  be  produced,  as,  for  instance,  in  the  Penokee 
district,  f  An  intruded  igneous  rock  may  follow  the  contact 
between  folded  strata,  and  thus  furnish  a  trough  or  arch 
bounded  by  an  impervious  formation.  Various  other  ways 
will  immediately  occur  to  one  in  which  pitching  troughs  or 
arches  with  impervious  basements  or  roofs  or  both,  may  be 
produced.  It  matters  not  how  the  trough  or  arch  be  produced, 
provided  a  porous  stratum  or  an  opening  between  the  layers 
furnish  a  trunk-channel,  such  a  trough  or  arch  will  be  favor- 
able for  the  concentration  of  ores.  Of  course,  other  favorable 
conditions  must  co-operate  with  these  in  order  to  produce  an 
ore-deposit. 

Combinations  of  pervious  and  impervious  strata,  united  with 
joints,  faults  and  other  structures  which  affect  some  impervious 
strata  and  do  not  others,  may  furnish  extraordinarily  complex 
sets  of  conditions  which  I  am  not  able  to  discuss  in  a  general 
way ;  but  such  will  undoubtedly  yield  interesting  results  when 
studied  in  special  cases. 

*  "The  Gold  Measures  of  Nova  Scotia  and  Deep  Mining,"  by  E.  R  Fari- 
bault, Paper  read  before  the  Canadian  Mining  Institute,  March,  1899.  Pub- 
lished by  the  Mining  Assoc.  of  Nova  Scotia,  1899.  Pp.  11,  with  plates. 

f  "The  Penokee-Gogebic  Iron-Bearing  Series  of  Michigan  and  Wisconsin," 
by  K.  D.  Irving  and  C.  E.  Van  Hise,  Mon.  U.  S.  Geol.  Surv. ,  No.  19,  1892. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       413 

Pre-Existing  Channels  and  Replacements.— When  it  is  under- 
stood that  ore-deposits  ordinarily  form  in  trunk-channels,  the 
question  as  to  whether  ores  are  deposited  in  pre-existing  open- 
ings or  are  replacements  is  easily  answered,  as  a  general  propo- 
sition. It  has  been  shown  that  solutions  cannot  be  appealed  to 
to  explain  the  original  formation  of  channels  (see  p.  295.)  The 
existence  of  channels  for  underground  circulation  must  be 
explained  by  the  original  structures  of  rocks,  or  by  the  effects 
of  deformation,  as  already  indicated.  It  therefore  follows 
that  ore-deposits  are,  to  some  extent  at  least,  deposited  in 
pre-existing  openings.  However,  the  conditions  for  vigorous 
circulation  are  also  those  for  reactions  upon  the  wall-rocks. 
It  has  been  fully  explained  that  solution  and  deposition  are 
commonly  simultaneous  processes.  Wherever  there  is  a  trunk- 
channel  it  is  certain  that  the  walls  of  the  openings  will  to  some 
extent  be  dissolved,  and  at  the  same  time  or  subsequently 
metalliferous  minerals  be  precipitated.  Indeed,  either  enlarge- 
ment by  solution  and  subsequent  precipitation  of  ore  or  syn- 
chronous solution  and  precipitation  by  which  the  wall-rocks  are 
replaced  in  various  degrees  molecule  by  molecule  by  the  ore, 
or  both  together,  are  almost  universal  phenomena. 

I  therefore  believe  that  the  large  majority  of  ore-deposits,  if  not  all, 
are  partly  deposited  in  pre-existing  openings  and  are  partly  replace- 
ments of  the  wall-rocks.  However,  in  some  cases  the  filling  of  the 
pre-existing  cavities  is  the  more  important  or  even  dominant 
process,  and  in  other  cases  substitution  for  the  wall-rocks  is  the 
more  important  or  dominant  process. 

Other  things  being  equal,  the  main  masses  of  ore-deposits 
are  more  likely  to  be  in  pre-existing  cavities  in  refractory  rocks, 
such  as  quartzite,  granite  and  porphyry ;  and  ore-deposits  which 
are  largely  replacements  are  more  likely  to  occur  in  easily  sol- 
uble rocks,  such  as  limestone.  The  gold-quartz  veins  of  Cali- 
fornia give  an  excellent  illustration  of  the  deposition  of  ores 
in  pre-existing  cavities  in  refractory  rocks,  such  as  siliceous 
argillite,  diabase,  diorite  and  granodiorite.*  This  instance  is 
all  the  more  interesting  since  the  wall-rock  itself  is  greatly 
modified,  and  has  lost  and  gained  various  elements.  Ore-de- 
posits which  are  largely  replacements  are  well  illustrated  by  the 

*  Lindgren  eft.,  pp.  172-257,  259,  261 ;  also  pp.  146-157. 


414       SOME   PRINCIPLES    CONTROLLING   DEPOSITION   OF    ORES. 

silver-lead  deposits  of  Eureka,  Nevada,  and  Leadville,  Colo- 
rado, and  by  the  gold  deposits  of  the  Judith  mountains,  Mon- 
tana.* 

Replacements  are  likely  to  be  important  also  in  proportion 
as  the  trunk-channels  are  complex  rather  than  simple.  This 
follows  from  the  law  of  mass  action.  In  proportion  as  a  trunk- 
channel  is  complex,  the  surface  of  action  upon  the  wall-rock  for 
a  given  quantity  of  solution  is  large.  As  conspicuous  examples 
where  there  are  large  surfaces  of  action  may  be  mentioned 
sandstones  and  conglomerates,  and  the  reibungs-breccias  or 
crushed  rocks  along  fault  zones.  Where  the  trunk-channels 
are  very  complex,  the  rocks  even  if  refractory  may  be  replaced 
to  a  considerable  extent  by  the  metalliferous  ores.  A  conspic- 
uous instance  of  this  in  a  sedimentary  rock  is  that  of  the  copper 
conglomerate  deposits  of  Lake  Superior,  where  many  grains, 
pebbles  and  boulders  of  porphyry  are  partly  or  wholly  replaced 
by  metallic  copper.  In  some  places  the  metallic  copper  occurs 
as  partial  or  complete  skulls  surrounding  the  boulders  of  por- 
phyry; in  other  places  these  skulls  are  thicker,  and  in  still 
other  places  the  entire  masses  of  the  boulders,  as  described  by 
Pumpelly,t  are  fully  replaced  by  the  metallic  copper.  While 
the  conglomerate  deposits  of  Lake  Superior  are  in  part  re- 
placements, they  also  are  in  large  part,  fillings  of  pre-existing 
cavities  between  the  clastic  particles.  An  excellent  example 
of  replacement  in  igneous  rocks  where  there  is  complex  dis- 
tributive faulting  and  thus  a  large  surface  of  contact  for  sub- 
stitution, is  furnished  by  the  Cripple  Creek  district,  in  which 
according  to  Penrose,J  ore  mainly  occurs  replacing  and  blend- 
ing into  various  igneous  rocks. 

In  case  of  substitution  the  entire  mass  of  the  rock  may  be 
continuously  replaced.  This  is  particularly  likely  to  occur 


*  "Silver- Lead  Deposits  of  Eureka,  Nevada,"  by  J.  S.  Curtis,  Mon.  U.  S. 
GeoL  Surv.,  No.  7,  pp.  98-99.  "Geology  and  Mining  Industry  of  Leadville," 
by  S.  F.  Emmons,  Mon.  U.  S.  GeoL  Surv.,  No.  12,  pp.  556,  569.  "  Geology  and 
Mineral  Kesources  of  the  Judith  Mountains  of  Montana,"  by  W.  H.  Weed  and 
L.  V.  Pirsson,  18th  Ann.  Rept.  U.  S.  GeoL  Surv.,  pt.  iii.,  1896-97,  pp.  594,  598. 

f  " Copper  District,"  by  E.  Pumpelly,  GeoL  of  Mich.,  vol.  i.,  for  1869-1873, 
pp.  37-38.  "Paragenesis  and  Derivation  of  Copper,"  by  E.  Pumpelly,  Am.  Jour. 
Sci.,  Third  Series,  vol.  ii.,  1871,  p.  351. 

J  "The  Mining  Geology  of  Cripple  Creek,  Colorado,"  by  E.  A.  F.  Penrose, 
Jr.,  16th  Ann.  Rept.  U.  S.  GeoL  Surv.,  pt.  ii.,  pp.  140-141,  144-146,  161-162. 


SOME   PRINCIPLES   CONTROLLING  DEPOSITION   OF    ORES.      415 

where  the  rock  is  uniform  in  structure  and  composition,  as 
limestone  or  dolomite.  Where,  however,  the  rock  is  of  com- 
plex composition  such  as  granite  or  porphyry ;  or  where  there 
are  different  kinds  of  rock  present,  as,  for  instance,  diorite  and 
granite,  the  replacement  will  usually  be  largely  selective.  This 
selective  replacement  may  apply  to  the  mass  of  the  wall-rock, 
to  the  individual  fragments  of  it,  to  clastic  fragments  of  sand- 
stones or  conglomerate,  to  the  different  constituent  minerals  in 
a  single  fragment.  The  particular  minerals  or  masses  which 
are  most  soluble  in  the  solutions  present  will  be  most  rapidly 
dissolved. 

Where  the  wall-rock  varies  greatly  in  the  solubility  of  its 
minerals,  the  selective  replacement  of  the  country-rock  may  ex- 
tend for  some  distance  from  the  central  deposits.  The  readily- 
soluble  minerals  are  dissolved,  and  in  place  of  them  there  are 
precipitated  the  metalliferous  minerals.  This  process  is  ordi- 
narily called  impregnation.  Selective  replacement  of  this  kind 
is  well  illustrated  by  the  Butte,  Montana,  granite,  in  which 
"  the  basic  constituents  of  the  granite  are  naturally  attacked 
first,  then  the  feldspars,  and  finally  the  quartz  itself  may  be 
removed,  so  that  in  some  parts  there  are  found  large  masses, 
composed  entirely  of  metallic  minerals."* 

In  the  variable  solubility  of  the  country-rock  lies  the  partial 
explanation  in  regions  of  heterogeneous  rocks  of  the  frequent 
occurrence  of  the  main  masses  of  the  ore-deposit  in  the  more 
soluble  rock.  For  instance,  where  limestone  and  sandstone, 
limestone  and  quartzite,  limestone  and  diorite,  limestone  and 
trachyte,  limestone  and  porphyry,  limestone  and  granite,  or 
limestone  with  almost  any  other  rock  occur  in  intimate  asso- 
ciation and  ore-deposits  are  found,  the  ore  is  likely  to  be  largely 
in  the  limestone. f  The  partial  explanation  of  this  relation  is 
undoubtedly  the  more  ready  solubility  of  the  limestones.  How- 
ever, other  factors  enter  into  the  matter.  It  has  already  been 
explained  that  the  country-rock  may  furnish  solutions  which 


*  "Notes  on  the  Geology  of  Butte,  Montana,"  by  S.  F.  Emmons,  Trans.j  xvi., 
1888,  57. 

f  "The  Copper  Ores  of  the  Southwest,"  by  Arthur  F.  Wendt,  Trans.,  xv.,  25- 
77.  "  Silver- Lead  Deposits  of  Eureka,  Nevada,"  by  Jos.  Story  Curtis,  Mon. 
U.  S.  Geol.  Surv.,  No.  7.  "Geology  and  Mining  Industry  of  Leadville,"  by  S. 
F.  Emmons,  Mon.  U.  S.  Geol.  Surv.,  No.  12,  p.  540. 


416       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF     ORES. 

react  upon  the  mineral-bearing  solutions,  and  thus  cause  pre- 
cipitation (see  pp.  317—319).  Furthermore,  where  limestone  and 
stronger  rocks  are  deformed  together,  the  limestone,  having 
less  strength,  is  more  likely  to  be  crushed  and  broken  in  a  com- 
plex manner  and  thus  furnish  trunk-channels  for  circulation. 

In  conclusion,  I  insist  that  ore-deposits  form  where  there 
existed  original  trunk-channels  of  circulation.  These  trunk- 
channels  may  have  been  greatly  enlarged  by  solution.  This, 
indeed,  is  the  general  tendency  above  the  level  of  groundwater, 
but  the  general  tendency  below  the  level  of  groundwater  is 
to  cement  rather  than  to  enlarge  the  openings  (see  p.  329). 
Ore-deposits  formed  along  trunk-channels  will  commonly,  if 
not  universally,  be  to  some  extent  in  pre-existing  openings  and 
to  some  extent  as  a  substitution  for  the  wall-rock.  Where  the 
trunk-channels  are  simple  and  the  rocks  are  refractory  the  ore- 
deposits  to  a  large  extent  are  likely  to  be  in  pre-existing  open- 
ings. Where  the  trunk-channels  are  complex  and  the  rocks 
soluble  the  ore-deposits  to  a  large  extent  are  likely  to  be  re- 
placements. 

Character  of  the  Topography. 

Effect  of  the  Vertical  Element. — Where  the  topography  is 
marked  the  underground  circulation  is  likely  to  penetrate 
much  deeper  than  in  regions  where  the  variations  in  topog- 
raphy are  slight. 

In  mountainous  and  elevated  plateau  regions  the  lithosphere 
is  likely  to  have  more  numerous,  larger,  and  deeper  openings 
than  in  low-lying  areas.  Elevated  areas  are  those  of  compara- 
tively recent  orogenic  or  epeirogenic  movement.  Therefore 
they  are  regions  in  which  the  rocks  have  recently  been  de- 
formed and  fractured,  and  hence  the  processes  of  cementation 
would  have  been  less  likely  to  have  closed  the  openings.  In 
regions  of  very  steep  topography  the  tendency  for  the  material 
to  glide  down  the  slope  under  the  stress  of  gravity  also  tends 
to  widen  openings  which  have  been  once  formed.  Such  move- 
ments are  known  to  be  effective  to  the  depth  of  hundreds  of 
meters.  It  is  hence  clear  that  elevated  and  rough  regions  are 
those  in  which  the  underground  circulation  is  likely  to  find 
large,  numerous,  and  deep  openings. 

Furthermore,  elevated  and  mountainous  re'gions  are  those  in 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       417 

which  the  underground  water  has  the  greatest  difference  in 
head,  and  this  is  favorable  to  deep  circulation. 

Thus,  in  mountainous  regions,  like  the  Cordilleras,  it  would 
be  expected  that  the  underground  circulation  both  ascending 
and  descending  would  be  effective  to  greater  depths  upon  the 
average,  than  in  regions  of  gentle  topography  like  that  of  the 
lead  and  zinc  district  of  southwestern  Wisconsin  (see  Fig.  7,  p. 
401),  where  it  is  perhaps  probable  that  the  scope  of  the  effective 
circulation,  ascending  and  descending,  is  confined  to  a  vertical 
distance  of  500  meters  or  less. 

Unfortunately,  the  majority  of  descriptions  of  mines  do  not 
say  anything  as  to  the  level  of  groundwater.  In  the  San  Juan 
district  of  Colorado,  which  is  a  region  of  very  rugged  topog- 
raphy, Purington  states*  that  the  level  of  groundwater  is  far 
below  the  surface,  and  that  oxidizing  effects  are  produced  at 
a  depth  of  300  meters  or  more,  thus  confirming  the  conclu- 
sion that  the  zone  of  descending  water  is  increased  by  rugged 
topography,  and  it  can  hardly  be  doubted  that  the  zone  of 
effective  ascending  circulation  is  equally  increased. 

Effect  of  the  Horizontal  Element. — The  horizontal  position  of 
an  ore-deposit  with  reference  to  topography  often  has  an  im- 
portant influence  upon  its  richness  and  magnitude.  If  the 
correct  theory  of  circulation  of  underground  waters  and  the 
deposition  of  ores  has  been  given,  certain  corollaries  follow  from 
this  theory  with  reference  to  this  point. 

(1)  Commonly  ores  deposited  by  ascending  waters  would  be 
formed  below  the  valleys,  or  at  least  below  the  lower  parts  of 
the  slopes ;  for  these  are  the  places  where  waters  are  ascending 
in  the  trunk-channels.  (2)  Commonly  ores  deposited  by  de- 
scending waters  would  be  formed  below  the  crests  or  below  the 
upper  slopes  of  elevations ;  for  these  are  the  places  where  water 
would  be  descending.  Probably  the  upper  slopes  would  be  more 
favorable  places  than  the  crests ;  for  at  an  annular  belt  upon  the 
upper  slope  of  an  elevation  the  quantity  of  descending  waters 
would  be  greater  than  at  the  crests.  (3)  Commonly  ores  which 
receive  a  first  concentration  by  ascending  waters  and  a  second 
concentration  by  descending  waters  would  be  on  the  slopes, 

*  "  Preliminary  Keport  on  the  Mining  Industries  of  the  Telluride  Quadrangle, 
Colorado,"  by  C.  W.  Purington,  18^  Ann.  Eept.  U.  S.  Geol  Surv.,  pt.  iii.,  1896- 
97,  pp.  825-827. 


418      SOME    PRINCIPLES    CONTROLLING   DEPOSITION   OP    ORES. 

probably  in  many  instances  nearer  the  valleys  than  the  crests. 
At  such  places  the  meteoric  waters  falling  at  the  higher  eleva- 
tions would  have  sufficient  head  to  deeply  search  the  zone  of 
fracture  for  ores.  Therefore,  the  ascending  circulation  in  trunk- 
channels  would  be  strong.  Furthermore,  at  such  places  the  level 
of  groundwater  would  be  a  considerable  distance  below  the  sur- 
face, and  abundant  descending  waters  would  be  concentrated 
in  the  upper  parts  of  the  openings.  (See  Fig.  6,  p.  336.)  The 
downward  migration  of  the  belt  of  weathering  would  furnish 
the  final  favorable  condition  for  the  accumulation  of  a  large 
amount  of  second  concentrates  by  descending  waters. 

Admirable  illustrations  of  ore-deposits  corresponding  to  the 
second  of  the  corrollaries  are  furnished  by  the  iron-ore-deposits 
of  the  Lake  Superior  region.  These  are  the  products  of  de- 
scending waters,  and  the  great  majority  of  the  ore-deposits  are 
found  near  the  tops  of  hills  or  upon  the  upper  slopes. 

An  excellent  illustration  of  the  third  corrollary  is  furnished 
by  the  lead  and  zinc  district  of  the  upper  Mississippi  valley. 
Chamberlin*  notes  that  in  the  valleys  of  the  "Wisconsin  part  of 
the  district  the  waters  generally  ascend  to  the  surface ;  therefore, 
at  such  places  only  a  first  concentration  would  be  expected,  and 
it  is  the  general  impression  among  miners  that  a  lode  makes 
better  on  the  slope  of  a  hill  "  than  at  the  summit  or  at  the  foot 
of  a  hill."t  Furthermore,  it  is  held  by  the  miners  that  the 
lodes  which  run  parallel  to  a  contour  of  a  hill  "  like  an  eave- 
trough,"  are  more  likely  to  be  rich  than  those  which  run  toward 
the  summit  of  the  hill.J  Both  of  these  practical  conclusions 
of  the  miners  are  fully  explained  by  the  theory  of  a  first 
concentration  by  ascending  waters,  and  a  second  concentration 
by  descending  waters  when  considered  in  connection  with  the 
topography. 

The  above  conclusions  concerning  the  relations  of  ore-de- 
posits and  topography  are  only  perfectly  applicable  in  regions 
in  which  the  drainage  lines  have  been  reasonably  stable.  The 
Lake  Superior  region  and  the  lead  and  zinc  district  of  the 
upper  Mississippi  valley  are  regions  of  stable  topography.  The 
main  drainage  lines  have  probably  not  been  greatly  modified 

*  Chamberlin,  cit.t  p.  565. 
I  Chamberlin,  cit.,  p.  563. 
£  Chamberlin,  cit.,  p.  563. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.      419 

since  they  were  established  at  the  close  of  the  Cretaceous  period 
of  base  levelling.  This  is  certainly  true  of  the  lead  and  zinc 
district ;  but  in  the  Lake  Superior  region  the  drainage  lines 
have  been  to  some  extent  modified  by  the  glacial  invasions. 

In  regions  in  which  there  have  been  recent  important  changes 
in  the  positions  of  the  drainage  lines  and  elevations,  the  gen- 
eralizations are  only  partly  applicable.  It  is  well  known,  in 
consequence  of  the  varying  hardness  of  rocks,  in  consequence 
of  their  structure,  in  consequence  of  the  unequal  strength  of 
streams  and  unequal  declivity,  that  drainage  lines  are  almost 
constantly  shifting,  and  in  many  regions  somewhat  rapidly. 
Consequent  on  this  shifting,  many  ore-deposits  which,  when 
below  valleys,  received  a  first  concentration  by  ascending 
waters,  are  now  well  up  on  slopes  or  even  at  crests.  A  change 
of  this  kind  would  be  especially  favorable  to  the  development 
of  ore-deposits  which  are  due  to  two  concentrations,  the  first 
by  ascending  and  the  second  by  descending  waters.  In  an 
early  stage  of  the  history  of  a  deposit  it  would  be  in  the  most 
favorable  place  to  receive  a  first  contribution  of  ore.  Later, 
when,  as  a  consequence  of  a  topographic  change,  it  was  on 
higher  ground,  it  would  then  be  in  a  favorable  place  for  the 
work  of  descending  waters.  Although  it  is  difficult  to  prove, 
I  have  little  doubt  that  many  ore-deposits  have  had  this  very 
favorable  history. 

Many  other  ways  could  be  suggested  in  which  changing 
topography  would  be  favorable  or  unfavorable  to  further  con- 
centration of  ores.  However,  I  shall  not  attempt  this,  but 
suggest  that  geologists  in  various  regions  study  the  ores  in 
connection  with  the  topographic  development  of  the  region. 
Such  studies  will  furnish  facts  upon  which  safe  generalizations 
may  be  made. 

Physical  Revolutions. 

The  genesis  of  many  ore-deposits  is  undoubtedly  further 
complicated  by  physical  revolutions  of  various  kinds.  After 
an  ore-deposit  has  partly  formed,  either  by  ascending  or  de- 
scending waters  or  both,  the  region  may  go  through  a  physical 
revolution,  and  after  the  revolution  the  concentration  of  the 
ores  may  again  be  taken  up  by  Nature's  processes. 

After  an  ore-deposit  has  been  formed  the  country  may  be 
reduced  to  the  level  of  the  sea  either  by  denudation  or  sub- 

27 


420      SOME    PRINCIPLES    CONTROLLING   DEPOSITION   OF    ORES. 

sidence;  there  be  deeply  buried  under  sedimentary  rocks; 
may  be  again  uplifted,  and  undergo  a  second  cycle  of  reactions 
which  affect  the  nature  of  the  ore-deposits.  An  ore-deposit 
partly  formed  may  be  buried  deep  under  volcanic  rocks.  This 
undoubtedly  has  occurred  on  a  great  scale  through  the  great 
period  of  Tertiary  vulcanism  in  the  Cordilleras  of  the  West. 
The  ore-deposits  there  buried  are  placed  in  a  new  environment, 
and  are  undergoing  a  second  cycle  of  concentration  or  deple- 
tion. When  in  the  future  denudation  shall  have  stripped  off 
these  volcanics,  these  ore-deposits  will  be  at  the  surface.  This 
may  not  occur  while  man  occupies  the  earth,  but  doubtless 
similar  things  have  occurred  with  reference  to  extensive  areas 
where  mines  are  now  being  worked.  It  is  well  known  that 
when  fissures  once  form,  these  are  places  of  weakness,  and  that 
movement  has  again  and  again  recurred  along  the  old  planes. 
Thus,  where  the  conditions  once  become  favorable  for  ore-con- 
centration they  may  recur  in  the  same  places  through  various 
revolutions.*  Physical  changes  of  various  other  kinds  may  take 
place.  Each  of  the  complex  changes  in  physical  history  will 
produce  its  effect  upon  an  ore-deposit. 

General. 

It  is  clear  from  the  foregoing  that  an  ore-deposit  may  not 
represent  the  work  of  a  single  period  of  ascending  waters,  but 
may  include  several  alternating  periods  of  ascension  and  descen- 
sion,  and  in  this  way  irregularities  in  certain  of  the  ore-deposits 
in  very  ancient  rocks  may  be  explained.  However,  it  appears 
probable  in  many  cases  that  the  main  work  of  ore  deposition 
has  been  the  result  of  a  single  concentration  by  ascending 
waters  and  a  single  concentration  by  descending  waters. 

Any  of  the  special  and  local  factors  above  discussed  and 
others  may  in  an  individual  case  be  so  conspicuous  as  to  ap- 
pear to  be  a  controlling  factor  in  the  formation  of  an  ore-deposit. 
One  might  say  that  the  existence  of  a  given  trough  was  the 
cause  of  the  production  of  an  ore-deposit.  The  truer  state- 
ment would  be  that  the  factor  under  consideration  is  one 
essential  factor  among  many.  The  porosity  of  a  formation, 
the  existence  of  a  pitching  trough,  favorable  topography,  the 
presence  of  igneous  rocks  furnishing  heat  to  make  the  waters 
active,  and  many  other  special  factors,  may,  in  a  given  case,  all 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION   OF    ORES.       421 

be  essential  factors,  without  the  help  of  any  one  of  which  an 
ore-deposit  would  not  have  been  produced.  But  no  combina- 
tion of  these  special  factors  will  form  an  ore-body,  if  a  source 
of  the  metal  is  not  available  upon  which  the  underground 
waters  may  act.  In  short,  each  case  of  the  formation  of  an 
ore-deposit  requires  the  fortunate  combination  of  many  favor- 
able factors,  working  harmoniously  together,  the  absence  of 
any  one  of  which  may  prevent  the  concentration  of  the  ore- 
deposit. 

ORE-CHUTES.* 

No  fact  is  better  known  concerning  ore-deposits  than  that 
they  vary  in  the  most  remarkable  fashion,  both  in  size  and 
richness.  Moreover,  these  variations  are  both  vertical  and 
horizontal.  Frequently  rich  deposits  decrease  in  size  or  are 
wholly  cut  off  with  extraordinary  abruptness.  Other  equally 
rich  deposits  may  appear  somewhere  else  on  the  same  level  or 
on  another  level  in  an  equally  strange  and  apparently  inex- 
plicable manner.  The  ore-masses  of  exceptional  richness  are 
generally  called  ore-chutes.  Sometimes  they  are  spoken  of  as 
pay-streaks,  at  other  times  as  bonanzas,  at  other  times  as  chim- 
neys. In  this  paper  ore-chute  is  used  as  a  general  term  to 
include  all  deposits  of  exceptional  richness  or  size,  of  whatever 
origin.  At  various  places  in  this  paper  factors  have  been  men- 
tioned which  produce  ore-chutes.  However,  because  of  the 
very  great  economic  importance  of  ore-chutes,  it  seems  to  me 
advisable  to  consider  under  one  heading  some  of  the  more 
prominent  of  these  factors,  even  at  the  risk  of  repetition. 

Ore-chutes  may  be  grouped  into  those  which  are  largely  ex- 
plained (A)  by  structural  features,  (B)  by  the  influence  of  the 
wall-rocks,  and  (C)  by  a  secondary  concentration  by  descending 
waters. 

(A)  One  large  class  of  ore-chutes  may  be  explained  princi- 
pally by  structural  features.  These  structural  features  may  be 
(1)  the  varying  size,  (2)  varying  complexity,  (3)  flexures,  (4)  in- 
tersections of  fractures,  and  (5)  later  orogenic  movements. 

(1)  A  fracture  through  a  mass  of  rocks  is  necessarily  uneven. 
Where  there  are  movements,  it  follows  that  the  walls  will  not 

*  For  a  general  discussion  of  ore-chutes  in  fissures,  see  "The  Mining  Geology 
of  the  Cripple  Creek  District,"  by  K.  A.  F.  Penrose,  Jr.,  16^  Ann.  Eept.  U.  S. 
Geol.  Survey,  partii,,  1894-1895,  pp.  162-166. 


422       SOME   PRINCIPLES    CONTROLLING   DEPOSITION   OF    ORES. 

be  adjusted  to  each  other.  Where  projections  or  complex  sur- 
faces are  opposite  each  other,  the  fissure  may  be  represented 
by  a  mere  seam.  Where,  on  the  other  hand,  depressions  or 
two  concave  surfaces  are  opposite  each  other,  a  widening  may 
occur  which  in  some  cases  is  sufficient  to  produce  a  great  room. 
Rooms  may  be  partly  or  largely  produced  by  solution.  Eooms 
may  be  connected  by  comparatively  large  channels.  Thus 
there  may  be  in  a  single  mine  a  succession  of  rooms  filled  with 
rich  deposits  connected  with  rich  chimneys.  It  is  evident  from 
the  above  that  there  may  be  every  variation  in  the  width  of  an 
ore-deposit  due  to  this  factor,  from  zero  to  many  feet. 

It  has  been  shown,  other  things  being  equal,  that  the  under- 
ground circulation  will  follow  the  largest  openings.  Thus, 
wherever  there  are  rooms,  and  especially  where  there  are 
rooms  with  connecting  passages  of  considerable  width,  there 
the  most  abundant  circulation  will  be  converged.  Moreover, 
the  solutions  of  this  circulation  will  be  derived  from  various 
sources.  Hence,  in  the  large  openings  more  ore  and  very  fre- 
quently richer  ore  will  be  deposited  than  in  the  narrower  open- 
ings, where  the  solutions  are  both  less  abundant  and  less  com- 
plex. 

(2)  Ore-chutes  are  frequent  where  the  fractures,  instead  of 
being  simple,  are  complex;  that  is,  where  there  is  a  crushed 
zone,  or  zone  of  brecciation  and  mashing.     It  has  been  pointed 
out  pp.  343-345)  that   some   ore-deposits   are   largely  due   to 
reactions  between  the  solutions  and  the  rocks  through  which 
they  pass.     Such  an  ore-deposit  is  most  likely  to  be  rich  at  a 
crushed  zone,  where    there   is    every  opportunity   for    much 
greater  interaction  between  the  solutions  of  the  trunk-channels 
and  the  rocks  through  which  it  circulates  than  where  there  is 
a  single  fracture,  even  if  the  space  furnished  by  the  latter  is 
greater  than  that  furnished  by  the  multitude  of  smaller  open- 
ings.    (See  p.  414.) 

(3)  Very  frequently  the  rich  chutes  of  ore   are  located  by 
flexures,  the  ore  being  either  at  the  crests  of  anticlines  or  at 
the  bottoms  of  synclines.     As  pointed  out  (pp.  405-412),  this 
is  especially  likely  to  be  the  case  where,  in  connection  with  the 
folds,  there  are  impervious  strata.     Under  such  circumstances, 
as  has  already  been  fully  explained,  ore  is  likely  to  be  con- 
verged from  ascending  solutions  in   the   arches  of  pervious 


SOME   PRINCIPLES   CONTROLLING  DEPOSITION   OF    ORES.      423 

strata  below  impervious  strata,  and  by  descending  waters  in 
troughs  of  pervious  strata  above  impervious  strata.  In  the 
cases  cited,  such  as  those  of  Australasian  and  Nova  Scotian 
gold-ores  and  the  Lake  Superior  iron-ores,  these  relations  are 
perfectly  clear ;  but  doubtless  in  many  mines  there  are  minor 
flexures  which  have  been  overlooked,  but  which  may  be  suffi- 
cient to  control  the  movement  of  the  circulation,  and  thus  pro- 
duce the  chimneys  of  ore.  These  minor  flexures  may  be  par- 
allel with  the  dip  of  a  deposit,  or  they  may  pitch  to  the  right 
or  to  the  left  of  a  deposit  as  one  looks  down  the  dip. 

(4)  The  intersections  of  fractures  furnish  one  of  the  most 
frequent  explanations  of  ore-chutes.  The  intersections  may  be 
those  of  faulted  fissures;  those  of  fissures  and  joints,  or  the 
intersections  of  joints.  In  many  instances  one  set  of  fractures 
carries  the  larger  ore-deposits,  and  the  intersecting  set  or  sets 
of  fractures  are  known  as  side  fractures.  In  other  instances 
the  main  deposits  may  occur  in  more  than  one  set  of  fractures, 
and  still  other  sets  of  less  importance  constitute  the  side  frac- 
tures. 

In  all  cases  where  intersecting  fractures  occur,  there  solu- 
tions will  be  contributed  from  two  or  more  sources.  The  solu- 
tions will  invariably  have  different  compositions,  and,  therefore, 
precipitation  will  be  likely  to  occur  at  the  junctions.  In  some 
cases  more  than  one  set  of  fractures  may  furnish  metalliferous 
material,  while  in  other  cases  the  metalliferous  material  may 
be  contributed  by  one  set  of  fractures  and  the  precipitating 
agents  by  the  others.  In  these  instances  where  the  intersecting 
veins  all  carry  ore,  it  is  easy  to  see  why  the  deposits  at  the  inter- 
sections should  be  unusually  large  and  rich.  However,  where 
the  side  veins  are  small  or  are  wholly  filled  with  gangue  ma- 
terial, their  importance  in  the  genesis  of  ore-deposits  has  been 
very  generally  overlooked.  In  many  instances  there  is  little 
doubt  that  the  metallic  material  has  been  precipitated  in  a  main 
fissure  at  or  near  where  the  side  veins  join  through  the  influ- 
ence of  the  solutions  contributed  by  the  latter  veins.  A  very 
clear  case  of  the  influence  of  side  veins  is  that  already  cited  of 
the  Enterprise  mine,  of  Rico,  Colorado,  where  the  pay-chutes 
are  especially  rich  in  the  main  fissures  at  the  places  where  bar- 
ren side  veins  intersect  them.  Where  ore-chutes  are  found  to 
be  connected  structurally  with  barren  side  veins,  a  considera- 


424      SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

tion  of  the  minerals  themselves  and  the  minerals  in  the  side 
veins  ought  to  lead  to  more  exact  knowledge  concerning  the 
manner  of  the  precipitation  of  the  metal ;  for  presumably  the 
precipitation  of  the  metals  was  connected  with  some  of  the 
compounds  which  occur  as  gangue  in  the  side  veins. 

Side  fractures  may  be  at  right  angles  to  the  main  set  of 
fractures  or  incline  to  them.  They  may  extend  directly  down 
the  dip  or  pitch  to  the  right  or  left  along  the  dip.  Therefore, 
almost  any  curious  distribution  of  the  rich  chutes  may  occur. 
In  some  cases  a  side  stream  either  bearing  metals  or  precipitat- 
ing agents,  or  both,  may  not  issue  equally  all  along  a  fault  or 
a  joint,  but  may  be  largely  converged  into  a  single  channel  or 
strong  spring  which  enters  a  fissure.  In  such  cases,  especially 
if  the  spring  empties  where  there  is  a  room  produced  by  the 
structural  features  discussed  under  (1),  bonanzas  may  be  formed, 
such  as  those  of  the  Comstock  lode. 

"While  the  relative  influence  of  the  different  sets  of  intersect- 
ing fractures  is  very  complex,  in  an  individual  mine  a  close 
study  of  the  number,  order  and  relations  of  the  fractures  and 
joints,  many  of  which  are,  perhaps,  almost  imperceptible,  may 
furnish  rules  which  will  enable  one  to  more  intelligently  search 
for  ore. 

Between  the  two  cases  of  a  trunk-channel  produced  by  flex- 
ure, described  under  (3),  and  by  cross  fracture  described  under 
(4),  there  is  complete  gradation. 

(5)  Late  orogenic  movements  explain  certain  ore-chutes. 
After  openings  have  received  a  first  contribution  of  ore,  and 
are,  perhaps,  fully  cemented  by  ore  and  gangue  materials,  oro- 
genic movements  frequently  recur,  which  again  fracture  the 
ground  and  produce  openings.  Some  parts  of  a  deposit  may 
escape  fracture,  while  other  parts  may  be  broken.  The  fractur- 
ing of  the  broken  parts  may  be  simple  or  complex.  The  com- 
plex fracturing  may  produce  zones  of  parallel  fractures,  zones 
of  intersecting  fractures,  brecciated  zones,  or  even  zones  in 
which  the  material  is  finely  mashed.  Between  the  parts  of  the 
deposit  which  have  no  fracturing  and  those  in  which  the  frac- 
turing is  of  the  most  complex  sort,  there  may  be  all  gradations. 
The  fractures  may  be  confined  to  a  narrow  belt  of  a  deposit  or 
to  one  side  of  it.  It  may  be  confined  within  varying  limits 
laterally  or  vertically.  All  of  the  above  statements  in  refer- 


SOME   PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.      425 

ence  to  the  main  deposits  apply  equally  well  to  intersecting 
sets  of  deposits ;  also,  entirely  new  sets  of  openings  may  be  pro- 
duced. Therefore,  an  ore-deposit  which  has  received  a  first 
contribution,  and  again  is  subjected  to  orogenic  movements,  is 
in  such  a  condition  that  it  may  again  receive  a  contribution  of 
ore  material  under  the  same  complex  laws  as  at  first.  This 
ore  material  will  be  distributed  in  the  same  irregular  manner 
as  that  of  the  first  contribution.  Therefore,  the  new  material 
will  not  only  be  distributed  irregularly,  but  will  be  superim- 
posed upon  the  old  material,  which  also  had  an  irregular  dis- 
tribution, and  thus  there  will  be  extraordinary  variations  in 
richness. 

(B)  Ore-chutes  in  many  cases  are  explained  by  the  influence 
of  the  wall  rocks.     It  is  well  known  that  where  ore-deposits 
intersect  a  complex  set  of  rocks,  that  the  pay-chutes  are  likely 
to  have  a  decided  preference  for  one  rock  rather  than  the  others. 
For  instance,  if  a  fissure  passes  from  granite  to  diorite,  or  from 
either  of  these  to  limestone,  or  from  any  of  these  to  sandstone, 
the  character  and  richness  of  the  deposit  may  vary  greatly  as 
the  rock  changes.     For  this  variability,  due  to  the  character  of 
the  wall  rocks,  different  explanations  apply  in  different  cases. 
(1)  In  some  instances  the  restriction  of  the  ore-chutes  to  one 
rock  is  largely  explained  by  the  more  ready  solubility  of  that 
rock.    This  is  particularly  applicable  to  the  substitution  deposits, 
the  wall  rock  being  dissolved  pari-passu  with  the  deposition  of 
the  ore.    By  the  solution  of  the  soluble  rock  sufficient  room  is 
furnished  for  a  large  ore-deposit.     The  above  is  undoubtedly 
the  partial  explanation  in  many  cases  of  the  preference   of 
the  ores  for  limestone  rather  than  to  the  adjacent  more  insolu- 
ble rocks.    (2)  In  other  instances  the  preference  of  the  rich  and 
large  bodies  to  one  wall-rock  rather  than  another  is  due  to  the 
fact  that  the  wall  rock  itself,  by  reaction  upon  the  solutions, 
precipitates  the  ore  material.     This  may  also  partly  explain  the 
preference  of  certain  ore-deposits  for  limestone.     (3)  In  still 
other  instances  the  wall  rock  itself  furnishes  solutions  contain- 
ing metalliferous  material  which  is  precipitated  in  the  trunk- 
channels,  or  furnishes  solutions  capable  of  precipitating  metal- 
liferous material  in  the  trunk-channel. 

(C)  A  third  class  of  ore-chutes  are  those  produced  by  the 
processes  which  have  been  so  fully  explained  in  this  paper,  viz. : 


426       SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 

the  secondary  enrichment  of  a  deposit  by  descending  waters,  the 
first  enrichment  of  which  was  produced  by  ascending  waters. 
By  this  process  rich  ore-bodies,  either  oxidized  or  sulphuretted, 
or  partly  each,  which  are  limited  in  depth  by  the  distance  to 
which  the  descending  waters  are  effective,  are  formed. 

General. — Of  necessity,  in  this  analysis,  the  various  factors 
which  may  produce  ore-chutes  have  been  separately  treated. 
However,  in  a  given  case  it  is  rare,  indeed,  to  find  that  the  en- 
tire explanation  lies  in  the  application  of  a  single  one  of  them. 
To  explain  an  ore-chute  of  an  individual  mine,  ordinarily  a 
number  of  the  above  causes  need  to  be  combined,  and  in  some 
cases,  doubtless,  other  causes  which  have  not  been  treated.  No 
study  is  more  important  economically,  more  fascinating,  or  more 
difficult  in  a  given  district  or  mine  than  to  ascertain  the  par- 
ticular combination  of  factors  which  produce  the  ore-chutes. 

From  the  foregoing  it  is  plain  that  no  general  statement  can 
be  made  in  explanation  of  ore-chutes.  In  each  individual  dis- 
trict, more,  in  each  individual  mine,  still  further,  in  each  indi- 
vidual part  of  a  mine,  all  the  phenomena  there  occurring  must 
be  closely  studied  in  the  light  of  a  correct  theory  of  ore-deposi- 
tion in  order  to  reach  an  explanation  applicable  to  the  particu- 
lar case. 

It  is  well  known  in  the  districts  which  are  mineralized  that 
the  workable  ore-deposits  are  ordinarily  confined  to  relatively 
small  areas,  although,  so  far  as  one  can  see,  the  amount  of 
metalliferous  material  to  furnish  ore-deposits  may  have  been 
the  same  throughout  the  districts.  The  explanation  of  the  lack 
of  workable  ore-deposits  for  larger  parts  of  the  districts  ordi- 
narily lies  in  the  lack  of  the  favorable  combination  of  the  vari- 
ous special  factors  mentioned,  and  doubtless  many  others  which 
have  not  been  considered.  As  better  illustrating  my  meaning, 
I  may  again  mention  the  iron-ores  and  copper-ores  of  the  Lake 
Superior  region.  The  iron-bearing  formation  has  an  extensive 
occurrence  throughout  the  Lake  Superior  region.  The  work- 
able iron-ores  are,  however,  confined  to  small  areas,  in  which 
there  have  been  happy  combinations  of  ancient  and  recent 
metamorphism  combined  with  favorable  structural  features. 
The  Lake  Superior  copper-deposits  equally  well  illustrate  the 
principle.  All  of  the  mines  now  being  exploited  are  confined 
to  an  exceedingly  narrow  area  on  Keweenaw  Point.  But  the 


SOME   PRINCIPLES   CONTROLLING   DEPOSITION    OF    ORES.       427 

copper-bearing  rocks  occupy  an  extensive  area  about  the  entire 
Lake  Superior  basin.  Moreover,  these  copper-bearing  rocks 
are  mineralized  in  many  places,  as  is  shown  by  the  widely 
disseminated  copper.  But,  unfortunately,  in  many  areas  a  little 
copper  is  concentrated  in  many  amygdaloid  or  sandstone  belts 
rather  than  in  a  single  amygdaloid  or  sandstone.  For  instance, 
in  certain  districts  scores  of  amygdaloid  beds  lie  upon  one  an- 
other. The  scoriaceous  upper  surface  of  each  of  these  beds 
bears  metallic  copper,  but  none  of  them  in  sufficient  amount  .so 
that  the  copper  is  a  workable  deposit.  Had  the  copper  de- 
posited in  a  number  of  these  amygdaloid  formations  been  con- 
centrated in  one  of  them,  a  workable  ore-deposit  would  have 
been  produced. 

From  the  foregoing  it  is  clear  that  an  investigation  of  the 
local  factors  in  a  district  should  include  both  those  which  are 
favorable  to  concentration  of  ores  and  those  which  prevent  the 
concentration  of  ores,  for  a  study  of  the  latter  in  many  districts 
may  prevent  the  expenditure  of  large  sums  in  exploration  where 
the  mineralization  is  general  but  the  conditions  are  not  such  as 
to  have  concentrated  the  valuable  material  in  sufficient  quantity 
at  any  one  position  to  warrant  exploitation. 

A  treatise  on  ore-deposits,  including  descriptions  of  indi- 
vidual districts,  necessarily  deals  in  each  area  with  the  special 
factors  which  are  important  in  that  district.  These  special  fac- 
tors may  be  considered  so  conspicuous  that  the  entire  attention 
is  given  to  them.  However,  it  is  to  be  remembered  that  each 
of  these  is  subordinate  to  the  general  principles  controlling  the 
deposition  of  ore-deposits  in  all  districts. 

THE  CLASSIFICATION  OF  ORE-DEPOSITS. 

Before  giving  the  classification  of  ore-deposits  which  follows 
from  the  foregoing  treatment,  it  may  be  well  to  briefly  recall 
the  most  fundamental  features  of  the  water  circulation  which 
produces  the  ore-deposits.  First  comes  the  action  of  the  down- 
ward-moving, lateral-moving  waters  of  meteoric  origin  which 
take  into  solution  metalliferous  material.  These  waters  are 
converged  in  trunk-channels,  and  there  while  ascending  the 
first  concentration  of  ore-deposits  may  result.  After  this  first 
concentration,  many  of  the  ore-deposits  which  are  worked  by 
man  have  undergone  a  second  concentration  not  less  important 


428       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

than  the  first,  as  result  of  descending,  lateral-moving  waters.  In 
other  cases  a  concentration  by  descending,  lateral-moving  waters 
alone  is  sufficient  to  explain  some  ore-deposits.  It,  therefore, 
appears  more  clearly  than  heretofore  that  an  adequate  view  of 
ore-deposits  must  not  be  a  descending  water  theory,  a  lateral- 
secreting  water  theory,  or  an  ascending  water  theory  alone. 
While  an  individual  ore-deposit  may  be  produced  by  one  of 
these  processes,  for  many  ore-deposits  a  complete  theory  must  be  a 
descending,  lateral-secreting,  ascending,  descending,  lateral-secreting 
theory.  The  descending,  lateral-moving,  and  ascending  waters 
are  alike  driven  by  gravity.  Each  performs  its  own  work. 

We  have  now  only  to  bring  together  in  summary  the  different 
groups  and  classes  of  ore-deposits  which  have  been  considered 
to  have  a  satisfactory  genetic  classification  of  ores  deposited 
by  underground  waters.  As  already  noted,  ore-deposits  may 
be  divided  into  three  groups  :  (A)  ores  of  igneous  origin,  (B) 
ores  which  are  the  direct  result  of  the  processes  of  sedimen- 
tation, and  (C)  ores  which  are  deposited  by  underground 
water. 

Since  the  ores  produced  by  igneous  agencies  and  those  pro- 
duced by  processes  of  sedimentation  have  not  been  considered 
in  this  paper,  a  subdivision  of  these  groups  will  not  be 
attempted. 

Ores  resulting  from  the  work  of  groundwater,  group  (C) 
above,  may  be  divided  into  three  main  classes  : 

(a)  Ores  which  at  the  point  of  precipitation  are  deposited  by 
ascending  waters  alone.     These  ores  are  usually  metallic,  or 
some  form  of  sulphuret ;  but  they  may  be  tellurides,  silicates 
or  carbonates. 

(b)  Ores  which  at  the  place  of  precipitation  are  deposited  by 
descending  waters  alone.     These   ores   are   ordinarily  oxides, 
carbonates,  chlorides,  etc. 

(c)  Ores  which  receive  a  first  concentration  by  ascending 
waters  and  a  second  concentration  by  descending  waters.     The 
concentration    by  ascending  waters   may  wholly  precede  the 
concentration  by  descending  waters,  but    often  the  two  pro- 
cesses are  at  least  partly  contemporaneous.     The  materials  of 
class  (c)  comprise  oxides,  carbonates  and  chlorides  above  the 
level  of  groundwater,  and  rich  and  ppor  sulphurets,  tellurides, 
metallic  ores,    etc.,  below  the    level   of  groundwater.     At  or 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       429 

near  the  level  of  groundwater  these  two  kinds  of  products 
will  be  more  or  less  intermingled,  and  there  will  frequently  be 
a  transition  belt  of  considerable  breadth. 

How  extensive  are  the  deposits  of  class  (a)  I  shall  not  attempt 
to  state.  Indeed,  I  have  not  such  familiarity  with  ore-deposits 
as  to  entitle  me  to  an  opinion  upon  this  point.  However,  a 
considerable  number  of  important  ore-deposits  belong  to  this 
class.  This  class  is  illustrated  by  the  Lake  Superior  copper- 
deposits. 

The  ore-deposits  of  class  (b)  are  important.  Of  the  various 
ores  here  belonging,  probably  the  iron-ores  are  of  the  most 
consequence.  A  conspicuous  example  of  deposits  of  this  kind 
are  the  iron-ores  of  the  Lake  Superior  region. 

It  is  believed  that  the  ore-deposits  of  class  (c)  are  by  far  the 
most  numerous.  I  suspect  that  a  close  study  of  ore-deposits  in 
reference  to  their  origin  will  result  in  the  conclusion  that  the 
great  majority  of  ores  formed  by  underground  water  are  not 
the  deposits  of  ascending  waters  alone,  but  have  by  this  process 
undergone  a  first  concentration,  and  that  descending  waters 
have  produced  a  second  concentration,  as  a  result  of  which 
there  is  placed  in  the  upper  50  to  500  or  possibly  even  1000 
meters  of  an  ore-deposit  a  large  portion  of  the  metalliferous 
material  which  originally  had,  as  a  result  of  the  first  con- 
centration, a  much  wider  vertical  distribution. 

To  the  foregoing  classification  objections  will  at  once  occur. 
It  will  be  said  that  there  are  no  sharp  dividing  lines  between 
the  groups  and  classes.  To  this  objection  there  is  instant 
agreement.  Transitions  are  everywhere  the  law  of  nature. 
In  another  place*  I  have  explained  that  there  are  gradations 
between  different  classes  of  rocks,  and  this  statement  applies 
equally  well  to  ore-deposits.  I  even  hold  that  there  are  grada- 
tions between  ore-deposits  which  may  be  explained  wholly  by 
igneous  agencies,  and  those  which  may  be  explained  wholly  by 
the  work  of  underground  water,  or  by  processes  of  sedimenta- 
tion. Ore-deposits  which  have  received  a  first  concentration 
by  igneous  agencies  or  by  processes  of  sedimentation  are  sure 
to  be  reacted  upon  by  the  circulating  underground  waters,  and 
thus  a  second,  or  even  a  third  concentration  may  take  place. 

*  "The  Naming  of  Kocks,"  by  C.  K.  Van  Hise,  Journ.  of  GeoL,  vol.  vii.,  1899, 
pp.  687-688. 


430 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 


The  first  concentration  by  igneous  or  sedimentary  processes  may 
be  the  more  important  or  dominant  process,  or  the  additional 
concentration  or  concentrations  by  underground  waters  may  be 
the  more  important  or  dominant  processes.  In  some  cases, 
therefore,  the  ores  may  be  referred  to  as  produced  by  igneous 
agencies,  in  others  as  produced  by  processes  of  sedimentation, 
in  others  as  produced  by  these  in  conjunction  with  underground 
waters,  and  in  still  others  as  produced  mainly  by  underground 
waters.  Moreover,  there  will  be  found  to  be  undoubted  grada- 
tions between  the  different  classes  of  deposits  formed  by  under- 
ground waters.  Ore-deposits  which  are  precipitated  almost 
solely  by  ascending  waters  will  grade  into  those  in  which  de- 
scending waters  have  produced  an  important  effect,  and  thus 
there  will  be  transition  between  classes  (a)  and  (c).  Similarly 
there  will  be  every  gradation  between  classes  (a)  and  (b),  and 
between  classes  (b)  and  (c).  If  this  be  so  it  will  not  infre- 
quently happen  that  a  single  fissure  may  fall  partly  in  one 
class  and  partly  in  another.  Thus,  a  single  ore-deposit  may  be- 
long partly  in  class  (a)  and  partly  in  class  (c).  However,  in 
most  cases  a  deposit  will  primarily  belong  to  one  of  the  three 
classes.  Indeed,  not  only  are  there  gradations  between  different 
varieties  of  the  ore-deposits  among  themselves,  but  there  are 
gradations  between  the  ore-deposits  and  the  rocks,  for  the  ore- 
deposits,  in  many  cases,  are  not  sharply  separated  from  the 
country-rocks,  but  grade  into  them  in  various  ways. 

In  answer  to  the  above  objection  concerning  gradations,  it 
may  be  said  that  I  know  of  no  classification  of  ore-deposits 
which  has  yet  been  proposed  to  which  the  same  objection  may 
not  be  urged  with  equal  or  greater  force. 

However,  this  retort  does  not  give  any  criterion  by  which  the 
usefulness  of  the  above  classification  may  be  tested.  The  test 
is,  does  this  classification  give  us  a  more  satisfactory  method  of 
studying  ore-deposits  than  has  heretofore  been  possible  ?  Will 
an  attempt  to  apply  this  classification  assist  mining  engineers 
and  geologists  in  accurately  describing  ore-deposits  ?  Will  the 
classification,  to  a  greater  extent  than  any  previous  one,  give 
engineers  rules  to  guide  them  in  their  expenditure  in  explora- 
tion and  exploitation  ?  By  these  criteria  I  am  willing  that 
the  classification  shall  be  tested. 

As  an  illustration  of  the  practical  usefulness  of  the  classifica- 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       431 

tion,  is  the  connection  between  genesis  and  depth.  Where  the 
ores  are  deposited  by  ascending  waters  alone  it  has  been  pointed 
out  that  this  is  favorable  to  their  continuity  to  great  depth. 
Therefore,  where  a  given  ore-deposit  has  been  shown  to  belong 
to  this  class,  the  expenditure  of  money  for  deep  exploration  is 
warranted.  "Where  a  deposit  is  produced  by  descending  waters 
alone,  the  probable  extent  in  depth  is  much  more  limited.  In 
such  cases,  when  the  bottom  of  the  oxidized  product  is  reached, 
it  would  be  the  height  of  folly  to  expend  money  in  deep  ex- 
ploration. Where  the  ore-deposit  belongs  to  the  third  class, 
that  produced  by  ascending  and  descending  waters  combined, 
there  will  again  be  a  richer  upper  belt  which  we  cannot  hope 
will  be  duplicated  at  depth.  However,  this  class  of  deposits 
may  grade  into  first  class,  and  after  the  transition  the  deposit 
may  be  rich  enough  to  warrant  exploitation  at  depth ;  but  if 
such  work  be  undertaken  it  must  be  done  with  the  understand- 
ing that  the  rich  upper  products  peculiar  to  the  belt  of  weather- 
ing will  not  be  reduplicated  at  depth.  It,  therefore,  appears  to 
me  that  the  determination  to  which  of  the  classes  of  ore-de- 
posits produced  by  underground  waters  a  given  deposit  belongs 
has  a  direct  practical  bearing  upon  its  exploration  and  exploita- 
tion. 

It  is  my  hope  that  mining  engineers  and  geologists  will 
study  ore-deposits  in  various  regions  in  reference  to  the  prin- 
ciples discussed  in  this  paper.  It  appears  to  me  that  he  who 
does  this  will  be  capable  of  interpreting  better  than  before  the 
phenomena  which  he  finds  in  the  ore-body  or  bodies  with  which 
he  is  particularly  concerned.  Of  course,  it  is  fully  understood 
that  few  ore-deposits  will  illustrate  all  of  the  principles  above 
given.  It  is  appreciated  that  for  a  certain  ore-deposit  some 
few  of  the  principles  given  on  the  foregoing  pages  may  be  the 
dominating  ones,  and  that  others  are  unimportant.  But  this  is 
precisely  what  I  should  expect. 

In  addition  to  the  points  specially  emphasized  in  this  paper, 
accurate  descriptions  should  be  made  of  the  relations  of  the 
different  minerals  of  ore-deposits;  of  the  occurrence  of  each 
mineral  with  reference  to  the  wall-rocks ;  and  their  variations 
in  composition,  relations  and  richness  at  various  depths,  reckon- 
ing both  above  and  below  the  level  of  groundwater.  More- 
over, such  a  study  should  include  close  observation  of  the 


432          THE    SECONDARY   ENRICHMENT    OF    ORE-DEPOSITS. 

gangue-minerals  in  their  relations  to  one  another  and  to  the 
valuable  minerals ;  for  in  many  instances  they  may  give  impor- 
tant testimony  as  to  the  origin  of  the  ore-deposit.  In  this 
paper,  the  gangue-minerals  have  been  altogether  ignored. 
Furthermore,  a  study  should  be  made  of  the  changes  of  country- 
rocks  and  wall-rocks.  "When  a  comprehensive  study  of  various 
ore-bearing  districts  has  been  made,  including  all  of  these  fac- 
tors, and  the  special  factors  discussed  on  pp.  393-421,  it  is  be- 
lieved that  a  more  satisfactory  treatise  upon  ore-deposits  may 
be  written  than  has  yet  appeared. 

Such  a  study  of  ore-deposits  must  be  a  difficult  one,  involving 
as  it  does,  a  working  knowledge  of  petrography,  of  mineralogy, 
and  of  modern  physical  chemistry.  Undoubtedly,  the  story  of 
many  ore-deposits  will  be  found  to  be  exceedingly  complex,  and 
not  to  come  fully  within  the  scope  of  the  principles  discussed 
in  this  paper.  So  far  as  any  ore-deposit  fails  to  do  this,  it  will 
give  us  data  upon  which  to  state  a  more  nearly  complete  theory 
of  ore-deposits  than  that  here  proposed. 


THE   SECONDARY   ENRICHMENT    OF    ORE-DEPOSITS.  433 


The  Secondary  Enrichment  of  Ore-Deposits.* 

BY  S.    F.    EMMONS,    WASHINGTON,   D.  C. 

(Washington  Meeting,  February,  1900.) 

IT  was  said  by  many  who  discussed  Professor  Posepny's 
admirable  paper  on  the  "  Genesis  of  Ore-Deposits,"  read  at  the 
Chicago  meeting  of  the  Institute,  in  1893,  that  its  most  valu- 
able feature  was  the  clear  distinction  which  it  drew  between 
the  influence  upon  ore-deposits  of  the  "  vadose  "  circulation  of 
waters  descending  directly  from  the  surface,  and  that  of  the  deep 
underground  circulation  of  waters  generally  coming  from  the 
depths,  and  assumed  by  the  author  to  be  ascending  through 
more  or  less  open  spaces  under  the  influence  of  heat.  A  little 
later  the  effect  of  the  oxidizing  action  of  the  vadose  circulation 
upon  ore-deposits  was  ably  and  exhaustively  treated  by  Prof. 
R.  A.  F.  Penrose,  in  a  paper  on  "  The  Superficial  Alteration  of 
Ore-Deposits  "f — the  only  one,  so  far  as  I  know,  which  has 
been  exclusively  devoted  to  this  important  subject. 

My  own  first  detailed  study  of  ore-deposits  was  made  at 
Leadville,  in  1880,  at  a  time  when  almost  the  only  minerals 
visible  in  those  deposits  were  in  oxidized  forms.  That  this 
form  was  the  result  of  the  alteration  of  earlier  sulphides  by 
surface-waters  had  to  be  proved  at  the  time  by  induction  or 
analogy,  the  general  correctness  of  which  was,  however,  abund- 
antly confirmed  by  subsequent  developments.  Thus  I  was 
early  impressed  with  the  importance  of  distinguishing,  in  the 
study  of  an  ore-deposit,  the  alteration-products,  resulting  from 
the  action  of  oxidizing  waters  descending  from  the  present 
surface,  from  the  earlier-formed  sulphides ;  and,  assuming  that 
the  latter  were  primary  or  original,  I  called  the  former  sec- 
ondary. I  also  went  so  far  as  to  sayj  with  regard  to  oxidized 
ores  passing  into  sulphides  in  depth : 

"So  generally  is  this  accepted  as  a  rule  in  ore-deposits  that  it  would  require 
special  demonstration  to  prove  beyond  a  doubt  that  the  native  metals  or  their 


*  Published  by  permission  of  the  Director  of  the  U.  S.  Geological  Survey, 
t  Jmir.  GeoL,  vol.  ii.,  April-May,  1894,  pp.  288-317. 
j  U.  S.  Geol.  Sur.t  Mon.  xii.,  p.  562. 


434  THE   SECONDARY   ENEICHMENT   OF   ORE-DEPOSITS. 

oxides  and  chlorides  (except  perhaps  gold,  tin,  and  the  platinum  group  of  metals) 
are,  in  any  particular  case,  original,  and  not  the  result  of  secondary  alteration 
from  sulphides. ' ' 

Admitting  fully  the  general  truth  of  the  statement  that  the 
descending  surface-waters  exert  an  oxidizing  action,  and  hence 
that  oxidation-products  within  the  reach  of  surface-waters  are 
the  result  of  alteration  by  the  latter,  I  have  heen  led  to  believe, 
hy  observations  now  extending  over  a  considerable  number  of 
years,  that,  under  favorable  conditions,  the  oxidation-products 
may  be  changed  back  again  into  sulphides  and  redeposited  as 
such,  thus  producing  what  may  be  called  a  sulphide-enrich- 
ment of  the  original  deposits.  Penrose,  perhaps,  admits  this 
when  he  says  that  "  the  action  of  surface  influences  is,  in  rare 
cases,  one  of  reduction,  which,  however,  often  follows  a  pre- 
vious oxidation;"  but  he  gives  no  instances,  and  apparently 
has  in  mind  only  those  cases  in  which  oxides  are  reduced  to 
sulphides  in  the  presence  of  organic  matter.  Posepny,  on  the 
other  hand,  strong  in  the  conviction  of  the  correctness  of  his 
theoretical  views,  does  not  recognize  any  exceptions  to  the 
general  rule.  With  him,  apparently,  the  fact  that  a  deposit 
consists  of  sulphides  is  sufficient  proof  that  it  has  been  made 
by  the  ascending  currents  of  a  deep  underground  circulation, 
and  cannot  have  been  made  by  vadose  or  descending  waters. 
Being  rather  a  searcher  after  facts  than  a  theorist,  I  am  not 
deterred  from  accepting  what  may  appear  to  me  the  correct 
reading  of  observed  facts  because  it  seems  to  contradict  gener- 
ally accepted  theories. 

In  geological  observation,  however,  especially  underground, 
where  the  field  is  often  very  limited,  it  is  not  always  possible 
to  be  certain  of  the  correctness  of  one's  interpretation  of  a  given 
phenomenon,  especially  when  one  is  confined  to  a  single  dis- 
trict or  group  of  mines.  Another  observer  might  construe  the 
evidence  otherwise.  It  is  only  by  multiplying  observations  in 
'different  and  widely  separated  localities,  and  by  finding  in  all 
the  same  sequence  of  phenomena,  to  which  the  same  interpreta- 
tion applies,  that  one  arrives  in  time  at  what  may  be  considered, 
from  a  geological  standpoint,  a  reasonably  certain  conclusion. 

In  the  present  case,  I  could  have  wished  to  multiply  my 
observations  much  further,  and  to  obtain  more  light  upon  the 
probable  chemical  processes  involved  than  I  have  as  yet  been 


THE    SECONDARY   ENRICHMENT    OP   ORE-DEPOSITS.  435 

able  to  find  in  chemical  literature,  before  committing  myself 
to  a  public  statement  with  regard  to  them.  I  have  hoped, 
moreover,  to  have  some  experimental  chemical  work  carried 
on  upon  lines  suggested  by  my  observations  in  the  laboratory 
of  the  U.  S.  Geological  Survey;  but  the  limited  force  and 
space  available  for  such  work  have  rendered  it  thus  far  imprac- 
ticable. 

I  find,  however,  among  many  mining  engineers  an  increas- 
ing conviction  that  the  rich  concentrations  found  in  many  de- 
posits of  both  copper-  and  silver-ores,  are  the  results  of  secondary 
enrichment.  Moreover,  Mr.  Walter  H.  Weed,  who  was  asso- 
ciated with  me  in  the  geological  study  of  the  Butte  region  in 
1896,  and,  during  the  summer  of  1899,  in  underground  work 
there,  submitted  at  the  recent  meeting  of  the  Geological  Society 
of  America,  an  article  on  the  "  Enrichment  of  Mineral  Veins 
by  Later  Metallic  Sulphides,"*  which  contains  much  that  I  had 
intended  to  write  on  the  subject.  Hence,  I  feel  it  necessary, 
in  self-defense,  to  publish  something  in  the  nature  of  a  caveat, 
to  show  that  my  attention  has  been  directed  to  this  subject  for 
some  time  past,  even  though  the  evidence  for  the  conclusions 
I  have  reached  is  not  yet  as  complete  as  I  could  wish. 

PREMISES  OF  BELIEF. 

To  avoid  misunderstanding  it  may  be  well  to  state,  at  the  out- 
set/ the  premises  of  my  belief.  In  the  first  place,  I  eliminate 
from  this  discussion  the  ore-deposits  formed  exclusively  by 
magmatic  differentiation,  and  first  brought  into  prominence  by 
the  Scandinavian  geologist  Yogt — not  that  I  deny  the  import- 
ance of  this  mode  of  ore-concentration  as  a  possible  first  cause, 
but  because,  in  my  20  years'  study  of  ore-deposits,  I  have  not 
yet  had  an  opportunity,  as  I  have  elsewhere  stated, f  of  seeing 
any  which  were  not  due,  in  the  condition  in  which  they  now 
exist,  "  to  further  concentration,  perhaps  many  times  repeated." 
Hence,  I  assume  that  the  majority  of  ore-deposits,  as  at 
present  found,  owe  their  existence  to  the  agency  of  circulating 
waters ;  and  it  is  of  these  only  that  I  speak  in  this  paper. 

Circulating  Waters  of  Surface-Origin. — I  am  inclined  to  limit 
my  subject  further  by  excluding  those  water-formed  deposits, 

*  Bull.  Geol.  Soc.  Am.,  vol.  xi.,  1900,  pp.  179-206. 
t  This  volume,  p.  201. 

28 


436  THE    SECONDARY    ENRICHMENT    OF    ORE-DEPOSITS. 

which,  according  to  the  theory  of  some  French  geologists,  have 
been  deposits  from  solution  in  waters  originating  or  occluded 
in  igneous  magmas,  or,  as  the  Scandinavian  geologists  express 
it,  by  pneumatolysis,  since  such  waters  cannot  have  formed  an 
essential  part  of  the  circulation,  properly  speaking. 

I  have  found  no  reason  to  change  essentially  my  early  belief 
that  the  waters  which  have  been  the  principal  agents  in  form- 
ing ore-deposits  came  originally  from  the  surface.  As  I  then 
expressed  it:* 

"There  are,  therefore,  both  upward  and  downward  currents;  it  being  gen- 
erally assumed  that  the  latter  are  surface-waters  sinking  under  the  influence  of 
gravity,  and  the  former,  the  same  waters  rising  under  that  of  the  internal  heat  of 
the  earth." 

Bickard  uses  a  very  suggestive,  though  homely  metaphor, 
to  illustrate  the  manner  of  this  circulation,  when  he  says  :f 

"We  may  compare  the  circulation  of  water  up  and  down  through  the  earth's 
rocky  exterior,  to  that  of  the  ordinary  heater  in  a  house.  The  water  circulates, 
because,  when  hot,  it  rises  through  the  length  of  pipe,  and,  when  cool,  it  falls 
back  to  be  reheated." 

It  is  the  difference  of  temperature  produced  by  internal  heat 
that  causes  the  water  to  rise,  though  gravity  is  still  the  impel- 
ling force,  since  the  colder  surface-water  is  descending  to  take 
the  place  of  that  which  rises.  Only  occluded  water  could  find 
its  motive  power,  independently  of  gravity,  in  the  rock-mass 
in  which  it  originated. 

Grroundwater- Level. — Posepny,  as  I  have  already  remarked, 
has  strongly  emphasized  the  distinction  between  the  vadose  or 
descending  circulation  and  the  profound  or  ascending  circula- 
tion, the  separating  line  between  which  is  called  the  ground- 
water-level.  Lest  my  statement  'that  he  did  not  recognize  the 
formation  of  sulphides  by  the  vadose  circulation  may  be 
deemed  too  sweeping,  I  will  quote  (not  finding  a  direct  decla- 
ration on  this  point  from  him)  Dr.  Raymond's  exposition  of  his 
meaningij 

"2.  Concerning  the  condition  (the  vadose  circulation  above  groundwater- 
level)  which  is  most  open  to  our  observation,  we  know  a  great  deal.  We  know, 
for  instance,  from  an  overwhelming  number  of  observations,  that  the  solutions  of 

*  U.  S.  Geol.  Sur.,  Mon.  xii.,  p.  570. 

f  This  volume,  p.  220.  $  This  volume,  p.  254. 


THE    SECONDARY   ENRICHMENT    OP   ORE-DEPOSITS.  437 

the  vadose  circulation  are  oxidizing,  and  that  (apart  from  the,  probably  rare, 
reformation  of  sulphides  by  the  action  of  organic  matter)  they  do  not  precipitate 
sulphides,  but,  on  the  contrary,  attack  and  decompose  them." 

It  is  evident  from  Posepny's  remarks  on  different  deposits 
(e.g.,  those  ofWiesloch,  in  Baden*),  that  this  is  a  correct  presen- 
tation of  his  views.  While  this  distinction  of  Posepny  has  been 
very  useful,  undoubtedly  giving  to  many  students  a  clearer  con- 
ception of  the  relative  influence  of  waters  descending  from  the 
surface,  and  those  arising  from  the  depths,  I  believe  that  in  this, 
as  in  most  geological  generalizations,  the  lines  should  not  be 
drawn  too  strictly,  but  must  be  susceptible  to  considerable  modi- 
fication under  varying  conditions.  Inasmuch  as  both  ascending 
and  descending  currents  are  part  of  the  same  general  circulation, 
there  must  also  be  a  vast  amount  of  nearly  horizontal  or  lateral 
movement.  Moreover,  in  our  western  mountain-regions  the 
groundwater-level  is  not,  so  far  as  my  experience  goes,  the 
definite  horizon  predicated  by  Posepny,  which  bears  a  compara- 
tively uniform  relation  to  the  existing  surface ;  nor  is  the  oxi- 
dizing influence  of  surface-waters  always  strictly  confined  to 
the  region  above  it. 

Yery  early  in  my  studies  of  ore-deposits,  in  writing  on  a 
typical  instance  of  the  secondary  alteration  of  ore-deposits,  I 
defined  the  groundwater-level  thus  :f 

"The  permanent  water-level  at  any  point  beneath  the  earth's  crust,  and  within 
the  range  of  human  observation,  is  evidently  that  level  to  which  water  will  rise 
by  the  filling  of  a  hydrostatic  basin  (which  may  consist  of  any  system  of  channels 
permitting  its  ready  circulation,  such  as  joints,  fissures,  bedding-planes  or  porous 
rocks)  up  to  the  point  of  its  overflow,  or  where  it  would  drain  out  either  to  the 
surface  or  into  another  hydrostatic  basin.  The  water  filling  such  basins  is  orig- 
inally supplied  from  the  surface,  but  after  a  comparatively  long  passage  through 
the  rocks,  during  which  its  oxidizing  agencies,  such  as  air,  organic  acids,  etc., 
may  be  supposed  to  have  become  neutralized,  or  to  have  exhausted  their  power 
upon  the  rocks  through  which  they  have  passed.  The  water  or  moisture  which 
furnishes  the  active  agencies  of  secondary  decomposition  of  ore-bodies  must,  on 
the  other  hand,  come  to  them  directly  from  the  surface,  and  not  be  neutralized  by 
a  long  passage  through  rock-material,  or  by  mingling  with  a  large  body  of  already 
neutralized  water,  such  as  that  which  exists  below  the  water-level.  This  seems  to 
me  to  be  the  explanation  of  the  fact  that  surface-waters  act  as  oxidizing  agents 
above  water-level,  and  as  a  protection  against  such  action  below  the  water  level." 

Since  then,  I  have  observed  many  instances  in  which  the 

*  This  vol.,  p.  69. 

t  Proc.  Colo.  Sci.  Soc.,  vol.  ii.,  Part  II.,  p.  102.     1886. 


438  THE    SECONDARY    ENRICHMENT    OF    ORE-DEPOSITS. 

zone  of  oxidation,  as  defined  by  the  water-level,  is  not  a  gen- 
erally even  surface,  more  or  less  conformable  to  the  surface  of 
the  ground.  The  most  striking  that  I  recall  now,  is  in  the 
Tintic  district  of  Utah,  where,  in  the  deposits  in  the  limestones, 
the  limit  of  oxidation  had  not  been  reached  at  1600  ft.  below 
the  surface,  while,  in  veins  in  the  igneous  rocks,  scarce  half 
a  mile  away,  the  groundwater-level  and  zone  of  unaltered 
sulphides  were  met  within  200  to  300  ft.  of  the  surface. 

Deposition  of  Oxides  below  Water-Level. — Winchell  calls  atten- 
tion to  a  striking  instance  of  oxidizing  action  extending  below 
the  groundwater-level  when  in  his  discussion*  of  Posepny's 
paper  he  speaks  of  the  Lake  Superior  iron-ore  deposits : 

11  The  ore-lenses  lie  in  basins  of  greenstone  schists  or  other  rocks,  and  occur  at 
various  depths  to  at  least  2000  feet.  At  the  lower  edges  of  some  of  these 
lenses  are  found  deposits  of  silica,  kaolin,  etc.,  which  have  plainly  been  removed 
from  the  ore-body  above  in  process  of  concentration.  This  is  much  below  the 
vadose  circulation,  as  the  immense  pumping-engines  and  the  rivers  of  water  which 
they  throw  the  year  round  testify  ;  but  it  is  an  instance  of  the  formation  of  ore- 
deposits  on  the  largest  scale  by  descending  waters. ' ' 

In  my  own  experience,  I  have  met  many  instances  of  oxidiz- 
ing action  below  the  groundwater-level,  but  nothing  on  the 
scale  of  these  Lake  Superior  deposits.  They  were  generally 
very  local  in  their  development,  and  I  have  been  accustomed 
to  look,  with  more  or  less  success,  for  their  cause  in  a  recently 
formed  water-channel  down  which  the  surface-waters  were  able 
to  descend  freely  and  with  relative  rapidity. 

It  is  not,  however,  the  oxidizing  action  of  surface-water  that 
is  in  question  here,  though  that  process  is  highly  interesting, 
and  has  had  great  influence  upon  the  relative  richness  of  ore- 
bodies.  Moreover,  notwithstanding  our  pretty  clear  compre- 
hension of  it,  many  new  data  might  be  cited  concerning  it. 
But  the  question  under  discussion  is,  to  what  extent  sulphides 
may  be  deposited  from  descending  surface-waters,  and  under 
what  conditions. 

Deposition  of  Sulphides. — Prior  to  my  studies  at  Butte  in 
1896,  I  am  free  to  confess,  I  had  not  given  much  thought  to 
the  possible  deposition  of  sulphides  from  surface-waters.  The 
fact  that,  in  the  presence  of  organic  matter,  oxides  may  be 
reduced  to  sulphides  was  of  course  well  known ;  and  the  few 

*  This  volume,  p.  229. 


THE   SECONDARY   ENRICHMENT   OF   ORE-DEPOSITS.  439 

instances  of  the  formation  of  pyrite  in  this  manner  that  came 
under  my  observation,  were  noted  as  curiosities  rather  than  as 
matters  of  economic  importance.  The  sulphides  that  I  found 
within  the  oxidized  zone  and  distinctly  above  the  groundwater- 
level  (mostly  small  masses  of  galena  and  pyrite,  but  in  some 
cases  very  considerable  bodies  of  the  latter)  were  generally 
explainable  as  material  so  dense  that  oxidizing  waters  had  not 
yet  penetrated  into  the  interior  of  the  mass,  and  were,  to  my 
mind,  simply  an  additional  proof  that  the  groundwater-level 
was  not  an  absolute  'line  of  division  between  oxides  and  sul- 
phides, but  that  under  favorable  physical  conditions  the  latter 
might  exist  above  it,  as  the  former  could  extend  below  it. 
There  were,  it  is  true,  occasional  occurrences  that  could  not  be 
explained  on  the  ground  of  imperfect  oxidation  through  physi- 
cal obstacles ;  and  these  were  stored  in  my  memory,  until  suf- 
ficient evidence  should  have  accumulated  to  indicate  some 
general  explanation.  Of  such  was  the  observation  made  during 
my  Leadville  work,*  that,  in  the  kernels  of  partially  altered 
galena  surrounded  by  a  crust  of  cerussite,  which  were  found  in 
the  oxidized  zone,  the  galena  was  abnormally  rich  in  silver, 
containing  more  than  five  times  as  much  as  did  the  cerussite 
resulting  from  its  alteration,  the  tenor  of  silver  in  which  was 
nearer  to  the  normal  or  average  proportion. 

In  the  same  way,  according  to  Blow,f  "  the  small  seams  found 
penetrating  the  limestone  at  the  bottom  of  the  ore-body  are 
often  formed  of  galena-ore,  and  are  always  richer  than  the  lead- 
sand  and  cerussite-ore  above."  In  these  cases  it  is  evident 
that  the  action  of  the  surface-waters  has  been  to  concentrate  the 
silver  in  the  sulphide-ore,  not  in  the  oxidized  product. 

Again,  the  oxidized  ores  observable  at  the  time  of  my  study 
of  the  Leadville  deposits  carried  abundant  iron,  lead  and  silver, 
but  scarcely  a  trace  of  zinc ;  yet  it  was  assumed,  and  soon  found 
to  be  the  fact,  that  the  sulphide-ores  consisted  of  mixtures  of 
pyrite,  galena  and  zinc-blende,  the  latter  in  fairly  equal  amount. 
The  far  greater  solubility  of  the  zinc-salts,  over  those  of  lead, 
would  account  for  the  latter's  remaining  to  a  great  extent  in  their 
original  position ;  but  the  question  was,  what  had  become  of  the 
zinc  ?  Mining  in  the  sulphide-bodies  in  later  years  has  shown 

*  U.  S.  Geol.  Sur.,  Mon.  xii.,  p.  553.  t  Trans.,  xviii.,  169. 


440  THE    SECONDARY   ENRICHMENT   OF   ORE-DEPOSITS. 

that,  immediately  below  the  zone  of  oxidation,  the  bodies  of 
mixed  sulphides  are  far  richer  in  zinc-blende  than  the  average 
of  those  enormous  bodies  mined  at  greater  depths.  Blow,  as 
a  result  of  his  nine  years'  work  in  the  ore-bodies  of  Iron  Hill, 
draws  the  following  conclusion  from  these  facts  :* 

"  It  seems  probable  that  a  large  proportion  of  the  zinc,  which  was  totally  re- 
moved from  the  carbonate  ores,  has  been  redeposited  as  a  sulphide,  and  princi- 
pally just  below  the  line  of  complete  oxidation,  by  surface-waters,  and  such  rede- 
position  has  advanced  and  increased  pari  passu  with  the  limit  and  extent  of  such 
oxidizing  action." 

There  are  many  other  instances  in  which  suggestive  remarks 
have  been  made  upon  the  probable  deposition  of  sulphides  by 
descending  surface-waters,  as  will  be  shown  later.  Most  per- 
tinent at  the  present  moment  is  that  made  by  our  President, 
Dr.  James  Douglas,  in  1890, f  with  regard  to  the  Butte  cop- 
per-mines. In  speaking  of  the  vertical  distribution  of  the 
various  kinds  of  ore,  he  says  : 

' '  It  seems  as  if  the  copper,  leached  out  of  the  four  hundred  feet  of  depleted 
vein,  had  been  concentrated  in  the  underlying  ore,  and  had  thus  produced  a  zone 
of  secondary  ore  about  two  hundred  feet  deep,  which  contains,  as  might  be  ex- 
pected, about  thrice  its  normal  copper  contents. " 

Such  suggestions  as  these  are  useful,  however,  rather  as 
confirmatory  data,  and  hardly  form  a  sufficient  basis  on  which 
to  found  any  definite  generalization  or  theory.  For  this,  one 
needs  to  have  the  results  of  a  systematic  study  of  an  important 
district,  based  on  accurate  and  detailed  maps,  on  which  the 
underground  observations  are  worked  out  with  the  aid  of  care- 
ful microscopic  and  chemical  examinations  of  the  material 
gathered. 

INSTANCES  OF  SECONDARY  ENRICHMENT. 

It  was  during  the  study,  in  1896,  of  the  Butte  district,  and 
especially  of  its  copper-bearing  veins,  that  such  definite  evi- 
dence of  the  secondary  enrichment  of  sulphides  on  a  consider- 
able scale  was  first  obtained  by  me. 

Conditions  at  Butte. — The  following  is  a  brief  statement  of  the 
conditions  which  presented  themselves  as  a  result  of  these 
studies  at  Butte.  There  is  evidence  in  this  district  of  several 

*  Trans.,  xviii.,  172.  f  Trans.,  xix.,  693. 


THE    SECONDARY    ENRICHMENT    OF    ORE-DEPOSITS.  441 

successive  rock-fracturing  movements.  In  regard  to  the  earlier 
movements  which  produced  the  primary  sulphide-deposition 
it  is  not  always  possible  to  differentiate  clearly  one  from  the 
other  in  point  of  time.  It  is,  however,  possible  to  distinguish 
another  set  of  fractures,  which  I  have  called  secondary*  or 
post-mineral  fractures,  because  they  are  distinctly  later  than 
the  original  deposition  of  sulphides,  since  the  fissures  contain 
within  them  dragged-in  and  more  or  less  rounded  fragments 
of  these  sulphides  together  with  quartz  and  country-rock. 

There  are  two  sets  of  secondary  fractures  or  faults  :  first, 
those  which  run  east  and  west,  and  are  generally  parallel  to 
and  more  or  less  coincident  with  the  original  east  and  west 
vein-systems,  which  I  have  called  "  strike  faults ;"  and,  second, 
the  transverse  fractures  or  cross-faults  which  strike  between 
northwest  and  northeast,  and  have,  as  a  rule,  a  shallower  dip 
than  the  east  and  west  fractures.  The  second  class  have  caused 
an  evident  displacement  of  the  veins,  sometimes  amounting  to 
several  hundred  feet.  Whether  the  first  have  been  accom- 
panied by  any  considerable  movement  of  displacement  cannot 
be  determined  on  account  of  their  parallelism  to  the  veins. 
No  definite  proof  has  yet  been  found  to  determine  whether  the 
two  systems  of  fractures  were  formed  contemporaneously  or 
not ;  my  general  impression  has  been  that  the  shattering  of 
the  country  was  produced  by  successive  dynamic  shocks  of 
increasing  intensity,  which  first  formed  fractures  along  the 
lines  of  the  existing  vein-systems,  with  slight  movements  of 
displacement  and  consequent  shattering  and  grinding  of  the 
material  traversed,  and  finally  resulted  in  a  cross-fracturing 
accompanied  by  a  certain  amount  of  lateral  displacement  of 
veins.  The  strike-fractures  or  faults,  which,  in  the  nature  of 
things,  are  the  most  open  to  observation,  being  constantly  ex- 
posed by  the  mine  drifts,  vary  in  size  from  thin  clay-selvages 

*  My  use  of  the  word  "secondary"  in  this  connection  has  been  criticised  as 
liable  to  misconstruction,  because  it  has  hitherto  been  used  to  designate  the  altera- 
tion by  surface-waters,  and  applied  exclusively  to  oxidized  forms  of  mineral-de- 
position. It  is  further  said  that  one  has  no  right  to  assume  that  only  one  frac- 
turing and  ore-deposition  has  preceded  those  thus  designated  "  secondary. "  While 
admitting  the  force  of  these  criticisms,  I  have  been  unable  to  find  another  satis- 
factory word,  because  I  am  not  yet  sure  in  my  own  mind  that  all  the  successive 
processes  that  have  taken  place  in  these  deposits  are  known,  and  having  com- 
mitted myself  to  the  use  of  this  word  in  print,  think  it  best  to  continue  it  until 
our  knowledge  is  more  complete. 


442  THE    SECONDARY   ENRICHMENT    OF   ORE-DEPOSITS. 

to  broad  breccia-zones  up  to  15  or  20  feet  thick,  but  are  most 
commonly  seams  a  few  inches  thick  carrying  small  rolled 
fragments  of  granite,  quartz  and  ore  in  a  soft,  wet  kaolin-mud. 
They  are  found  in  foot-  or  hanging-wall,  or  within  the  vein 
itself,  often  several  to  a  given  cross-section,  and  extend  in  depth 
as  far  as  the  explorations  have  yet  reached.  Except  in  the  case 
of  a  few  breccia-zones  within  an  original  vein-system  they  do 
not  ordinarily  carry  pay-ore. 

The  cross-fractures  or  faults  have  been  quite  extensively  de- 
veloped since  our  field-work  was  completed  as  the  result  of  the 
many  law-suits  that  have  sprung  up  in  the  district,  and  have 
been  carefully  studied  by  the  many  experts  engaged  in  investi- 
gating the  geological  conditions  bearing  upon  the  different 
questions  in  dispute.  In  some  cases  they  are  known  only  as 
planes  of  movement  cutting  off  the  veins;  in  others,  they  have 
been  found  to  contain  so  much  dragged-in  ore  from  the  various 
veins  they  cross,  as  to  constitute  valuable  ore-bodies.  In  the 
opinion  of  some  of  the  experts,  they  also  contain  considerable 
newly-deposited  ore  in  the  sulphide  form.  This,  I  have  not  yet 
had  an  opportunity  of  verifying  from  personal  observation. 

Paragenetical  study  of  the  ore-deposits  shows  that  the  earli- 
est-formed minerals  are  quartz,  pyrite,  chalcopyrite  and  enar- 
gite.  Enargite  is  in  some  cases  later  than  chalcopyrite.  Veins 
composed  mainly  of  enargite  have  been  found  cutting  the  sil- 
iceous pyritic  veins.  The  richer  sulphides,  bornite,  chalcocite 
and  covellite,  which,  with  enargite,  constitute  the  most  valuable 
ores  of  the  middle  levels  of  most  of  the  mines,  are  of  later 
origin,  their  order  of  deposition  being,  as  far  as  microscopic 
observations  enabled  us  to  determine,  that  in  which  they  are 
named.  Little  opportunity  was  had  of  studying  the  oxides  and 
carbonates  of  copper  which  are  characteristic  of  the  zone  of 
oxidation,  and  would  normally  be  considered  of  an  entirely 
later  formation. 

The  prominent  characteristics  of  the  Butte  copper-lodes  are,' 
first,  an  upper  oxidized  zone  extending  down  from  200  to  400 
feet  from  the  surface  which  contains  less  than  1  per  cent,  of 
copper  on  the  average,  the  value  being  principally  in  silver. 
It  is  a  mass  of  crumbly,  honeycombed  quartz,  singularly  free 
from  metallic  oxides  when  one  considers  the  great  mass  of  the 
original  sulphides  found  in  the  veins  in  depth.  Second,  below 


THE   SECONDARY   ENRICHMENT   OF   ORE-DEPOSITS.  443 

this  is  a  rather  ill-defined  zone  characterized  by  great  values  in 
the  rich  copper  sulphides,  bornite  and  chalcocite  or  copper- 
glance,  associated  with  pyrite  and  chalcopyrite.  The  propor- 
tion of  these  rich  sulphides  gradually  decreases  with  depths 
until  in  some  mines  the  ores  consist  only  of  pyrite  with  a  slight 
admixture  of  chalcopyrite.  Enormous  amounts  of  copper-glance 
were  found  in  many  of  the  mines ;  generally  in  the  upper  levels 
of  the  sulphide  zone.  Sometimes  they  constituted  solid  masses 
fifteen  feet  or  more  in  thickness,  in  which,  however,  close  ex- 
amination showed  a  sprinkling  of  chalcopyrite  or  pyrite  in 
minute,  irregular,  and  often  pitted  grains  throughout  the  mass 
of  the  glance ;  not  infrequently  the  cleavage  faces  are  coated 
with  very  thin  films  of  native-silver. 

The  fact  that  struck  me  most  forcibly  with  regard  to  the  rich 
bodies  of  glance,  was  that  one  or  more  secondary  fractures  are 
invariably  found  in  their  immediate  neighborhood,  though  not 
necessarily  in  direct  contact  with  them.  In  a  few  instances,  at 
depths  of  a  thousand  feet  or  more,  considerable  bodies  of  the 
richer  sulphides  were  found  within  a  breccia  .zone.  The  largest 
masses  of  the  comparatively  rare  mineral,  covellite,  were  found 
on  the  1100-foot  level  of  the  East  Gray  Rock  mine  lying  in  a 
mass  of  breccia,  with  a  kaolinized  clay  matrix  so  soft  that  it 
would  run  when  opened.  In  the  comparatively  solid  veins, 
however,  glance  is  generally  found  as  a  streak  a  few  inches  to 
a  foot  or  more  in  width,  grading  oif  into  siliceous  pyritous  ore, 
with  a  thin  secondary  seam  near  it,  sometimes  in  foot-  or  hang- 
ing-wall, more  often  in  the  vein-material  itself.  This  is  rather 
a  bald  statement  of  the  leading  facts  which  led  me  to  the  con- 
clusion that  there  is  a  genetic  connection  between  the  second- 
ary fractures  and  the  rich  copper  sulphides;  a  conclusion  that 
is  confirmed,  so  far  as  I  know,  by  all  geologists  who  have  had 
opportunities  of  studying  these  veins.  It  is  generally  agreed 
that  most  of  these  sulphides  are  enrichments  of  the  earlier 
vein-deposits  by  solutions  that  followed  the  water-channels  af- 
forded by  some  of  the  secondary  fractures. 

The  next  question  that  presents  itself  is,  whether  this  enrich- 
ment was  produced  by  vadose,  or  by  deep  underground-waters ; 
in  other  words,  from  waters  that  have  been  descending  through 
the  oxidized  portions  of  the  lode,  or  from  a  new  set  of  ascend- 
ing currents  acting  since  the  secondary  fractures  were  formed. 


444  THE    SECONDARY   ENRICHMENT    OF    ORE-DEPOSITS. 

Although,  at  the  time  of  the  publication  of  the  Butte  Folio, 
there  were  many  facts  that  pointed  to  the  former  conclusion,  I 
hesitated  to  give  a  decided  opinion  on  the  question ;  first,  be- 
cause of  the  unfavorable  influence  it  might  have  on  mining  in 
general,  and  copper  mining  in  particular,  especially  in  this  im- 
portant district  (for  some  might  be  led  at  once  to  adopt  the 
conclusion  that  the  rich  sulphides  would  not  be  found  in  depth 
beyond  the  reach  of  such  descending  currents) ;  and  in  the 
second  place,  I  wished  to  accumulate  more  knowledge  myself 
before  propounding  a  theory  so  distinctly  opposed  to  that  gen- 
erally received. 

The  deposits  of  Butte  are  exceptional,  so  far  as  my  expe- 
rience goes,  in  the  depth  to  which  the  richer  copper  sulphides 
have  been  found  to  extend ;  for,  though  not  forming  the  large 
bodies  they  did  at  200  to  400  feet  below  the  water-level,  they 
are  still  found  here  and  there  at  1500  feet  or  more  below  this 
level,  though  in  apparently  decreasing  amount  as  compared 
with  the  immense  thickness  of  pyritous  ore. 

It  should  be  noted  in  this  connection,  however,  that  there  is 
evidence  that  the  groundwater-level  was  once  very  much 
lower  than  it  is  at  the  present  day.  It  is  proved  quite  con- 
clusively by  Mr.  Weed's  surface  studies  of  the  region  that  the 
granite  hills  to  the  east  of  Butte,  known  as  "  East  Ridge,"  and 
which  rise  abruptly  about  2000  feet  above  Meaderville  in  the 
valley  of  Silver  Bow  creek,  owe  their  present  elevation  to  a 
north  and  south  faulting  along  their  steep  western  face.  The 
evidence  of  faulting  and  consequent  relative  change  of  level  be- 
tween the  area  in  which  the  mines  occur  and  the  adjoining 
East  Ridge  is  mainly  derived  from  the  physiography  of  the 
region  beyond  the  latter  to  the  eastward;  but  it  is  confirmed 
by  the  discovery,  through  mine-shafts,  that  the  actual  rock- 
bottom  of  the  Meaderville  portion  of  Silver  Bow  valley  slopes 
downward  nearly  to  the  foot  of  the  steep  western  slope  of  the 
ridge,  reaching  a  depth  of  300  to  400  feet  below  the  surface  of 
the  present  valley  opposite  Meaderville,  and  probably  a  still 
greater  depth  further  south.  This  old  depression,  which  seems 
independent  of  present  drainage-systems,  is  now  filled  up  by 
talus  from  the  East  ridge.  Its  rock-surface  was  once  probably 
higher  than  the  eastern  face  of  the  East  ridge,  and  formed  a 
continuous  slope  with  it,  although  the  actual  date  and  the 


THE    SECONDARY    ENRICHMENT    OF    ORE-DEPOSITS.  445 

amount  of  the  displacement  caused  by  the  faulting  cannot  be 
accurately  determined.  It  must  have  occurred  in  compara- 
tively recent  time,  geologically  speaking,  and  have  caused  a 
raising  of  the  water-level  in  the  depressed  region,  or  area,  of 
the  present  mines,  of  as  much  as  1000  or  2000  feet.  This  fact 
is  mentioned  to  show,  that,  even  if  the  objection  generally  pre- 
sented to  the  possibility  of  the  descent  of  oxide-bearing  waters 
below  the  groundwater-level  be  admitted  to  be  valid,  it  would 
not  necessarily  prove  that  the  sulphides,  at  present  below  that 
level,  could  not  have  been  enriched  by  descending  waters,  since 
before  the  faulting  they  may  have  been  above  it. 

Since  my  first  examination  of  Butte,  I  have  had  opportunities 
of  seeing  most  of  the  important  copper-deposits  of  the  West, 
and  my  associate,  Mr.  "Weed,  has  visited  many  in  the  Appa- 
lachian region ;  I  have  also  examined  the  literature  of  the  sub- 
ject for  facts  bearing  upon  the  question  under  consideration. 
Although  no  case  has  come  under  my  notice  in  which  the  de- 
velopment of  secondary  sulphides  has  been  comparable,  either  in 
extent  or  in  amount,  with  that  of  Butte,  a  brief  mention  of  the 
prominent  facts  is  made  as  confirmatory  evidence. 

Western  Copper-Deposits. — In  the  first  place,  it  should  be 
stated  that  the  occurrence  of  a  belt  of  rich  sulphides  immedi- 
ately below  the  water-level  is  by  no  means  universal.  It  is  not 
found,  as  far  as  I  know,  in  the  massive  pyrrhotite-deposits  of 
Canada,  in  which  one  passes  directly  from  a  relatively  thin 
gossan  into  unaltered  copper-bearing  pyritous  ore.  The  most 
obvious  explanation  of  their  absence  there  would  at  first  appear 
to  be  the  cold  climate  and  the  comparatively  recent  planing  off 
of  the  surface  by  the  continental  ice-sheet.  I  should  be  in- 
clined to  consider  the  dense  charcter  of  the  material  of  the  de- 
posits, and  the  possible  absence  of  recent  fractures,  which  would 
have  admitted  an  easy  access  of  surface  waters,  as  equal,  or 
possibly  more  important  factors. 

In  the  arid  climate  of  Arizona  and  New  Mexico,  on  the 
other  hand,  and  still  more  in  Old  Mexico,  it  is  often  difficult  to 
find  the  zone  of  unaltered  sulphides,  so  deep  has  the  oxidizing 
action  penetrated.  A  recent  note  on  the  mines  near  Mapimi 
in  the  State  of  Durango  states  that  this  zone  had  not  been 
reached  at  a  depth  of  2500  feet.* 

*  H.  Van  F.  Furman,  Proc.  Colo.  Sci.  Soc.,  Jan.,  1900. 


446  THE    SECONDARY    ENRICHMENT    OF    ORE-DEPOSITS. 

"Wendt,  in  his  review  of  the  copper-deposits  of  Arizona  and 
New  Mexico,*  makes  some  very  suggestive  remarks  as  to  the 
chemistry  of  the  deposits,  though  he  does  not  always  seem  to 
appreciate  to  their  full  extent  their  geological  bearing.  He 
notes,  as  a  general  fact,  that  the  ores  in  limestone  are  mainly 
carbonates  and  oxides,  while,  in  the  comparatively  acid  erupt- 
ive-rocks at  corresponding  levels,  they  are  more  likely  to  be 
sulphides.  In  several  cases  he  suggests  the  probability  of  sec- 
ondary migrations.  For  instance,  with  regard  to  the  limestone- 
deposits  of  the  Bisbee  district,  he  says  :f 

"  Contrary  to  the  generally  accepted  theory  of  the  occurrence  of  oxidized  cop- 
per-ores, the  writer  has  doubts  whether  the  ores  of  this  district,  as  far  as  known, 
have  ever  been  sulphurets  in  their  present  position.  The  whole  deposition  tends 
to  prove  that  the  ores  are  not  a  secondary  decomposition  or  alteration  of  what  was 
formerly  sulphurets,  but  have  been  precipitated  as  carbonates  from  an  acid-solu- 
tion which  carried  them  from  the  depths  below." 

In  speaking  of  vertical  lead-bearing  veins  in  the  limestone  at 
a  higher  horizon  than  the  copper-deposits,  he  says :  J 

"In  depth  the  lead -carbonates  have  invariably  given  out,  and  what  ore  is  found 
in  depth  in  these  vertical  fissures  is  copper-ore.  It  is  probable  that  these  veins  are 
spurs  of  the  great  bed-veins  opened  in  the  Queen,  Prince  and  other  mines." 

Of  the  veins  in  porphyry  in  the  same  district,  he  says :  § 

"  The  oxidized  copper-ore,  as  usual  in  siliceous  rocks,  changed  into  copper- 
glance  but  little  below  the  outcrop.  At  an  inconsiderable  depth  it  became  very 
much  impoverished  and  pinched.  In  fact,  here  as  elsewhere,  the  copper-glance 
appears  to  be  not  a  true  ore  at  all,  but  a  product  of  decomposition  and  of  secondary 
origin  derived  from  the  leaching  of  the  vein  above  and  subsequent  concentration 
at  a  lower  point.  To  those  conversant  with  the  beautiful  process  of  kernel  roast- 
ing, the  presence  of  a  zone  of  copper-glance  presents  a  similar  phenomenon  on  the 
grand  scale  of  nature's  work.  The  oxidation  of  pyritous  croppings  is  but  a  roast- 
ing carried  out  during  ages  by  the  combined  action  of  air  and  moisture." 

In  his  recent  paper  on  the  Copper  Queen  mine,||  Dr.  James 
Douglas  gives  it  as  his  opinion  that  the  deposits  in  limestone 
were  "  originally  more  or  less  compact  iron  pyrites  carrying  a 
small  percentage  of  copper;"  and  that  during  the  progress  of 
alteration  "  the  copper  by  a  process  of  segregation,  akin  to 
crystallization,  was  concentrated  and  collected  into  areas  of 
limited  size,  thus  constituting  the  comparatively  small  bodies 

*  Trans.,  xv.,  25.  f  Op.  tit.,  55. .  J  Op.  dt.,  59. 

\  Op.  tit.,  57.  ||   Trans.,  xxix.,  pp.  511,  531,  534. 


THE    SECONDARY    ENRICHMENT    OF    ORE-DEPOSITS.  447 

of  oxidized  ores  which  are  disseminated  irregularly  through 
the  very  large  masses  of  ledge-matter."  More  pertinent  to 
the  question  under  discussion,  however,  is  his  description  of 
the  great  mass  of  compact  pyrites  extending  from  the  200  to 
the  400-foot  level  on  which  "  a  string  of  stopes,  nearly  500 
feet  in  length,  has  been  opened,"  which  is  decomposed  on 
the  exterior  and  surrounded  by  a  zone  of  altered  limestone  and 
of  aluminous  matter,  generally  barren  of  copper.  "  Roughly 
speaking,"  he  says,  "  the  mass  is  enveloped  in  a  shell  of 
oxysulphide,  and  streaks  of  similar  black  copper-ore  of  good 
grade  intersect  it ;  but  the  core  consists  of  compact  bisulphide 
of  iron  very  lean  in  copper."  Oxidized  ores  extend  to  a  con- 
siderable depth  below  this  mass,  for  which  he  offers  the  same 
explanation  that  I  do :  namely,  that  the  pyrite  mass  was  more 
dense  and  impermeable  than  the  rock  mass  below,  and  that 
the  oxidizing  waters  penetrated  it  but  slowly. 

I  have  given  priority  to  the  observations  of  these  gentlemen 
where  they  confirm  my  own,  because  they  are  the  result  of 
much  more  extended  studies  than  it  was  possible  for  me  to 
make  in  the  limited  time  at  my  command. 

Of  the  four  great  copper-producing  districts  of  Arizona, 
three,  namely,  Bisbee,  Globe  and  Clifton-Morenci,  resemble 
each  other,  in  that  the  deposits  occur  in  a  region  of  limestones 
and  intrusive  eruptive-rocks  and  under  climatic  conditions  of 
extreme  aridity.  The  fourth,  the  United  Yerde  mine,  near 
Prescott,  which  has  a  somewhat  greater  precipitation,  owing 
to  its  vicinity  to  the  Plateau  region  of  northeast  Arizona,  is  in 
a  vertical-shear  zone  of  old  (probably  Algonkian)  slates  and 
intruded  dioritic  rocks,  the  neighboring  limestones  being  of 
later  age,  unconformably  superposed,  and  apparently  having 
no  connection  with  the  deposits.  The  physical  conditions  there 
more  nearly  resemble  those  of  Butte  than  at  either  of  the  other 
localities,  and  an  underground  study  would  probably  have 
been  most  instructive.  Unfortunately,  the  policy  of  the  exclu- 
sion of  visitors  pursued  by  the  owner  was  strictly  enforced  in 
my  case,  and  I  could  only  determine  that  rich  sulphides  do 
occur  beneath  the  gossan. 

At  Bisbee  the  Copper  Queen  deposits,  which  include  all  that 
were  actively  worked  at  the  time  of  my  visit,  are  in  flat-lying 
limestones  which  are  underlaid  by  quartzites  and  have  not 


448  THE    SECONDARY    ENRICHMENT    OF    ORE-DEPOSITS. 

been  developed  to  any  great  vertical  depth,  so  that  I  can  only 
confirm  the  evidence  already  presented  that  there  have  evi- 
dently been  considerable  migrations  in  the  ore  since  they  were 
originally  deposited,  and  that  their  original  form  was  probably 
low-grade  pyritous  masses  of  great  size,  the  ores  at  present 
worked,  both  oxides  and  sulphides,  being  concentrations  pro- 
duced by  these  migrations. 

At  Globe,  the  principal  copper-deposits  lie  along  a  great  east 
and  west  fault-plane,  through  the  displacement  of  which  lime- 
stones have  been  brought  down  in  juxtaposition  to  underlying 
quartzites  and  intruded  sheets  of  dioritic  rock.  Some  isolated 
bodies  of  ore  are  said  to  occur  in  the  dioritic  rocks,  and, 
according  to  Wendt,  these  are  mostly  sulphides.  Those  which 
I  saw,  and  which  constitute  the  main  mass  of  the  copper-ore, 
are  in  the  limestones  on  the  south  of  the  fault.  The  ores  thus 
far  opened  have  been  mainly  carbonates  and  oxides,  but  in 
the  lower  levels,  400  to  500  feet  below  the  surface,  the  latter 
are  passing  into  the  dull  earthy-looking  glance,  called  "  black 
sulphide,"  which  is  the  characteristic  alteration  product  at  the 
line  between  oxides  and  sulphides.  The  original  ore-deposi- 
tion appears  to  have  occurred  mainly  along  the  great  fault- 
fissure,  and  secondary  migrations  to  have  taken  place  along 
subordinate  fractures  either  nearly  parallel  or  at  right  angles 
to  it,  which  evidently  formed  channels  for  the  surface-waters. 
It  was  noticeable  that  here,  as  Dr.  Douglas  has  stated  to  be 
the  case  at  Bisbee,  cuprite  and  native  copper  are  more  com- 
mon in  the  lower  part  of  the  oxidized  zone,  and  the  carbonates 
nearer  the  surface. 

In  the  Clifton-Morenci  district,  near  the  borders  of  New 
Mexico,  the  area  of  mineralization  is  much  larger  and  the  geo- 
logical conditions  are  more  complicated.  A  series  of  quartzites 
and  limestones  resting  on  granite  have  been  extensively  cut 
through  by  igneous  intrusions  of  both  basic- and  acid-eruptives, 
and  since  broken  by  a  complicated  system  of  faults.  The  orig- 
inal mineralization  apparently  took  place  along  shear-zones  or 
faults ;  the  ore  is  found  both  in  the  eruptive-rocks  and  in  a  cer- 
tain horizon  of  limestone. 

The  mines  were  long  worked  for  the  rich  carbonate  ores  near 
the  surface  which  are  now  in  great  measure  exhausted, 
at  present  the  most  common  ore  is  the '  so-called  "  black 


THE   SECONDARY   ENRICHMENT    OF   ORE-DEPOSITS.  449 

uret,"  the  dull-black  glance  above  mentioned.  This,  I  found, 
as  in  Globe,  immediately  below  the  ores  of  cuprite  and  native- 
copper.  In  the  larger  veins,  spots  of  pyrite  can  be  detected  within 
the  glance  which  constitutes  the  rich  ore.  In  the  porphyry 
adjoining  is  a  net-work  of  narrow  veins  or  joints  filled  with 
glance.  This  constitutes  the  lower  grade,  or  concentrating-ore 
which  is  remarkably  free  from  other  metals  than  copper,  and 
appears  to  have  been  formed  by  migration  from  a  main  body. 
Below  the  ore-bearing  zone,  the  limestones  are  impregnated 
with  practically  barren  pyrites,  and  the  porphyry  below  the 
ore-bearing  zone  has  its  joints  also  filled  with  pyrites.  In  some 
cases  the  direct  passage  of  the  glance  into  the  low-grade  pyrites 
could  be  observed. 

The  Coronado  mines,  famous  in  the  early  days,  but  now 
abandoned,  exhibited  a  vertical  ore-body  within  a  dike  of 
quartz-porphyry  which  cuts  through  the  basal  granite.  Of  this 
ore-body  Wendt  says  :  * 

1 1  Whenever  the  copper-glance  in  the  Coronado  mines  has  been  followed  down, 
it  disappears  at  a  depth  of  150  or  200  feet  from  the  surface,  and  either  the  vein 
becomes  barren,  or  the  glance  is  replaced  by  yellow  sulphurets  sparingly  dis- 
seminated through  the  gangue." 

In  New  Mexico,  the  Santa  Rita  mine  is  famous  as  having  been 
worked  at  a  profit  early  in  the  past  century  under  Mexican  rule. 
It  lies  about  15  miles  east  of  Silver  City,  ^T.  M. ;  the  ore  is 
found  in  a  white  quartz-porphyry  which  was  evidently  once 
covered  by  horizontally  bedded  limestones  that  still  lie  round 
the  rim  of  the  shallow  basin  where  it  occurs.  The  richest  ores 
have  been  removed  from  the  surface,  and,  as  the  underground 
workings  were  inaccessible,  my  hastily-formed  opinion  of  the 
deposits  would  not  be  of  much  value,  except  that  I  came  to  it 
fresh  from  an  examination  of  others  in  which  many  analogous 
conditions  occur.  As  at  present  seen,  the  porphyry  at  the  sur- 
face is  impregnated  with  a  thin  coating  of  azurite  on  joint-faces 
and  in  spots  through  the  mass  of  the  rock.  At  some  depth 
below  the  surface  cuprite  and  native-copper  are  associated  to- 
gether, largely  as  the  filling  of  narrow  joint-seams,  and  pass 
still  lower  down  into  the  dull  copper-glance  similarly  distrib- 
uted. From  the  evidence  of  the  dumps,  pyrite  occurs  at  still 
greater  depths,  but  in  quite  limited  quantity. 

*  Trans.,  xv.,  38. 


450  THE   SECONDARY   ENRICHMENT    OF    ORE-DEPOSITS. 

My  judgment  was,  that  most  of  this  ore  had  been  formed  by 
leaching  down  from  the  low-grade  pyritous  body  in  the  lime- 
stones which  once  covered  the  porphyry.  Considerable  bodies 
of  hematite-ore,  evidently  the  result  of  oxidation-in-place  of 
bodies  of  pyrite,  are  frequent  in  the  limestones  of  this  region; 
and,  in  the  Hanover  mine,  it  is  said  that  copper-ores  have  been 
found  in  the  pyrite  immediately  under  the  hematite. 

In  Bingham  Canon,  Utah,  where  the  climatic  conditions  are 
intermediate  between  those  of  Butte  and  of  Arizona,  old  mines, 
which  were  once  worked  for  the  value  of  their  pyritous  ores  in 
lead  and  silver,  are  now  being  reopened,  because  the  same  py- 
rite-bodies  are  found  in  depth  to  contain  enough  copper  to  pay 
for  working  under  present  economic  conditions.  The  ores  oc- 
cur as  a  replacement  of  certain  limestone-beds  in  a  great  series 
of  quartzites  that  are  cut  by  intrusive  bodies  of  porphyry  and 
have  subsequently  been  faulted. 

In  the  Highland  Boy  mine,  which  I  visited  last  summer,  I 
found  a  large  body  of  pyrite  replacing  limestone  in  the  imme- 
diate vicinity  of  a  body  of  quartz-porphyry.  Portions  of  this 
body,  which  were  compact  and  unaltered,  were  too  lean  to  work. 
Along  certain  lines  of  post-mineral  fracturing  or  faulting,  how- 
ever, the  mass  was  found  to  be  altered  and  constituted  an  ore 
that  was  said  to  average  8  per  cent,  in  copper.  In  those  places 
where  the  enrichment  was  visible  to  the  eye,  a  little  copper- 
glance,  with  the  dull  earthy  appearance  that  is  character- 
istic of  the  recently  formed  secondary  mineral,  could  be  dis- 
tinguished. 

Western  Silver  Deposits. — Instances  of  probable  secondary  en- 
richment of  silver-bearing  deposits  from  my  earlier  examina- 
tions, now 'occur  to  me  as  I  look  back,  but  as  they  were  not  ex- 
amined critically  with  a  view  to  this  explanation  of  their  form- 
ation, I  place  less  weight  upon  them. 

Most  famous,  in  view  of  the  enormous  values  taken  from 
th^m,  are  the  rich  silver-bodies  of  the  Mollie  Gibson  and 
Smuggler  mines  of  Aspen,  Colo. ;  but,  in  their  case,  there  is 
sufficient  organic  matter  present  to  explain  the  reduction  of  the 
oxidized  solutions  to  sulphides.*  They  occur  along  a  vertical 
fault  formed  since  the  original  mineralization  of  the  district, 


U.  S.  Geol.  Sur.,  Mon.  xxxi.,  Aspen"  Mg.  Dist.,  p.  183. 


THE    SECONDARY   ENRICHMENT    OF    ORE-DEPOSITS.  451 

and  consist  of  great  masses  of  polybasite  and  pink  barite,  which, 
in  places,  have  been  further  reduced  to  native-silver.  On  one 
wall  of  the  ore-body  is  the  limestone,  of  which  it  is  a  replace- 
ment, and  on  the  other,  a  black  bituminous  shale. 

In  the  San  Juan  region  of  Colorado,  there  is  a  very  strong 
belief  held  by  some  of  the  more  experienced  and  thoughtful 
mining  engineers,  that  the  rich  silver-minerals  in  their  veins, 
such  as  ruby-  and  brittle-silver,  are  the  result  of  secondary  en- 
richment by  descending  waters.  The  most  notable  instance 
presented  (which,  however,  I  have  not  yet  had  opportunity  of 
verifying  by  personal  observation)  is  that  of  the  famous  Smug- 
gler-Union vein,  which  has  been  opened  for  some  four  miles  on 
the  strike,  and  in  places  to  a  depth  of  nearly  1,000  feet.  The 
main  vein  has  a  width  of  several  feet  of  comparatively  low- 
grade  concentrating-ore,  while  on  the  foot-wall  is  a  streak  a 
few  inches  thick  of  rich  "  shipping  "  ore,  which  carries  the  rich 
silver-minerals.  The  main  vein  has  been  displaced  about  50 
feet  by  the  Pandora  vein,  which  crosses  it  at  right  angles  and 
carries  gold-values,  though  not  in  paying  quantity.*  Accord- 
ing to  my  informants,  the  foot-wall  streak  is  not  sensibly 
affected  by  the  faulting ;  and  they  reason  that  it  is  a  plane  of 
recent  movement,  on  which  the  silver-minerals  have  been  con- 
centrated by  a  secondary  migration  from  the  main  vein. 

In  several  important  veins  in  the  San  Juan  region,  I  ob- 
served secondary  or  post-mineral  fractures  parallel,  and  more 
or  less  coincident,  with  the  plane  of  the  vein,  but  no  detailed 
studies  have  yet  been  made  that  would  determine  whether 
there  has  been  an  enrichment  of  the  minerals,  or  not. 

In  unpublished  notes  on  the  once  famous,  but  now  aband- 
oned, Yankee  Girl  mine,  in  the  Red  Mountain  district  of  the 
same  region,  I  find  mention  of  a  phenomenon  which  then  ap- 
peared unexplainable,  but  which  it  now  appears  might  be 
accounted  for  on  the  theory  of  secondary  enrichment.  In  the 
upper  levels,  the  ores,  down  to  about  200  feet  from  the  surface, 
were  mainly  silver  and  lead,  galena  and  pyrite  being  the  prin- 
cipal minerals.  Below  this  zone,  the  ore  is  mainly  composed 
of  stromeyerite,  bornite,  chalcocite,  with  some  gray-copper  and 
barite,  yielding  about  30  per  cent,  of  copper,  and  little  or  no 

*   U.  S.  Geol.  Sur.,  18th  Ann.  Rep.,  Pt.  iii.,  p.  834. 
29 


452  THE    SECONDARY   ENRICHMENT    OF    ORE-DEPOSITS. 

lead.  In  depths  below  600  or  TOO  feet,  the  ore  in  this  and 
adjoining  mines  is  said  to  have  gradually  turned  into  a  low 
grade  pyritous  ore,  which  was  of  too  low  grade  to  work  at  a 
profit,  and  caused  the  mines  to  be  closed  down.  The  ores  in 
the  copper-bearing  zone  had  been  exceptionally  rich,  carrying 
several  thousand  ounces  of  silver  to  the  ton  in  carload  lots. 
The  waters  in  this  region,  both  mine-waters  and  spring-waters, 
are  unusually  acid,  the  latter  forming  abundant  deposits  of 
limonite,  while  the  former  rapidly  corrode  any  metallic  iron- 
materials,  such  as  water  pipes,  that  are  exposed  to  their  action. 

The  most  definite  instances  of  secondary  enrichment  of  silver 
sulphides  are,  however,  those  described  by  Weed,  in  the  mines 
of  Neihart,  Mont.*  There  the  veins  have  suffered  later  fractur- 
ing and  secondary  enrichment  of  the  zone  at  or  below  the  w^ater- 
level,  with  the  deposition  of  silver  sulphides  "  as  crusts  or  crys- 
tals lining  cavities,  or  as  films  or  thin  coatings  along  fractures 
of  the  primary  ore."  The  primary  minerals  are  galena,  blende 
and  pyrite ;  the  secondary  sulphides  are  polybasite,  ruby-silver, 
more  rarely  a  pure  transparent  blende.  Under  the  microscope 
galena  is  seen  altering  to  a  spongy  polybasite.  Polybasite  and 
pyrargyrite  are  seen  as  crystalline  aggregates  and  crusts  on  all 
other  minerals,  but  in  no  case  coated  by  other  minerals.  The 
immediate  products  of  superficial  alteration,  the  gossan,  are 
largely  removed  and  make  up  a  zone  at  most  only  a  few  feet 
thick.  Beneath  this  is  an  irregular  accumulation  of  sooty 
black  ore,  consisting  of  manganese  and  silver  sulphide.  "Where 
the  vein  is  well-defined  the  secondary  antimonial  sulphides 
occur  below,  at  first,  in  considerable  abundance,  but  deeper 
down,  only  in  crevices  or  fissures  partly  or  wholly  lining  filled 
fractures,  so  that  they  become  less  and  less  abundant  in  going 
down  on  the  vein. 

Eastern  Examples. — In  his  description  of  the  lead-  and  zinc- 
deposits  of  the  Mississippi, f  W.  P.  Jenney  notes  interesting  in- 
stances of  deposition  by  descending-solutions  below  the  zone 
of  oxidation. 

Among  minerals  of  secondary  deposition  he  enumerates 
"  blende,  galena,  chalcopyrite  and  greenockite,  produced  by 

*  U.  S.  Geol.  Sur.,  21s£  Ann.  Rep.,  Pt.  iii.     "The  Geology  of  the  Little  Belt 
Mountains,"  by  W.  H.  Weed,  p.  421. 
f  Trans.,  xxii.,  199. 


THE    SECONDARY    ENRICHMENT    OF    ORE-DEPOSITS.  453 

alteration  from  the  primary  ores  in  the  zone  of  oxidation  in 
the  upper  part  of  the  ore-bodies,  and  re-formed  as  sulphides  by 
the  reducing  action  of  organic-matter  in  the  deeper  levels." 

lies*  and  Kobertsonf  have  also  described  secondary  deposits 
of  zinc-sulphide  which  are  assumed  by  them  to  have  been  de- 
posited from  a  sulphate  solution  through  the  agency  of  sul- 
phuretted hydrogen. 

In  the  Southern  Appalachian  region  are  many  copper-de- 
posits which  show  excellent  instances  of  secondary  enrichment 
through  the  agency  of  mineralizing  waters.  Most  of  these  have 
recently  been  examined  by  Mr.  Weed,;f  and,  as  detailed  descrip- 
tions of  them  will  be  found  in  his  paper  on  "  Types  of  Copper- 
Deposits  in  the  Southern  United  States,"  presented  at  this  meet- 
ing, only  a  brief  mention  of  the  salient  points  need  be  made 
here. 

Best  known  are  the  deposits  of  Ducktown  in  the  extreme 
southeast  corner  of  Tennessee,  which  have  become  classic  in 
the  literature  of  ore-deposits  for  their  black  copper-ores  which 
form  a  narrow  band  between  the  gossan  and  the  unaltered  py- 
ritous  ore  beneath.  The  gossan-ores  are  immense  masses  of 
porous  iron-oxide  which  are  so  free  from  impurities  as  to  be 
used  in  large  quantities  in  the  blast-furnaces  of  Tennessee  and 
Virginia.  The  original  ore  is  an  irregular  mixture  of  pyrrho- 
tite  and  chalcopyrite,  quite  massive  and  free  from  vertical  frac- 
turing. The  comparatively  thin  zone  of  black  ore  has  been 
considered  to  be  a  mixture  of  black  oxide  and  sulphuret  of  cop- 
per ;  but  chemical  examination  of  the  specimens  brought  in  by 
Mr.  Weed  and  those  in  the  National  Museum  show  only  cop- 
per-glance and  no  tenorite.  The  ore  is  impregnated  with  cop- 
per sulphate,  showing  that  the  process  of  concentration  is  still 
going  on,  and  recently-formed  amorphous  black  sulphuret  is 
found  in  clefts  in  the  upper  surface  of  the  pyrrhotite. 

When  the  black  ores  were  first  developed  many  curious 
speculations  were  current  as  to  their  origin;  but  Whitney§ 
early  recognized  their  true  source,  as  is  most  evident  in  his  re- 
ply to  Tuomey  in  1855,  where  he  ascribes  these  rich  sulphides 

*  Eng.  and  Min.  Jour.,  vol.  xlix.,  1890,  p.  499. 
t  Am.  Jour.  Sci.,  3d  series,  vol.  xl.,  p.  160. 
J  Bull.  Geol.  Soc.  Amer.,  vol.  xi.,  pp.  179-206. 
I  Metallic  Wealth  of  the  United  States,  p.  322. 


454  THE    SECONDARY    ENRICHMENT    OP    ORE-DEPOSITS. 

to  an  enrichment  of  the  original  ore  through  the  decomposi- 
tion of  the  zone  above  (now  gossan).* 

Sterry  Huntf  makes  allusion  to  this,  and  similar  deposits,  at 
Ore  Knob,  IsT.  C.,  and  in  Carroll  county,  Ya.,  as  owing  "  their 
origin  to  the  reduction,  in  some  imperfectly  explained  way,  of 
the  sulphates  formerly  generated  by  oxidation  in  the  upper 
portion  of  the  lodes,"  and  OlcottJ  confirms  his  view  as  to  the  Ore 
Knob  deposit.  In  all  these  cases,  however,  the  enrichment  is 
assumed  to  have  taken  place  at  or  above  the  water-level,  and 
there  is  no  question  of  its  extending  to  any  considerable  dis- 
tance below  it. 

In  the  Union  Copper  Company's  mine  at  Gold  Hill,  IN".  C., 
as  reported  by  Mr.  "Weed,  the  ore-body  is  fractured  by  vertical 
planes  which  penetrate  to  some  depths  below  the  oxide  zone. 
There  are  here  no  such  great  masses  of  pyritous  ore  as  at  Duck- 
town,  the  primary  ore  being  vein-quartz  carrying  a  small 
amount  of  chalcopyrite.  Owing  to  the  vertical  fractures  the 
lower  limits  of  the  brown  oxidized  ore  are  very  irregular,  ex- 
tending in  places  down  to  180  feet  or  more  below  the  surface 
and  half  that  distance  into  solid  unaltered  quartz-ore.  The 
surface-ores  were  originally  worked  for  gold,  but  the  increase 
of  copper  with  depth  interfered  with  amalgamation. 

The  workings  now  extend  to  a  depth  of  over  250  feet.  In  the 
main  part  of  the  vein  are  rich  masses  of  chalcopyrite  in  quartz 
which,  when  altered,  change  directly  into  chalcocite ;  the  latter 
is  often  surrounded  by  a  film  of  cuprite,  which,  in  turn,  changes 
to  fibrous  malachite  along  cracks  in  the  quartz.  Where  the 
alteration  has  proceeded  further,  specimens  are  found  showing 
copper-glance  coated  with  crystalline  cuprite  and  native  silver; 
others  show  crystalline  glance  passing  directly  into  native  cop- 
per, which  forms  a  thin  felty  covering  up  to  a  quarter  of  an 
inch  thick.  Nearer  the  oxide  zone,  a  sooty  black  mass  is  often 
found  directly  replacing  the  chalcopyrite. 

Specimens  from  the  Blue  Wing  mine  in  the  Yirgilina  district 
on  the  borders  of  Virginia  and  North  Carolina,  taken  from  be- 
low the  oxide  zone,  show  bornite  surrounded  by  a  shell  of  dull 
glance  with  iron  oxide  outside.  Other  specimens  from  below 


*  Amer.  Jour  /Set.,  2d  series,  vol.  xx.,  p.  53. 

f  Trans.,  ii.,  127.  J  Trans.,  iii.,  392. 


THE    SECONDARY    ENRICHMENT    OF    ORE-DEPOSITS.  455 

the  water-level  show  bornite  altered  to  chalcoeite,  while  the 
iron  is  concentrated  in  the  form  of  nests  of  specular  iron  in  the 
quartz.  These  ores  extend  to  the  present  limits  of  the  work- 
ings 300  feet  below  the  surface.  That  they  will  pass,  like  those 
of  Gold  Hill,  into  chalcopyrite  in  depth,  cannot  yet  be  pre- 
dicated with  certainty. 

Foreign  Authorities. — Although  it  was  the  Austrian  geologist, 
Posepny,  already  cited,  who  most  strongly  emphasized  the  dis- 
tinction between  the  results  of  the  action  of  surface-  and  deep- 
seated  waters,  European  geologists  seem  to  have  been,  as  a 
rule,  slower  to  recognize  this  distinction  in  their  practice  than 
American  mining  geologists,  whose  views  are  generally  gath- 
ered from  a  wider  field  of  observation. 

The  brilliant  French  writer,  DeLaunay,*  has  been  cited  by 
Mr.  Weed  as  one  who  seems  to  have  conceived  the  idea  that 
the  enrichment  of  sulphides  by  descending  surface-waters  has 
been  an  important  element  in  the  formation  of  ore-deposits ;  and 
indeed  the  title  of  his  most  recent  theoretical  discussion  of  the 
question  gives  ground  for  this  supposition. 

A  careful  reading  of  this  and  his  other  papers,  however,  leads 
rather  to  the  conclusion  that  the  secondary  migrations  he  con- 
templated were  confined  to  the  zone  above  the  groundwater-level, 
or  oxidized  zone,  in  which  sulphides  have  always  been  known 
to  occur.  The  novelty  of  his  view  would  appear  to  be  that 
they  are  not  necessarily  residual  masses  of  sulphides  that  have 
not  been  completely  oxidized,  but  that  in  many  cases  they  re- 
sult from  an  actual  transference  of  material  and  a  re-deposition 
as  sulphides.  Thus,  in  closing  his  discussion  on  the  origin  of 
copper  and  ore-deposits, f  he  says  : 

"What  is  the  origin  of  the  modifications  which  have  been  noted  in  a  general 
way  in  the  upper  part  of  a  vein  ;  modifications  undoubtedly  connected  with  near- 
ness to  the  surface,  and  which  disappear  in  depth  ?  Is  it  possible  that  these  modi- 
fications have  sometimes  been  produced  contemporaneously  with  the  filling  of  the 
vein,  or  are  they  always,  as  is  incontestably  the  case  in  many  instances,  the  result 

*  "I.  On  the  importance  of  deposits  by  magmatic  inclusion  and  segregation  in 
a  classification  of  ore-deposits. 

"II.  On  the  part  played  by  the  phenomena  of  superficial  alteration  and  the 
renewal  of  movement  (migrations)  in  the  formation  of  ore-deposits." — Ann.  des 
Mines,  9th  series,  xii.,  1897,  p.  119-228. 

f  Gites  Mine'raux  et  Me*tallif£res,  Paris,  1893,  vol.  ii.,  p.  232. 


456  THE    SECONDARY   ENRICHMENT    OF    ORE-DEPOSITS. 

of  much 'later  action  ;  especially  of  the  introduction  of  surface-waters  down  to  a 
certain  level  called  hydrostatic?" 

In  his  later  paper,  after  describing  the  succession  of  minerals 
found  in  the  silver-deposits  of  Mexico  and  South  America  as 
an  upper  zone  of  chlorides  and  native  metals,  and  helow  this  a 
bonanza-zone,  where  the  silver  and  copper  "  coming  in  part 
from  the  surface  "  are  concentrated  by  a  sort  of  cementation  as 
rich  sulphides,  etc.  (both,  however,  being  above  the  water-level), 
he  speaks  of  the  chemical  processes  that  have  probably  gone 
on,  as  follows : 

"  The  atmospheric-waters  reached  the  deposit  by  descending  and  filtering  down 
slowly  along  the  plane  of  the  vein  to  ascend  again  to  the  surface  only  after  a  cir- 
cuit that  is  more  or  less  long  and  complex.  It  results  that  the  elements  dissolved 
are  not  absolutely  lost  to  the  vein,  but,  on  the  contrary,  a  great  part  of  them  are 
only  slightly  displaced  from  above  downward,  and  are  re-precipitated  in  depth  in 
contact  with  unaltered  sulphides  in  the  form  of  insoluble  sulphides.  This  sec- 
ondary phenomenon,  which  is  particularly  marked  for  copper  and  silver,  often 
brings  about  a  special  concentration  of  these  two  metals  at  a  certain  distance  below 
the  surface,  so  that  below  the  oxides  and  carbonates  that  characterize  the  actual 
outcrop  is  found  a  very  rich  zone,  or,  as  the  miners  of  the  New  World  express  it, 
a  bonanza,  in  which  copper  forms  gray-copper,  glance,  bornite,  etc.  ;  while  silver 
separates  as  argentite,  brittle-silver  and  ruby  silver." 

European  Deposits. — The  great  pyrite-deposits  of  Rio  Tinto, 
Tharsis,  etc.,  in  the  Huelva  provinces  of  southern  Spain,  are 
enormous  bodies,  analogous  in  geological  conditions  to  those 
of  Ducktown,  but  of  even  greater  volume.  The  gossan,  which 
extends  down  to  a  depth  of  130  to  150  feet,  consists  mainly 
of  iron  oxide,  with  50  to  55  per  cent,  iron,  a  little  sulphur  and 
arsenic,  and  only  a  trace  of  copper.  Between  this  and  the 
solid  pyrite  below  is  a  very  regularly  distributed  zone  of  earthy, 
porous  material,  from  a  few  inches  to  a  foot  in  thickness,  carry- 
ing an  average  value  of  about  $35.00  per  ton  in  gold  and 
silver.  These  values  it  is  assumed  by  Yogt,*  who  has  last 
written  upon  the  region,  have  been  brought  down  in  solution 
by  ferric  sulphate  which,  in  contact  with  the  underlying  pyrite, 
has  been  reduced  to  ferrous  sulphate,  with  precipitation  of  the 
gold  and  silver.  It  is  in  the  pyrite-mass  below  the  "  iron  hat " 
that  the  copper-values  are  found ;  and  these  gradually  decrease 
with  depth  from  4  to  5  per  cent,  in  the  upper  100  to  200  feet 

*  Zeitschr.  Prak.  Geol,  July,  1899,  pp.  249,  250. 


THE    SECONDARY    ENRICHMENT    OF    ORE-DEPOSITS.  457 

to  1 J  per  cent,  at  the  depth  of  900  feet — varying  somewhat  with 
local  conditions.  The  geologists  who  have  studied  the  region 
account  for  this  decrease  by  assuming  that,  during  the  oxidation 
of  the  gossan,  the  original  copper-contents  were  leached  down 
and  re-precipitated  in  recent  fractures  and  clefts  in  the  pyrite 
mass,  thus  enriching  its  upper  part.  Says  Vogt : 

"  In  point  of  fact  we  find  such  minerals — copper-glance,  bornite  and  chalco- 
pyrite, sometimes  with  galena,  zinc-blende  and  gray-copper,  and,  as  a  rule,  ac- 
companied by  quartz — very  often  in  clefts  and  cracks  in  pyrite,  and  these  min- 
erals are,  without  doubt,  of  younger  (secondary)  formation.  At  times  these  clefts 
are  so  large  that  they  can  be  separately  mined  ;  thus,  the  old  Roman  mining  was 
done  chiefly  on  these  richer  clefts  within  the  poorer  mass  of  pyrite.  Most  com- 
monly, however,  they  are  quite  small  and  constitute  a  strongly  branching  net- 
work in  the  normal  pyrite-mass  ;  and  that  the  copper-content  of  these  secondary 
minerals  is  derived  from  the  weathered,  superficial  mass  is  shown  quite  simply  in 
the  fact  that  these  veins  are  most  common  in  the  zone  immediately  under  the 
'iron  hat.'  They  extend  downward  something  like  a  hundred  meters  or  more, 
and  then  commences  the  solid  pyrite-mass,  little  fissured  and  comparatively  bar- 
ren of  copper." 

He  also  mentions  a  decrease  of  copper-contents  with  depth 
in  the  great  vertical  pyrite-deposits  of  Vigsnas,  in  Norway, 
and  Fahlun,  in  Sweden,  of  which  the  former  has  been  worked 
to  a  depth  of  735  meters  and  the  latter  to  350  meters. 

At  Monte  Catirii,  in  Italy,  the  rich  copper-ore  occurs  in 
masses  sometimes  of  several  cubic  metres  in  size  with  an 
arrangement  of  concentric  zones  which  grow  successively 
richer  in  copper  towards  the  periphery.  These  masses  are 
sometimes  isolated;  sometimes  connected  with  metalliferous 
veins.  Balls  of  glance  occur  sometimes  the  size  of  a  man's 
head.  The  larger  masses  consist  of  chalcopyrite  at  the  center, 
surrounded  first,  by  bornite,  and  then  on  the  outside  by  chalco- 
cite,  which  sometimes  passes  into  native-copper.  These  rich 
masses  occur  in  a  zone  of  recent  movement  which  is  easily 
penetrable  by  surface-wTaters.  In  depth  the  rich  sulphides  cease 
and  the  ore  consists  of  chalcopyrite  and  pyrite,  the  latter  be- 
coming more  and  more  predominant  with  depth. 

There  are  many  other  European  examples  which  would 
doubtless  show  evidence  of  secondary  enrichment,  if  examined 
with  that  question  in  view.  In  the  great  zinc-,  lead-  and  silver- 
deposits  of  Laurium,  in  Greece,  for  instance,  it  seems  that  this 
process  might  explain  some  of  the  phenomena  about  which 


458  THE    SECONDARY   ENRICHMENT    OF    ORE-DEPOSITS. 

there  has  been  so  much  difference  of  opinion   among  those 
that  have  examined  them. 

Deposits  in  Arid  Regions. — De  Launay,  who  has  studied  the 
literature  of  Mexican  and  South  American  mines  very  exten- 
sively, makes  the  following  general  statement  as  to  the  average 
conditions  of  the  silver-ores  in  those  countries  from  the  surface 
downwards : 

' '  Near  the  surface  the  silver  in  the  veins  is  in  the  native  state,  with  chlorides, 
bromides,  iodides,  etc.,  associated  with  oxides  of  iron,  manganese  and  often  of 
copper ;  if  the  gangue  is  siliceous,  it  shows  a  honeycomb  aspect,  resulting  from 
the  removal  of  the  sulphides  which  it  formerly  held  ;  frequently  red  and  gray 
clays  are  associated  with  it.  These  ores  are  the  pacos,  cascajos,  colorados,  etc. ,  of 
the  Spanish-American  miners,  which  are  designated  by  the  general  term  metales 
calidos  (free  milling  ores),  but  whose  tenor  in  silver  is  often  small  compared  to  the 
rest  of  the  deposit. 

"  Lower  down,  at  about  80  to  150  meters,  appears  the  bonanza-zone  of  the  Mexi- 
cans, where  by  a  sort  of  phenomenon  of  cementation  is  concentrated  the  silver, 
coming  in  part  from  the  surface  (often  with  the  copper,  if  this  is  abundant  in  the 
deposit).  The  silver  is  here  in  the  state  of  sulphide  (Ag2S)  ;  the  copper  as  chal- 
cocite,  gray-copper  (itself  often  argentiferous)  and  bornite  ;  iron  is  wanting  or  is 
in  the  form  of  oxide  ;  lead,  not  abundant,  is  mostly  in  the  state  of  carbonate. 

"  Finally,  when  one  passes  below  the  hydrostatic  level,  which  is  rarely  lower 
than  400  or  5CO  meters,  one  finds  the  complex  vein-filling  of  sulphides,  antimon- 
ides  and  arsenides,  which  in  their  primitive  form  extend  indefinitely  in  depth  ; 
that  is,  one  has,  in  proportions  varying  with  different  deposits,  galena,  more  or 
less  argentiferous,  iron  and  copper  pyrites,  arsenopyrite,  blende,  etc.,  with  less 
abundant  silver-minerals." 

My  personal  observations  in  these  countries  have  been  very 
limited,  being  confined  to  a  few  weeks'  visit  in  Peru  and  the 
State  of  Chihuahua,  Mexico,  respectively.  In  Peru,  I  saw  a 
dull-black  copper-glance,  brought  from  the  famous  Cerro  de 
Pasco  mining-district,  where  silver-mining  has  been  extensively 
carried  on  for  centuries.  This  ore  is  said  to  be  found  wherever 
the  workings  have  been  carried  down  below  the  water-level, 
and  is  estimated  to  constitute  a  zone  of  great  extent  and  value 
beneath  all  the  old  workings.  It  is  evidently  a  concentration 
by  leaching  of  the  small  amount  of  copper  that  was  dissemi- 
nated through  the  now  oxidized  ores  above. 

In  Chihuahua,  I  had  no  opportunity  to  examine  the  silver- 
deposits  below  the  water-level ;  but  in  the  middle  levels  of  the 
mines,  at  200  to  300  feet  below  the  surface,  oxidized  and  un- 
altered sulphide  ore-bodies  were  not  infrequently  found  side 
by  side,  so  to  speak,  on  the  same  level.  *  The  former,  generally 


THE    SECONDARY    ENRICHMENT    OF    ORE-DEPOSITS.  459 

in  a  foot- wall  streak,  constitute  the  Colorado  ores  of  the  Mexican 
miners,  and  carry  rich  silver-minerals  in  a  red  clayey  material 
that  contains  rolled  fragments  of  quartz  and  ore,  and  is  evi- 
dently on  a  plane  of  movement  subsequent  to  the  mineralization. 
The  latter,  which  consist  of  pyrite,  galena  and  blende  in  a  dense 
hard  matrix,  occur  in  greater  bulk  than  the  richer  ores,  and  ap- 
parently owe  their  escape  from  oxidation  to  their  impenetra- 
bility to  surface-waters.  The  sulphide  is  so  much  lower  in 
grade  than  the  Colorado  ore,  that  it  was  generally  left  by  the 
early  miners,  and  now  constitutes  a  concentrating-ore.  Evi- 
dently the  foot-wall  streak,  which  often  opens  out  into  great 
"  bonanzas,"  was  enriched  by  the  leaching  of  such  parts  of  the 
other  ore  as  had  been  thoroughly  decomposed. 

In  Australia,  the  arid  climate  of  which  presents  similar  con- 
ditions to  those  found  in  Arizona,  Mexico  and  South  America, 
we  would  expect,  as  in  the  latter  regions,  to  find  abundant  evi- 
dence of  secondary  alteration  of  ore-deposits.  In  point  of  fact, 
the  descriptions  of  many  of  the  important  mines  of  that  region 
make  mention  of  phenomena  which  seem  to  be  most  readily 
explainable  on  this  theory,  although,  until  they  have  been  ex- 
amined with  this  end  in  view,  one  cannot  be  sure  how  far  all 
the  evidence  will  support  it.  In  the  famous  Broken  Hill  lode, 
as  described  by  Jaquet  in  the  memoirs  of  the  Geological  Sur- 
vey of  ]S"ew  South  Wales,  certain  occurrences  are  definitely 
described  by  him  as  secondary  sulphides.*  The  primary  sul- 
phide-ore is  an  intimate  mixture  of  argentiferous  galena  and 
zinc-blende,  with  quartz,  garnet  and  feldspar,  and  pyrite,  chal- 
copyrite,  arsenopyrite,  wulfenite  and  fluorite  as  accessory  con- 
stituents. These  ores  contain  on  an  average  5  to  36  oz.  of 
silver  per  ton,  7  to  50  per  cent,  of  lead,  and  14  to  30  per  cent, 
of  zinc.  Mr.  Jaquet  says  : 

"  Sulphide-ore,  secondary,  occurs  as  a  thin  layer,  varying  in  thickness  from  3 
inches  to  6  feet,  which  coats  the  ordinary  sulphides  at  all  points  where  dry  ore, 
rich  in  silver,  comes  in  contact  with  them.  Eesembling  soot  somewhat  in  appear- 
ance, it  has  been  named  '  sooty  sulphide-ore '  by  the  miners.  It  is,  without  doubt, 
ordinary  sulphide  ore  altered  and  enriched  by  contact  with  dry  ores." 

These  enriched  ores  carry  up  to  250  oz.  silver  per  ton  and  12 

*  Mem.  Geol  Sur.,  New  South  Wales,  Geology,  No.  5,  Sydney,  1894,  p.  88.  See 
also  Zeitschr.  Prak.  Geol,  vol.  v.,  p.  95.  1897. 


460  THE    SECONDARY    ENRICHMENT    OF    ORE-DEPOSITS. 

per  cent,  of  copper.  The  dry  silver-ores  are  the  antimonial  and 
arsenical  sulphides  of  silver,  polybasite,  stromeyerite,  dyscrasite, 
proustite,  pyrargyrite,  stephanite,  etc.,  which  occur  in  the  lower 
part  of  the  kaolin-ore  that  forms  the  bulk  of  the  oxidized  zone 
in  the  locality  described,  and  carries  oxidized  minerals  of  iron, 
manganese,  lead  and  copper.  This,  also,  is  of  much  lower  grade 
than  the  enriched  sulphide.  It  is  very  evident,  therefore,  that 
in  the  process  of  alteration  by  surface-agencies  the  oxidation 
products — especially  the  silver-  and  copper-combinations — have 
been  leached  down  and  redeposited  as  sulphides,  and  are  most 
abundant  in  contact  with  the  original  sulphides  of  the  deposit. 

It  does  not  appear  from  the  descriptions  that  the  enrichment 
has  extended  to  any  considerable  distance  below  the  contact- 
zone  of  altered  with  relatively  unaltered  material.  This  may 
be  due  to  the  absence  of  later  fractures  which  would  admit  the 
descending  solution ;  or  it  ma^  be  that  enrichments  do  exist 
which  have  not  yet  been  detected  through  want  of  systematic 
search. 

In  the  neighboring  Broken  Hill  Consols  mine,  as  described 
by  Mr.  George  Smith,*  there  is  evidence  of  still  more  exten- 
sive secondary  enrichment  of  sulphides,  the  silver-minerals 
being  mainly  in  the  rather  rare  and  unusually  rich  forms  of 
stromeyerite,  dyscrasite,  fahlerz  and  antimonial  silver  chloride. 
Although  occurring  in  the  same  country  rocks  as  the  main 
Broken  Hill  deposit,  instead  of  being,  as  in  that  case,  in  the 
form  known  as  "  saddle  reefs,"  which  conform  with  the  schis- 
tosity  and  are  of  great  size,  they  are  found  only  in  compara- 
tively narrow  veins  which  distinctly  cross  the  schistosity.  The 
vein  is  mineralized  only  at  the  intersection  of  what  is  known 
as  cross-veins,  and,  of  the  rich  silver-minerals  mentioned  above, 
some  "  have  not  been  met  with  in  the  lower  workings,  though 
each  has  been  found  at  some  distance  below  the  water-level;" 
while  those  that  are  found  at  greater  depth  occur  there  in 
smaller  quantities  and  "  have  been  found  to  assume  a  distinct 
track  and  are  evidently  the  continuation  of  the  larger  deposits 
worked  in  the  upper  levels."  The  so-called  cross-veins  are  de- 
scribed as  "  a  succession  of  rock-joints  formed  along  a  line  of 
weakness  and  enlarged  in  places  by  a  process  of  removal  and 

*  Trans.,  xxvi.,  69,  71,  73. 


THE    SECONDARY    ENRICHMENT    OF    ORE-DEPOSITS.  461 

replacement."  The  more  important  one,  which  is  figured  (p. 
73),  falls  vertically  on  the  lode  which  has  a  shallow  dip  near 
the  surface,  and  immediately  below  it  in  the  main  vein  is  an 
accumulation  of  stromeyerite,  dyscrasite  and  more  or  less  oxi- 
dized material  impregnated  with  silver  chloride.  The  cross- 
veins  carry  in  some  cases  blende  and  galena;  in  others  only 
pyrite. 

While  Mr.  Smith  has  recourse  to  secondary  concentration 
for  the  enrichment  of  the  oxidized  zone,  it  does  not  seem  to 
have  occurred  to  him  that  the  concentrations  of  rich  mineral 
below  this  zone  might  also  have  been  produced  by  solutions 
along  the  main  fissure  from  the  cross-veins.  He  brings  forward 
a  theory  of  electro-magnetic  currents  to  account  for  the  precipi- 
tation of  the  minerals  at  these  intersections. 

It  is  always  unsafe  to  theorize  on  the  observations  of  others ; 
but  in  the  present  case,  it  seems  legitimate  to  offer  the  sugges- 
tion that,  even  admitting  the  possibility  of  electric  action  as  a 
stimulant  to  the  chemical  reactions,  it  is  necessary  to  predicate 
previous  conditions  which  will  render  the  reactions  possible. 
In  the  case  of  these  cross-veins,  as  in  those  of  the  indicators  of 
Ballarat,  and  the  similar  fahlbands  of  Norway,  which  are  all 
zones  of  relatively  barren  pyritiferous  materials  crossing  the 
ore-bearing  veins,  it  seems,  in  a  general  way,  that  reactions  be- 
tween salts  of  the  metals  and  their  sulphides  have  been  the  un- 
derlying cause  of  the  concentration  of  the  more  valuable  metals 
at  or  near  the  intersection.  There  will  have  been  a  great  num- 
ber of  differing  conditions  in  such  districts,  or  groups  of  deposits, 
and  it  does  not  seem  absolutely  necessary  that  we  should  have 
recourse  to  descending  solutions  for  the  salts  of  the  metals  in 
every  case ;  they  may  have  been  contained  in  ascending  solutions. 
An  instance  where  it  seems  probable  that  there  has  been  enrich- 
ment from  ascending  salt-solutions  is  the  G-eyser  mine  at  Silver 
Cliff,  Colorado,*  where,  in  a  narrow  vein  at  2000  feet  in  depth, 
is  an  unusually  rich  and  very  recent-looking  body  of  sulphides 
of  silver,  lead,  zinc  and  copper.  The  ascending  waters  which 
issue  from  the  parallel  and  adjoining  fissures  are  highly  charged 
with  carbonic  acid,  and  carry,  apparently  in  the  form  of  car- 
bonates, small  amounts  of  the  metals  found  in  the  veins.  What- 

*  U.  S.  Geol.  Sur.,  17th  Ann.  Rep.,  Part  ii.,  p.  456. 


462  THE   SECONDARY   ENRICHMENT    OF    ORE-DEPOSITS. 

ever  may  have  been  the  original  form  in  which  the  metallic 
minerals  were  brought  to  this  deposit,  it  seems  evident  that  at 
the  present  day  they  must  be  coming  in  as  carbonates  and  be 
deposited  as  sulphides  in  contact  with  the  already  existing  sul- 
phides, thus  enriching  the  latter. 

SUMMARY. 

From  the  foregoing  geological  evidence,  which  could  be 
doubtless  very  much  enlarged,  it  appears  to  be  fairly  well  es- 
tablished : 

1.  That  descending  waters  not  only  cause   migrations,   or 
transference  and  reconcentration,  of  the  alteration  products  of 
the  original  vein-materials  in  oxidized  form,  producing  in  one 
place  an  enrichment,  and  in  another  possibly  an  impoverish- 
ment of  the  original  deposit,  but  that  in  their  further  down- 
ward course  the  oxidized  forms  are  frequently  reduced  and  re- 
deposited  as  sulphides,  thereby  producing  a  sulphide  enrich- 
ment of  the  original  vein-materials. 

2.  That  this  secondary  enrichment  of  sulphides  is  not  nec- 
essarily a  reduction  in  the  presence  of  organic  matter,  but  is 
frequent  where  no  organic  matter  can  be  supposed  to  be  pres- 
ent; it  occurs  mainly  in  contact  with  the  original  sulphides  of 
the  deposits,  and  is,  presumably,  a  result  of  chemical  reaction 
between  these  sulphides  and  the  materials  brought  down  in 
solution  by  the  descending  waters. 

3.  That  while  this  re-deposition  of  sulphides  in  many  cases 
appears  to  commence  at  or  near  the  groundwater-level,  it  does 
not  appear  to  have  a  necessary  connection  with  that  level,  and 
may  under  favorable  conditions  extend  below  that  level  for  a 
distance  as  yet  undetermined,  the  most  important  favoring  con- 
ditions appearing  to  be  recent  or  post-mineral  fractures,  which 
have  admitted  a  relatively  free  and  uninterrupted  descent  of 
these  waters. 

In  endeavoring  to  trace  back  the  processes  by  which  the 
results  have  been  brought  about,  it  is  important  to  bear  in 
mind  the  physical  changes  that  may  be  assumed  to  have  taken 
place  during  the  time  that  has  elapsed  since  a  given  ore-deposit 
was  originally  formed  and  before  it  reached  the  condition  in 
which  it  is  found  at  the  present  day.  These  changes  necessa- 
rily vary  with  each  mining  region  or  district,  being  in  some 


THE    SECONDARY    ENRICHMENT    OF    ORE-DEPOSITS.  463 

cases  very  considerable,  in  others  relatively  slight.  They  may 
be  classed  under  two  general  categories : 

First,  the  rock  shatterings  resulting  from  dynamic  force 
connected  with  earth-movements  or  eruptive  action.  These 
have  opened  channels  for  the  entrance  of  surface-waters  within 
the  rock-mass  and  thereby  extended  the  areas  to  tvhich  the 
chemical  actions  produced  by  the  latter  may  have  extended. 

Second,  the  erosion  or  denudation  to  which  the  region  has 
been  subjected,  and  which  has  gradually  worn  down  the  origi- 
nal surface  to  its  present  configuration.  As  a  result  of  this 
wearing  down  the  lower  parts  of  an  ore-deposit  have  been  con- 
tinually approaching  the  surface,  and  in  no  case,  probably,  is 
what  was  originally  the  superficial  portion  of  an  ore-deposit 
still  in  existence.  The  amount  of  the  wearing  away  is  not 
always  determinable,  but  it  may  have  been  very  large ;  thus,  at 
Leadville,  I  estimated  that  in  round  numbers  a  thickness  of 
about  10,000  feet  of  rocks  had  been  worn  away  in  order  to 
bring  the  ore-bodies  at  present  exposed  to  the  surface. 

In  the  Butte  district,  where  there  are  no  stratified  rocks, 
there  exists  no  criterion  by  which  to  estimate  accurately  the 
amount  of  denudation,  but  the  readily  disintegrable  character 
of  the  granite  country-rock  and  the  faulting  to  which  I  have 
already  alluded  show  that  it  must  have  been  very  considerable. 
There  the  ore-deposits  occurring  along  nearly  vertical  fissures, 
and  the  later  shattering  having  produced  extraordinarily 
abundant  secondary  fissures  nearly  coincident  with  the  earlier 
ones,  the  conditions  were  unusually  favorable  for  an  abundant 
leaching  down  of  the  material  taken  up  in  solution  by  the  sur- 
face-waters. As  the  surface  gradually  lowered  we  may  con- 
ceive that  the  insoluble  materials  were  carried  off  mechanically ; 
of  the  soluble  minerals,  however,  but  a  relatively  small  propor- 
tion would  have  been  removed  by  the  actual  surface  run-off. 
The  greater  portion  would  have  been  carried  back  to  lower 
levels  before  they  came  near  enough  to  the  actual  surface  to  be 
taken  up  in  the  run-off'. 

It  will  aid  our  conception  to  divide  the  veins  theoretically 
into  three  horizontal  zones.  The  upper-  or  surface-zone,  that 
which  immediately  adjoins  the  present  surface,  is  necessarily 
the  zone  of  highest  and  most  recent  oxidation.  Any  sulphides 
found  in  it  will  simply  be  residual  masses  which,  for  some 


464  THE    SECONDARY   ENRICHMENT   OF    ORE-DEPOSITS. 

reason,  the  oxidation  has  not  completely  penetrated.  The 
changes  which  have  taken  place  in  this  zone  will  have  been 
mainly  of  removal,  rarely  of  addition,  and  any  enrichment  that 
will  have  come  about  in  this  zone  will  have  been,  as  a  rule,  dif- 
ferential, resulting  from  the  greater  proportion  of  valueless  or 
base  metals  removed. 

The  second  or  intermediate-zone  may  be  called  the  zone  of 
oxide-enrichment.  In  this,  the  less  soluble  or  more  readily 
precipitable  metals  which  have  been  brought  down  from  the 
zone  above,  are  found  as  carbonates  or  oxides,  or  in  some  cases 
as  native-metals. 

The  third  zone  may  be  called  the  zone  of  sulphide-enrich- 
ment, in  which  the  materials  brought  down  in  solution,  and 
not  deposited  in  the  zone  next  above,  are  deposited  as  sulphides 
(also  as  sulph-arsenides  and  sulph-antimonides)  or  in  some  cases 
as  native-metals  in  contact  with  the  original  sulphides  of  the 
deposit. 

The  presence  of  organic  matter  would  hasten  the  reduction 
to  sulphide,  and  might  cause  the  deposition  of  the  latter,  under 
favorable  conditions,  even  at  the  surface,  but  it  should  be  con- 
sidered as  an  accidental,  rather  than  an  essential  occurrence. 

These  zones  are,  as  has  been  said,  a  theoretical  conception ; 
in  practice  they  are  rarely  well-defined,  and  in  many  cases  one 
or  more  may  be  wanting.  One  will  run  into  the  other,  and,  as 
denudation  progresses,  a  lower  zone  is  slowly  changing  to  the 
one  next  above  it;  thus,  as  time  goes  on, it  will  be  a  constantly 
richer  zone  that  rises  to  the  surface  to  be  oxidized,  and  has  part 
of  its  oxidation  products  carried  back  and  re-deposited  either  as 
oxides  or  sulphides.  Hence,  other  things  being  equal,  the 
longer  a  deposit  has  been  subjected  to  denudation  the  greater 
will  be  the  enrichment  below  the  surface-zone.  The  rate  of 
denudation  may  also  have  influence  upon  the  amount  of  enrich- 
ment, for  it  can  be  conceived  that  the  surface-rocks  may  be  so 
readily  disintegrable  and  the  rate  of  erosion  under  favoring 
climatic  conditions  may  be  so  rapid,  that  the  surface-removal  of 
the  oxidized  material,  both  mechanical  and  chemical,  may  pro- 
ceed so  much  faster  than  the  downward  seepage  along  the 
plane  of  the  ore-deposit,  that  little  or  no  enrichment  of  the  in- 
terior portion  of  the  deposit  may  have  taken  place. 

Such  a  rapid  denudation  may  be  conceived  to  have  taken 


THE    SECONDARY    ENRICHMENT    OF    ORE-DEPOSITS.  465 

place  on  exposed  points  during  the  ice-invasion  of  the  glacial 
period,  at  which  time,  moreover,  under  the  low  surface-tem- 
peratures chemical  decomposition  would  have  been  relatively 
sluggish.  In  arid  regions,  on  the  other  hand,  where  the  great 
heat  would  render  chemical  decomposition  more  energetic,  and 
where  there  has  been  not  only  no  ice-action,  but  also  compara- 
tively little  erosion  by  water  to  wear  down  the  surface,  we 
should  expect  the  zone  of  oxide-enrichment  to  extend  down  to 
great  depths,  but  if  the  aridity  were  so  great  that  there  was 
very  little  water  percolating  through  the  rocks  in  depth,  there 
might  be  but  little  sulphide-enrichment. 

Chemical  Processes  Involved. — I  do  not  feel  prepared  to  dis- 
cuss in  detail  the  chemical  processes  that  are  involved  in  the 
changes  which  are  shown  to  have  taken  place  by  the  above 
quoted  observations.  They  necessarily  vary  from  one  deposit  to 
another  under  the  varying  mineralogical  and  physical  condi- 
tions that  prevail  in  each  place.  Moreover,  the  chemical  re- 
actions that  are  suggested  by  previous  investigations  should  be 
tested  experimentally  before  any  one  can  state  with  any  degree 
of  confidence  what  the  succession  of  chemical  processes  in  a 
given  case  has  been ;  for  these  investigations  have  generally 
been  conducted  with  another  object  in  view,  or  with  a  different 
conception  of  the  actual  conditions  in  nature. 

Mr.  Weed,  in  his  paper  already  cited,  has  given  quite  full 
quotations  from  all  the  authorities  that  bear  upon  this  subject, 
and  I  shall,  therefore,  not  repeat  them,  but  only  give  a  brief 
general  statement  of  the  main  processes  that  may  be  supposed 
to  have  contributed  to  the  mineralogical  conditions  that  are 
found  in  the  ore-deposits  cited  above,  laying  more  stress  on 
the  natural  occurrences  that  illustrate  the  actual  changes. 

The  most  common  sulphide-minerals  in  original  ore-deposits 
are  the  iron  sulphides,  pyrite,  marcasite,  pyrrhotite,  chalco- 
pyrite  and  arsenopyrite ;  and  next  to  these,  galena,  zinc-blende 
and  various  copper  sulphides.  While  there  is  a  great  variety 
of  other  metallic  compounds  in  ore-deposits,  yet  in  most  deposits 
the  greater  bulk  is  so  far  formed  by  one  or  more  of  the  above 
minerals  that  the  chemical  changes  will  be  largely  governed  by 
the  reactions  to  which  these  appear  to  be  subject.  Of  these 
sulphides  marcasite  is  the  most  readily  decomposed,  while 
pyrite,  if  occurring  by  itself  in  pure  crystals,  often  proves  very 


466  THE    SECONDARY   ENRICHMENT    OF    ORE-DEPOSITS. 

resistant  to  alteration.  Where  there  are  mixed  sulphides,  how- 
ever, the  oxidation  is  observed  to  proceed  more  rapidly  and  all 
are  readily  attacked. 

The  actual  changes  observed  by  me  in  a  great  body  of  pyrite 
carrying  galena  in  a  limestone  country-rock,  which  had  under- 
gone partial  decomposition  from  the  periphery  inwards,  are 
as  follows  :*  The  original  fresh  pyrite  or  marcasite  crystals  are 
first  disintegrated  and  slightly  pitted  on  the  surface,  then 
changed  to  melanterite  or  hydrated  ferrous  sulphate  and  the 
galena  becomes  anglesite.  In  the  outer  or  more  fully  oxidized 
zone  the  iron-vitriol  has  changed  in  part  to  yellow  basic  sul- 
phate ;  in  part  to  limoiiite  with  a  separation  of  native  sulphur. 

The  theoretical  changes  that  are  assumed  to  take  place  by 
the  action  of  waters  carrying  oxygen  or  oxidizing  agents  are : 
first,  an  alteration  of  the  iron  sulphide  to  ferrous  sulphate  with 
the  formation  of  sulphuretted  hydrogen  and  sulphur  which 
may  have  oxidized  to  sulphuric  or  sulphurous  acid.  By  further 
oxidation  the  ferrous  sulphate  will  become,  in  part  at  least, 
ferric  sulphate,  and  this  in  its  turn  will  react  upon  the  remaining 
ferrous  sulphate,  or  upon  the  sulphides,  and  form  more  ferrous 
sulphate  or  sulphates  of  the  other  metals  which  are  present. 
By  this  cycle  of  reactions  a  supply  of  both  ferric  and  ferrous 
sulphates  would  seem  to  be  provided  in  the  oxidized  zone,  but 
the  extending  downwards  of  the  ferric  salts  would  decrease  as 
the  supply  of  oxygen  in  the  waters  became  less  abundant. 

It  may  be  assumed  that  the  sulphates  of  the  metals  thus 
formed  would  be  transported  for  greater  or  less  distances,  gener- 
ally in  proportion  to  their  solubility,  the  iron  sulphates  being 
the  most  soluble ;  next,  those  of  copper  and  zinc ;  silver  sul- 
phate is  less  soluble  and  also  more  readily  decomposed,  while 
lead  sulphate  is  extremely  insoluble. 

This  accords  with  the  facts  generally  observed  in  nature. 
Thus,  from  the  gossan,  which  is  generally  a  porous  siliceous 
mass  stained  by  the  limonite  or  hematite  resulting  from  the  de- 
composition of  part  of  the  iron  sulphate,  the  copper-  and  zinc- 
salts  may  have  been  more  or  less  completely  removed  or  trans- 
formed to  less  soluble  carbonates  and  silicates.  Where  galena 
has  been  present  in  considerable  amount  the  sulphate  (angle- 
site)  is  generally  found  quite  near  the  surface  or  forming  a  coat- 

*  Proc.  Colo.  Sei.  Soc.,  vol.  ii.,  p.  104. 


THE   SECONDARY    ENRICHMENT    OF    ORE-DEPOSITS.  467 

ing  around  residual  masses  of  galena  which  some  think  it  has 
protected  from  oxidation.  Where  carbonate  of  lime  is  present, 
as  in  limestone  deposits,  it  is  transformed  to  the  carbonate 
(cerussite)  which  is  more  soluble,  especially  in  the  presence 
of  an  excess  of  carbonic  acid,  and  may  be  transported  from  its 
original  location  and  concentrated  in  bonanzas  of  more  or  less 
crystalline  mineral.  The  silver  sulphate  formed  near  the  surface 
is  generally  transformed  to  the  chloride,  but  is  not  infrequently 
reduced  to  the  native  state.  Gold  probably  does  not  form  a 
sulphate,  but  when  combined,  as  in  the  form  of  the  telluride, 
is  dire"ctly  reduced  to  the  metallic  state.  It  is,  however,  to  a 
certain  extent  soluble  in  ferric  sulphide,  and  would  in  part  be 
transported  by  this  solution  until  it  is  precipitated  by  the  reduc- 
tion of  the  ferric  to  the  ferrous  condition  which  may  occur  in 
contact  with  the  sulphide  or  with  ferrous  salts. 

Under  certain  conditions  ferric  sulphate  will  decompose  the 
metallic  sulphides  with  the  formation  of  ferrous  salts  and  sul- 
phates of  the  metals ;  possibly  also  with  a  solution  of  part  as 
sulphides.  Actual  test  has  shown  that  it  acts  with  great  readi- 
ness on  the  iron  sulphides,  but  much  more  slowly  on  silver  sul- 
phides. The  action  of  copper  sulphide  has  not  been  tested,  but 
is  probably  intermediate  between  the  two. 

It  would  naturally  be  expected  that  the  oxygen  included  in 
surface-waters  would  gradually  be  eliminated  with  depth,  and 
Lepsius*  has  shown  by  actual  experimental  tests  of  waters  taken 
from  bore-holes  that  there  is  a  gradual  and  fairly  uniform  de- 
crease of  contained-oxygen  in  the  waters  with  depth.  The 
oxygen  would  be  more  rapidly  exhausted  in  a  region  of  active 
chemical  action,  such  as  an  ore-deposit  in  process  of  alteration ; 
hence  it  may  be  assumed  that  in  each  case  there  will  be  a  cer- 
tain depth  at  which,  owing  to  the  absence  of  free  oxygen,  the 
general  tendency  in  the  reactions  which  take  place  will  be  re- 
ducing rather  than  oxidizing,  and  when  no  organic  matter  is 
present  we  must  look  to  the  original  sulphide  minerals  to  fur- 
nish the  necessary  agents  for  reducing  the  sulphates  to  sul- 
phides again,  or  to  the  native  state. 

The  most  pertinent  investigations  bearing  upon  the  reactions 
that  would  take  place  are  those  undertaken  by  E.  F.  Anthonf 

*  Ber.  d.  Deutsch.  Chem.  Gesdlschft. ,  vol.  xviii.,  p.  2487.     1885. 
f  Jour.f.  Prak.  Chem.,  vol.  x.,  No.  6,  p.  353. 

30 


468  THE    SECONDARY   ENRICHMENT    OF    ORE-DEPOSITS. 

in  1837",  primarily  for  facilitating  analytical  work  in  the  labora- 
tory, which  were  continued  later  on  the  same  lines  by  E. 
Schiirmann,*  for  which  reason  they  are  generally  known  as 
the  "  Schurmann  "  reactions.  By  these  it  was  established  that 
in  the  presence  of  the  sulphides  of  certain  of  the  metals  the 
salts  of  other  metals  would  be  decomposed  and  the  metal  pre- 
cipitated as  sulphide,  indicating  thus  that  the  latter  metal  pos- 
sesses a  greater  affinity  for  sulphur  than  the  former,  and  thus 
the  following  series  of  the  more  common  metals  was  established 
in  the  order  of  their  affinity  for  sulphur:  Mercury,  silver, 
copper,  bismuth,  cadmium,  antimony,  tin,  lead,  zinc,  nickel, 
cobalt,  iron,  arsenic,  thallium,  and  manganese.  In  other  words, 
a  salt  of  any  metal  in  the  series  would  be  decomposed  by  the  sul- 
phide of  any  succeeding  metal,  and  the  first  metal  precipitated 
as  sulphide.  Thus,  from  silver-  or  copper-salts  the  metal  would 
be  precipitated  as  sulphide  by  lead,  zinc,  or  iron  sulphides. 

Sulphuretted  hydrogen  is  an  important  agent  for  the  precipi- 
tation of  metallic  sulphides,  and  this  is  not  infrequently  found 
in  mine-waters.  It  is  assumed  to  be  given  oft  in  the  deposition 
of  the  various  forms  of  pyrite,  and  qualitative  tests  in  the  lab- 
oratory of  the  Survey  have  shown  that  it  is  evolved  in  the 
treatment  of  pyritous  ores  by  very  dilute  sulphuric  acid,  though 
less  freely  with  pure  pyrite  than  with  mixed  sulphides. 

Ferrous  sulphate  will  also  precipitate  many  of  the  metals 
from  their  solutions  in  the  native  state ;  possibly  in  some  cases 
as  sulphides  with  the  formation  of  ferric  sulphate,  and  it  is 
probable  that  other  ferrous  combinations  will  act  in  a  similar 
manner.  .Thus,  in  the  mines  of  Kongsberg,  Norway,  which  are 
remarkable  for  the  abundance  of  native-silver  below  the  water- 
level,  Vogtf  assumes,  for  the  occurrences  of  the  metal,  as  it  is 
sometimes  found  in  fine  cracks  in  the  country-rock  and  even  in 
garnets,  that  it  has  been  precipitated  from  its  solution  through 
the  reducing  action  of  ferrous  silicates. 

The  reaction  of  ferrous  sulphate  on  a  solution  of  silver-salt  is 
easily  tested  in  the  laboratory.  The  silver  is  readily  precipi- 
tated in  the  metallic  state  and  the  solution  colored  brown  by 
the  ferric  sulphate  formed.  With  an  excess  of  ferrous  sulphate 
present,  as  near  the  out-crop  of  ore-deposits,  this  might  account 

*  Liebig's  Ann.  d.  Chem.,  vol.  249\  1888,  pp.  326-350. 
f  Jour.f.  Prak.  GeoL,  April,  1899,  p.  118. 


THE    SECONDARY    ENRICHMENT    OF    ORE-DEPOSITS.  469 

for  the  separation  of  native-silver  from  silver-salts,  while  on  the 
other  hand  with  an  excess  of  ferric  oxide  the  silver  might  be 
carried  further  down  in  solution. 

In  the  copper-deposits,  to  which  my  studies  have  been  more 
especially  directed,  one  often  finds  a  black  sooty  alteration 
product  in  pyritous  ores  just  at  the  water-level  which  it  has 
been  the  custom  to  call  an  "  oxysulphuret,"  but  which,  so  far 
as  tested,  has  always  proved  to  be  amorphous  copper-glance. 
It  is  evidently  a  very  recent  formation  and  it  might  be  reasoned 
that  it  has  not  yet  had  time  to  become  crystalline.  On  the 
other  hand,  chalcopyrite  is  by  some  considered  to  be  a  com- 
pound of  cuprous  sulphide  (Cu2S)  and  ferric  sulphide  (Fe.2S3)  as 
bornite  is,  in  a  similar  way,  considered  to  consist  of  cuprous 
(Cu.,S)  and  cupric  (CuS)  sulphides  with  ferrous  sulphide  (FeS). 
In  the  attack  by  a  solution  of  ferric  sulphide  the  iron  molecule 
would  first  be  removed,  and  in  the  case  of  chalcopyrite  the 
Cu2S  might  be  left  in  the  amorphous  powder  above  noted.  If, 
however,  the  attack  was  continued  until  copper  sulphate  was 
formed,  this  being  precipitated  either  by  sulphuretted  hydrogen 
or  in  contact  with  unaltered  sulphide,  by  analogy  with  results 
obtained  in  the  laboratory  the  precipitated  sulphide  would  be  a 
black  amorphous  powder.  Such  a  precipitate  was  obtained  by 
A.  P.  Brown*  by  the  action  of  powdered  pyrite  on  a  neutral 
solution  of  copper  sulphate  under  pressure  during  his  investi- 
gations, by  which  he  proved,  as  he  assumed,  that  marcasite  is 
largely  composed  of  the  ferrous  sulphide,  and  pyrite  contains 
more  ferric  sulphide. 

Bischoff  states  that  the  amorphous  precipitates  from  solu- 
tion by  sulphuretted  hydrogen  gradually  assume  a  metallic 
luster  and  tend  to  become  crystalline  when  extremely  dilute  solu- 
tions are  used  and  the  reagent  is  passed  sufficiently  slowly  over 
the  precipitates.  In  other  words,  under  conditions  more  nearly 
approaching  those  that  may  be  assumed  to  exist  in  nature. 

In  recent  years  Dr.  C.  Doelter  has  made  a  series  of  synthet- 
ical experiments  in  which,  by  treating  metallic  salts  by  sulphu- 
retted hydrogen  solutions,  he  has  succeeded  in  producing  in  crys- 
talline form  most  of  the  common  sulphide  minerals:  namely,  py- 
rite, chalcopyrite,  bornite,  chalcocite,  covellite,  galena,  bournon- 

*  Proc.  Amer.  Philos.  Soc.,  vol.  xxxiii.,  No.  145,  p.  240.     1894. 

f  Lehrbuch  d.  Cham.  u.  Phys.  Geol.,  Second  edition,  Bonn,  1866,  vol.  iii.,  p.  721. 


470  THE   SECONDARY   ENRICHMENT   OF    ORE-DEPOSITS. 

ite,  miargyrite,  jamesonite*  and  pyrrhotite.f  The  experiments 
were  conducted  at  moderately  elevated  temperatures ;  generally 
about  100°  C.  Such  temperatures  are  used  in  the  laboratory  to 
hasten  the  chemical  action,  but  it  is  probable  that  the  same 
effects  would  be  produced  at  the  ordinary  temperatures,  such  as 
would  be  found  in  ore-deposits,  if  sufficient  time  could  be  allowed. 
In  nature  it  is  probable  that  changes  in  temperature  may  have 
been  an  important  factor  in  producing  solution  or  precipitation 
of  minerals,  for  it  has  been  found  that  a  mineral-salt  which  was 
taken  up  in  solution  at  a  given  temperature  is  sometimes  rede- 
posited  under  a  change  in  temperature. 

More  significant,  however,  than  laboratory  experiments,  are 
the  synthetical  processes  of  nature,  which,  as  shown  by  Daubree 
and  other  European  geologists,  have  been  detected  in  the  many 
thermal  springs,  where  Roman  metals  and  coins  of  copper  and 
other  metals  have  lain  for  centuries  subjected  to  the  action  of 
waters  containing  feeble  solutions  of  mineral  sulphates.  Among 
the  minerals  thus  formed  crystals  of  tetrahedrite,  chalcocite, 
bornite,  chalcopyrite  and  others  have  been  recognized.  At  the 
Springs  of  Bourbon  l'Archambault,J  the  succession  of  mineral 
coatings  around  the  metallic  copper  of  the  coin  is  the  exact  re- 
verse of  the  series  which  has  been  noted  above  in  copper-mines 
as  the  normal  change  in  waters  by  secondary  changes ;  namely, 
next  the  metallic-copper,  first,  black  copper-glance ;  then  bor- 
nite ;  then  chalcopyrite. 

That  the  reactions  necessary  to  produce  these  changes  have 
taken  place  in  nature  in  a  certain  regular  series  is,  in  itself,  fair 
ground  for  assuming  that  under  possible  variations  of  condi- 
tions, the  same  changes  might  take  place  in  reversed  order ;  for 
it  is  recognized  by  modern  chemists  that  the  reactions  between 
two  substances  which  produce  two  other  substances  are  part  of 
a  tendency  to  establish  a  condition  of  equilibrium,  as  it  is  called, 
between  the  substances  involved,  and  that  this  tendency  can  be 
modified  by  different  conditions  of  concentration,  temperature, 
pressure,  etc.,  so  that  it  is  conceivable  that  the  reaction  will 
proceed  in  one  direction  under  one  set  of  conditions,  and  in 
the  reverse  direction  under  another. 

*  Zeitsch.f.  Krystallogr.  u.  Mineral.,  vol.  xi.,  p.  40. 

f  Miner,  u.  Petrog.  Mitth.  v.  Tschermak,  vol.  vii.,  p.  535. 

J  Comptes  Rendus,  vol.  Ixxx.,  January-June,  1875,  p.  1297. 


THE    SECONDARY    ENRICHMENT    OF    ORE-DEPOSITS.  471 

I  am  indebted  to  Mr.  H.  1ST.  Stokes  of  the  U.  S.  Geological 
Survey  for  the  following  concise  statement  of  the  present  views 
of  chemists  on  this  subject : 

"  It  is  now  generally  recognized  by  physical  chemists  that  no 
reaction  is  complete  in  the  sense  expressed  by  chemical  equa- 
tions. Every  reaction  tends  to  a  condition  of  equilibrium  lying 
between  the  two  extremes ;  sometimes  at  an  appreciable  dis- 
tance from  both ;  sometimes  so  close  to  one  that  for  practical 
purposes  the  reaction  may  be  regarded  as  complete.  This  con- 
dition of  equilibrium  may  be  varied  as  follows : 

"  (1)  By  an  increase  of  the  relative  concentration  of  one  of  the 
terms  of  the  equation  which  tends  to  shift  equilibrium  to  the 
other  side.  This  may  be  effected  either  by  relative  concentra- 
tion of  one  term  on  the  same  side,  or  by  removing  the  reaction 
products  as  fast  as  formed. 

"  (2)  By  an  increase  of  temperature  which,  besides  increasing 
the  reaction-velocity,  shifts  the  equilibrium  more  or  less,  and 
always  toward  that  side  of  the  equation  which  contains  the  most 
energy.  The  reaction  velocity  is  the  speed  at  which  the  system  ap- 
proaches equilibrium.  In  some  cases  this  is  immeasurably  great, 
in  others  so  small  as  to  require  ages.  It  is  always  more  rapid 
at  first,  slowing  down  as  the  reaction  approaches  equilibrium. 

"(3)  By  increaseof  pressure  which  shifts  the  equilibrium  towards 
that  side  of  the  equation  which  naturally  occupies  less  volume. 

"  (4)  By  substances  foreign  to  the  reaction  which  may  retard 
or  accelerate  the  reaction  velocity,  without,  however,  influenc- 
ing the  final  state  of  equilibrium  (catalytic  action)." 

A  practical  instance  of  the  reversal  of  the  direction  of 
chemical  reaction  is  furnished  in  Yogt's*  description,  already 
cited,  of  the  famous  silver-mines  of  Kongsberg,  Norway.  In 
these  mines  silver  is  in  actual  bulk  the  predominating  metal. 
As  mined,  it  is  found  mainly  in  the  native  state  and  very  largely 
as  wire-silver.  This  wire-silver,  Yogt  proves  quite  conclu- 
sively, is  the  result  of  alteration  from  silver-glance  (argentite). 
He  gives  drawings  of  specimens  in  which  the  native  silver  is 
found  growing  out  of  a  base  of  silver-glance,  and  in  some  in- 
stances still  retaining  small  particles  of  glance  on  the  ends  of  the 
wires.  On  the  other  hand,  some  instances  are  found  where  the 

*  Op.  eft.,  p.  119. 


472  THE    SECONDARY    ENRICHMENT    OF    ORE-DEPOSITS. 

wire-silver  has  been  later  changed  back  to  silver-glance,  the  lat- 
ter retaining  the  form  of  the  wire-silver.  Thus,  three  processes 
are  shown  in  the  same  mine ;  the  original  deposition  as  glance ; 
the  change  from  glance  to  native-silver,  and  the  reversal  of  this 
process  in  the  change  from  native  silver  back  to  silver-glance. 

Conclusions. — Until  a  much  larger  number  of  ore-deposits 
have  been  studied  with  a  definite  purpose  of  determining  how 
far  they  have  been  subjected  to  secondary  enrichment,  it  does 
not  seem  safe  to  draw  any  far-reaching  conclusions  from  the  ob- 
servations and  suggestions  noted  above.  It  has  long  been  recog- 
nized that  the  superficial  alteration  of  ore-deposits  has  often  pro- 
duced a  very  considerable  modification  of  the  original  constitu- 
tion of  the  deposit,  and  its  alteration  has  so  frequently  been  in  the 
nature  of  an  enrichment  in  the  more  valuable  metals  relatively  to 
the  original  tenor  of  the  ores  that  it  has  given  rise  to  the  very 
hasty  decision  that  all  ore-deposits  necessarily  become  poorer  in 
depth,  which  is  almost  as  unjustifiable  as  the  old  assumption  by 
the  miner,  that  the  nearer  he  got  to  the  source  of  his  ore  in  the 
unknown  depths,  the  richer  it  would  become. 

The  fact  that  ores  under  some  conditions  may  be  removed 
and  re-deposited  as  sulphides,  even  below  groundwater-level, 
opens  a  wide  field  of  possibility  in  accounting  for  the  unusually 
rich  bodies  of  ore  that  are  in  some  mines  found  in  the  middle 
levels,  and  have  been  fruitlessly  sought  for  at  greater  depth. 
In  many  cases  these  have  undoubtedly  resulted  from  a  concen- 
tration of  material  leached  down  from  the  upper  portions  of  the 
deposit  as  they  have  been  gradually  worn  down 'and  carried 
away  by  denudation.  Especially  in  the  case  of  large  bodies 
of  pyritous  ore  carrying  small  proportions  of  more  valuable 
metals,  is  a  concentration  of  those  metals  by  downward  per- 
colating solutions  to  be  looked  for.  It  is,  however,  not  yet 
safe  to  say  that  all  rich  bonanzas  in  vein  deposits  have  neces- 
sarily been  formed  in  this  way. 

Although  not  yet  supported  by  definite  evidence,  the  im- 
pression is  very  strong  with  me  that  not  infrequently  the 
ascending  currents  have  also  produced  migrations  of  already 
formed  deposits  and  local  enrichments  under  favoring  conditions. 
What  these  conditions  are,  and  what  are  the  criteria  by  which 
they  may  be  distinguished  from  concentrations  by  descending 
waters,  it  remains  for  future  investigations  to  determine. 


ENRICHMENT    OF    GOLD   AND    SILVER   VEINS.  478 


The  Enrichment  of  Gold  and  Silver  Veins.* 

BY  WALTER  HARVEY  WEED,   BUTTE,    MONT. 

(Washington  Meeting,  February,  1900.) 

INTRODUCTION. 

IN  a  previous  paper  upon  the  enrichment  of  mineral  veins  by 
later  metallic  sulphides,  f  the  writer  has  shown  that  certain 
masses  of  rich  ores,  such  as  are  found  in  many  mines,  either 
near  the  water-line  or  as  bonanzas  in  depth,  are  of  secondary 
origin,  and  are  due  to  a  leaching  of  lean  ore  and  the  concentra- 
tion of  the  material  by  reaction  between  the  solution  and  the 
unaltered  ore  below.  The  geological  and  mineralogical  evi- 
dence is  believed  to  form  an  adequate  basis  for  a  chemical  and 
physical  explanation  of  the  phenomenon.  In  the  present  paper 
the  writer  will  give  a  brief  synopsis  of  this  theory,  and  will 
apply  it  more  particularly  to  deposits  of  the  precious  metals, 
laying  special  emphasis  upon  the  dependence  of  such  enrich- 
ments upon  the  presence  of  iron  sulphide  (as  pyrite,  etc.)  in 
the  primary  ore,  and  upon  structural  features  which  control 
the  circulation  of  the  enriching  solutions  below  the  water-level. 
It  is  believed  that  many,  though  not  all,  of  the  bonanzas  and 
pay-shoots  of  rich  sulphide  ores,  especially  those  carrying  gold 
and  silver,  which  are  encountered  in  ore-deposits,  are  of  such 
secondary  origin.  Apparently  it  is  essential  that  the  occur- 
rence and  structural  relations  of  such  ore-masses  should  be  un- 
derstood, as  the  success  of  the  mine  is  often  dependent  upon 
the  finding  and  extraction  of  these  ores.  A  legitimate  deduc- 
tion, too,  is  that  such  ore-deposits  decrease  in  value  with 
depth. 

As  my  own  studies  have  been  mainly  in  Montana,  my  illus- 
trations must  be  drawn  from  the  ore-deposits  of  this  and  ad- 
jacent States,  with  such  as  I  have  noted  in  hurried  visits  else- 
where. The  literature  of  ore-deposits  doubtless  affords  also 

*  Published  by  permission  of  the  Director  of  the  U.  S.  Geological  Survey, 
f  Bulletin  Geological  Society  of  America,  vol.  xi.,  pp.  179-206,  1900. 


474  ENRICHMENT    OF    GOLD    AND    SILVER    VEINS. 

many  illustrations  of  secondary  deposition  besides  those  quoted 
by  me  in  this  paper.  The  recognition  of  secondary  enrich- 
ment as  a  factor,  and  the  chief  one,  in  the  genesis  of  many  rich 
ore-deposits  was  forced  upon  me  several  years  ago  by  my  study 
of  the  Neihart,  Mont,  silver-gold  veins.  Since  then  it  has 
proved  to  be  of  frequent  occurrence  in  many  mines,  and  its 
study  has  led  me  to  the  theory  of  secondary  enrichment  pro- 
pounded in  a  previous  paper,  and  especially  applied  to  precious 
metals  in  this  paper. 

STATEMENT  OF  THE  PROBLEM. 

The  fact  that  masses  of  very  rich  ore  often  occur  near  the 
water-line  in  many  mines,  but  do  not  continue  in  depth,  and 
the  occurrence  of  pay-streaks  and  bonanzas  in  deep  mine-work- 
ings, is  a  matter  of  history  in  many  regions.  The  problem  is 
to  explain  the  genesis  of  such  ores.  The  theory  here  presented 
accounts  for  such  ores  as  enrichments  formed  from  bodies  of 
lean  ore  of  complex  composition,  which  have  been  lixiviated, 
the  gold,  silver  and  copper  being  carried  downward  below  the 
water-level  and  precipitated  as  high-grade  sulphide  ores.  The 
evidence  is  mainly  mineralogical  and  geological ;  but  it  is  in 
entire  accord  with  chemical  tests  and  reactions,  which  have 
been  carried  out  in  the  laboratory  or  are  too  well  known  to  be 
called  into  question. 

Surface-waters  are  believed  to  be  commonly  the  means  by 
which  the  lean  ores  are  leached  and  the  metallic  contents  car- 
ried down  and  redeposited.  In  some  cases,  however,  concen- 
tration has  probably  been  effected  by  new  fractures,  resulting, 
in  the  cases  known  to  the  writer,  from  later  volcanic  activity 
and  faulting,  and  serving  as  channels  for  upcoming  hot  waters. 
As  commonly  understood,  "  surface-waters "  are  those  which 
have  so  recently  left  the  surface  as  to  still  retain  constituents 
common  to  waters  now  found  at  or  near  the  surface  (free  car- 
bonic acid,  organic  acids,  chlorides,  etc.),  and  which  produce  an 
oxidation.  Thus  the  effect  of  superficial  alteration,  as  described 
by  most  writers,  has  been  the  production  of  carbonates,  chlor- 
ides, oxides,  etc.  In  those  instances  where  surface-agencies 
have  had  a  reducing  effect,  it  has  been  commonly  ascribed  to 
organic  matter,  though  Penrose  cites  the  formation  of  native 
copper  by  the  action  of  "  a  ferrous  salt  on  certain  copper  salts," 


ENRICHMENT    OF    GOLD    AND    SILVER    VEINS.  475 

as  an  instance  where  the  primary  chemical  action  is  one  of 
partial  oxidation,  and  the  reducing  action  follows,  as  the  effect 
of  one  of  the  partially  oxidized  compounds  on  the  other.  In 
this  sentence  lies  the  pith  of  the  whole  subject  of  enrichment, 
since  when  the  leaching  of  lean  ore  is  performed  by  oxidizing 
surface-waters  the  resulting  solutions  percolate  downward  as 
deoxidized  waters,  carrying  soluble  salts  that  are  the  result  of 
oxidation,  and  enrichment  is  the  result  of  a  reaction  between 
these  substances  in  solution  and  the  unaltered  ore  with  which 
they  come  in  contact  in  their  downward  course.  Above  the 
ground -water  level  there  is  a  constant  movement  of  the  water 
downward,  but  below  that  level  the  free  oxygen  has  commonly 
been  used  up.* 

THE  ZONES  OF  WEATHERING,  OF  ENRICHMENT,  AND  OF 
PRIMARY  SULPHIDES. 

At  the  outset  a  sharp  distinction  must  be  drawn  between  the 
secondary  or  later  enrichment  herein  described,  which  occurs 
in  part  at  the  water-level  but  usually  below  it,  and  the  enrich- 
ment due  to  simple  weathering  or  superficial  alteration  of  the 
ore.  In  the  latter  case  the  gold  or  other  values  remain,  while 
the  worthless  constituents  are  in  large  part  removed,  thereby 
greatly  increasing  the  value  per  ton  of  the  weathered  part  of 
the  vein.  This  process,  usually  known  as  superficial,  is  a  com- 
mon and  now  well-known  feature  of  ore-deposits  the  world 
over. 

In  order  to  describe  the  different  parts  of  veins  here  under 
discussion,  the  writer  will  follow  common  usage  in  calling  the 
upper  weathered  part  the  zone  of  weathering.  Beneath  this 
lies  the  zone  of  enrichment,  underlaid  in  turn  by  the  zone  of 
primary  sulphides.  The  term  "  zone  "  is,  of  course,  only  used  for 
convenience,  since  it  is  well  known  that  weathering  extends 
down  along  fractures  and  other  channels  for  circulating  waters, 
sometimes  for  hundreds  of  feet  into  a  mass  of  otherwise  un- 
altered ore.  The  zone  of  enrichment  is  even  more  irregular, 
and  may,  as  illustrated  in  the  ideal  conditions  represented  in 

*  It  should  be  noted  that  the  word  oxidation  is  here  used  in  its  original  re- 
stricted sense,  as  it  is  commonly  understood,  and  not  in  the  extended  sense  used 
by  chemists  to  express  the  converse  of  reduction,  as,  for  instance,  Cu2S  to  CuS, 
where  no  oxygen  is  present. 


476  ENRICHMENT    OF    GOLD    AND    SILVER    VEINS. 

the  diagram,  Fig.  1,  be  separated  by  unaltered  ore  from  a 
bonanza  mass  of  secondary  ore  beneath. 

The  occurrence  of  enrichments  between  altered  and  un- 
altered vein-matter  is  one  that  has  not  escaped  the  attention  of 
previous  writers ;  but  they  have  all,  so  far  as  known  to  me, 
limited  such  enrichment  by  the  ground-water  level.  Thus, 
Penrose  says  :* 

"  As  a  result  of  these  various  changes,  certain  minerals  are  sometimes  leached 
from  the  upper  part  of  ore-deposits  which  have  become  porous  by  alteration  and 
carried  down  to  the  less  pervious  unaltered  parts.  Here  they  are  precipitated 
by  meeting  other  solutions  or  in  other  ways,  and  hence  the  richest  bodies  of  ore  in 
a  deposit  often  occur  between  the  overlying  altered  part  and  the  underlying  un- 
altered part.  This  is  not  always  the  case,  but  it  is  true  of  some  copper,  silver,  iron 
and  other  deposits." 

This  author,  it  is  true,  recognized  that  surface-waters  pass 
below  the  zone  of  oxidation  and  may  gradually  sink  to  very 
great  depths  below  the  permanent  water-level.  But  he  ex- 
pressly declares  that  the  results  of  such  circulation  do  not  re- 
late to  superficial  alteration, f  which  he  limits  to  that  of  deposits 
that  remain  in  situ.%  De  Launay,  in  his  very  interesting  and 
valuable  essay,  §  has  given  us  a  chemical  theory,  to  the  support 
of  which  he  has  marshaled  all  the  facts  gathered  in  the  prepa- 
ration of  his  great  monograph  on  ore-deposits.  This  author 
distinctly  recognizes  a  zone  of  enrichment,  but,  like  Penrose, 
limits  it  by  the  permanent  water-level  (niveau  hydrostatique). 

Leaching  in  the  Zone  of  Weathering. 

In  the  sulphide  enrichment  here  discussed,  the  enriched 
material  is  in  most  cases  derived  by  the  leaching  out  of  the 
metals  from  the  portion  of  the  vein  lying  above  ground-water 
level.  This  leaching  is  due  to  superficial  alteration,  and  leaves 
the  iron  as  a  gossan  while  the  waters  carrying  the  gold,  silver, 
copper  and  other  metals  in  solution  trickle  downward  through 
the  partially  altered  ores  into  cracks  and  water-courses  which 
penetrate  the  ore-body  below  the  water-level.  The  first  partof  the 
process  is,  therefore,  the  leaching  of  the  lean  ores  which  occurs 

*  Journ.  GeoL,  vol.  ii.,  1894,  p.  294. 
f  Loc.  tit,  p.  298. 
J  Loc.  tit.,  p.  302. 

3  "  Contribution  a  L' Etude  des  Gites  Me*tallif£res,"  Ann.  des  Mines,  9th  series, 
vol.  xii.,  1897,  pp.  119-227. 


ENRICHMENT    OP    GOLD    AND    SILVER    VEINS. 


477 


in  the  superficial  alteration  of  the  vein.  This  has  been  dis- 
cussed by  many  writers,  particularly  by  Penrose,  who,  however, 
does  not  make  any  attempt  to  state  the  chemical  reactions 
involved.  These  reactions  are  complex,  and  the  mass  results 
depend  upon  the  laws  of  physical  chemistry;  yet  the  general 


FIG.  1. 


Surface  of  ground 


Diagram  Showing  Kelative  Positions  of  Zones  of  Weathering,  Enrichment  and 
Unaltered  Ore,  and  of  Bonanzas  Formed  Along  Fault. 

changes  involved  may  be  expressed  by  equations  showing  end 
reactions. 

The  chemistry  of  weathering,  concisely  expressed,  is  as  fol- 
lows :  In  an  ore  consisting  of  either  one  or  all  of  the  following 
sulphides : — pyrite,  arsenopyrite,  chalcopyrite,  blende,  galena, 
tetrahedrite, — the  minerals  will  oxidize  according  to  their  rela- 
tive affinity  for  oxygen  and  inversely  as  their  "  affinity  "  for 
sulphur.*  All  the  sulphides  will  be  attacked  simultaneously, 

*  This  statement  is  sufficiently  accurate  for  the  purposes  of  this  discussion. 
As  the  mineral  decomposition  is  affected  by  physical  structure,  as  well  as  chemi- 
cal, and  by  relative  amounts  of  each  present,  it  is  apparent  that  there  are  many 
qualifying  factors.  The  ' '  relative  affinity  "  of  the  metals  for  sulphur  is  1  Hg,  2  Ag, 
3  Cu,  4  Sb,  5  Sn,  6  Pb,  7  Zn,  8  Ni,  9  Co,  10  Fe,  11  As,  12  Mn.  This  is  the  order 
in  which  a  salt  of  one  metal  will  be  decomposed  by  any  subsequent  one  in  the 
series  and  the  first  metal  precipitated  as  sulphide.  (See  E.  and  M.  Jour.,  Oct. 
25,  1890,  p.  484.  See  also  Jour,  of  Soc.  Chem.  2nd.,  vol.  xi.,  1892,  p.  869.) 


478  ENRICHMENT    OF    GOLD    AND    SILVER    VEINS. 

but,  inasmuch  as  pyrite  consists  of  4  parts  ferric  and  1  part 
ferrous  sulphide,*  and  parts  with  a  portion  of  its  sulphur  very 
readily,  this  mineral  will  be  most  attacked.  This  decomposes 
first  to  FeS  and  S.  The  sulphur  usually  forms  H2S04;  the 
FeS  forms  FeS04.  The  latter  changes  to  H2S04,  Fe(OH)3  and 
Fe2  (S04)3.  The  sulphuric  acid  attacks  more  iron  sulphide  and 
forms  more  FeS04  together  with  H2S — the  latter,  in  the  presence 
of  abundant  oxygen,  forming  H2S04.  The  FeSO4  changes  to 
Fe2(S04)3,  which  attacks  the  sulphides  of  copper,  lead,  zinc,  etc., 
in  a  reaction  which  can  be  most  simply  expressed  as  follows : 

Cu2S  +  5Fe2(S04)3  +  4H20  =  2CuS04  +  10FeS04  +  4H2S04. 

The  H2S04  in  mine-waters  will  attack  both  copper  and  iron 
sulphides  and  form  sulphates  without  the  formation  of  H2S  or 
the  liberation  of  free  S ;  and  the  iron  sulphate,  oxidizing  the 
iron,  is  precipitated  as  limonite.  The  oxygen  may  come  from 
either  air  or  water.  PbS  +  Fe2(S04)3  =  PbS04  +  2FeS04  +  S ; 
or  PbS  +  4Fe2(S04)3  +  4H20  =  PbS04  -f  8FeS04  +  4H2S04. 
And  ZnS  -f  Fe2(S04)3  =  ZnS04  +  2FeS04  +  S,  or,  more  prob- 
ably, ZnS  +  4Fe2(S04)3  +  4H20  =  ZnSO  4  +  8FeS04  +  4H2S04. 

The  -above  equations  simply  show  that  ferric  sulphate  can 
oxidize  the  various  sulphides  to  sulphates,  and  is  itself  reduced 
to  ferrous  sulphate.  However,  the  sulphuric  acid  formed  by 
the  oxidation  of  pyrite  in  the  upper  zone  can  also  attack  sul- 
phides, and  the  H2S  which  is  formed  may  be  oxidized  by  the 
ferric  hydrate  into  sulphuric  acid.  This  method  is  probably 
more  likely  of  occurrence,  but  no  one  can  say  that  the  oxida- 
tion is  exactly  according  to  any  set  of  equations,  as  many  other 
reactions  are  possible. 

The  laws  of  physical  chemistry,  verified  by  experiment,  show 
that  blende  is  more  easily  attacked  by  oxidizing  waters  than 
galena,  and  the  latter  mineral  decomposes  more  readily  than 
chalcocite.  The  general  order  of  attack  of  the  sulphides  is  there- 
fore arsenopyrite,  pyrite,  chalcopyrite  (FeS  removed,  leaving 
CuS),  blende,  galena,  chalcocite,  while  tetrahedrite,  being  a 
complex  substance  without  definite  percentage-composition,  has 
no  fixed  place.  Gold,  if  present,  may  be  attacked  by  Fe2(S04)3 
in  which  it  is  well  known  to  be  readily  soluble,  and  silver  goes 


*  "The  Chemical  Composition  of  Marcasite  and  Pyrite,"  by  Amos  P.  Brown, 
Proc.  Am.  Phil.  Soc.,  vol.  xxxiii.,  p.  225,  1894. 


ENRICHMENT    OF    GOLD    AND    SILVER    VEINS.  479 

into  solution  as  sulphate.  The  lead,  which  as  sulphate  is  nearly 
insoluble  and  remains  about  its  parent-mineral  galena,  can 
only  migrate  when  reduced  to  carbonate  (by  calcite,  etc.),  in 
which  condition  it  is  readily  carried  off  by  carbonated  waters. 

"Where  these  are  the  only  reactions,  the  outcrop  is  leached 
of  all  its  metallic  matter,  and  its  soluble  gangue-minerals  are 
reduced  to  a  porous  spongy  mass  of  silica,  such  as  is  sometimes 
seen.  Commonly  the  iron  is  not  all  removed,  since  the  ferrous 
sulphate,  which  is  the  most  abundant  product  of  the  leaching, 
absorbs  oxygen  and  water  and  forms  limonite,  2Fe2033H20 
(or  rarely  a  basic  sulphate  of  iron),  forming  the  iron-stained 
quartz  or  limonite  gossans,  the  "  iron  cap  "  of  so  many  vein 
outcrops.  This  leaching  of  the  ores  is  therefore  seen  to  depend 
upon  the  tendency  of  the  iron  salts  to  form  Fe(OH)3  as  an  ulti- 
mate product  which  is  precipitated  from  the  solution;  thus 
renewing  the  FeS04,  which  renews  the  ability  of  the  solution 
to  attack  more  pyrite  and  metallic  sulphides.  This  cycle  of 
change  can  be  tentatively  expressed  as  follows :  Ferric  sulphate 
forms  by  the  oxidation  of  the  iron  sulphide  of  the  original  ore. 
This  salt  attacks  pyrite  and  other  sulphides,  and  is  itself  re- 
duced to  ferrous  sulphate.  The  latter  oxidizes  to  ferric  sulphate, 
which  is  partly  changed  to  limonite  and  sulphuric  acid,  while 
the  remainder  begins  anew  the  cycle  of  change.  Ferric  sul- 
phate is  the  main  vehicle  by  w^hich  the  sulphides  are  dissolved. 
The  Fe(OH)3  is  in  part  eliminated  as  a  precipitate,  while  a  part 
is  acted  upon  by  the  sulphuric  acid  with  the  production  of  a 
solution  holding  Fe2(S04)3  +  FeS04,  these  iron  sulphates  being 
in  the  approximate  proportion  of  3 : 1.  The  FeS04  takes  up 
oxygen  and  forms  Fe(OH)3,  and  the  ultimate  production  is  a 
yellow  basic  sulphate  insoluble  in  H2S04.  The  result  of  these 
changes,  due  to  water  and  abundant  oxygen,  is  the  leaching  out 
of  all  the  constituents  of  the  vein  in  the  weathered  zone  except 
iron  and  silica.  The  solutions  seeping  downward  contain  vari- 
ous metallic  sulphates  and  much  sulphuric  acid,  the  amount  of 
the  latter  being  increased  by  that  formed  by  hydrolysis  from 
the  sulphates,  since  copper  sulphate  in  solution  yields  sulphuric 
acid. 

Precipitation  in  the  Zone  of  Weathering. 

Not  all  the  material  leached  out  in  the  zone  of  weathering 
migrates  below  to  the  zone  of  enrichment;  for  the  surface- 


480  ENRICHMENT   OF   GOLD   AND    SILVER   VEINS. 

waters  commonly  contain  carbon  dioxide,  some  chlorides, 
organic  matter,  etc.,  resulting  in  the  formation  of  carbonates, 
chlorides,  etc.,  and  of  the  native  metals.  Thus,  copper  can  be 
formed  from  the  oxide  by  reaction  with  either  free  sulphuric 
acid  or  iron  sulphate  (both  abundant  in  the  lower  part  of  the 
superficial  zone),  viz. :  Cu20  +  H2S04  =  Cu  +  CuSO,  +  H20 ;  and 
3Cu20  +  6FeS04  =  6Cu  +  Fe203  +  2Fe2(S04)3.  The  latter  reac- 
tion accounts  for  the  cement-copper  associated  with  iron  sesqui- 
oxide  at  Ducktown,  Tenn.,  Gold  Hill,  !N~.  C.,  and  elsewhere. 
Native  silver  is  also  formed  in  films  and  crystalline  masses  by 
reduction  through  ferrous  sulphate,  viz. :  Ag2S04  +  2FeS04  = 
2  Ag  +  Fe2(S04)3.  Gold  probably  sometimes  occurs  in  the  native 
state  because  it  has  not  been  attacked  and  is  simply  left  behind, 
though  it  is  also  deposited  by  precipitation  from  the  ferrous 
sulphate  solution. 

The  Zone  of  Enrichment. 

The  surface-waters  which  have  leached  the  vein  in  the  zone 
of  weathering  seep  downward  along  cracks  and  crevices,  or 
along  trunk-channels,  into  the  primary  ore  below.  The  origin 
and  occurrence  of  such  fractures  will  be  mentioned  later. 
They  very  commonly  exist  in  ore-deposits,  and  convey  waters 
downward  far  below  the  so-called  ground-water  level.  As  we 
have  shown,  these  waters  not  only  carry  various  metals  in  solu- 
tion, chiefly  as  sulphates,  but  they  are  no  longer  oxidizing,  but 
are  of  acid  reaction.  Penetrating  the  primary  ore,  they  come 
in  contact  with  the  unaltered  metallic  sulphides.  In  such 
masses  pyrite  and,  more  rarely,  pyrrhotite  are  very  commonly 
abundant;  and  a  reaction  at  once  occurs  between  the  iron  sul- 
phide and  the  metallic  salts  (mainly  sulphates)  held  in  solution, 
resulting  in  their  decomposition  and  the  precipitation  of  new 
sulphides  which  encrust  the  walls  of  the  fractures.  This,  in 
the  case  of  copper,  is  shown  by  the  following  theoretical  equa- 
tion, which  expresses  end  reactions  only,  viz. :  4CuSO±-f-3FeS2 
+  4H20  =  2Cu2S  +  3FeS04  +  2H2S04  +  2H£  +  S ;  or,  more 
simply,  copper  sulphate  and  pyrite  yield  copper  sulphide  and 
ferrous  sulphate.*  This  Cu2S  would  react  in  turn  upon  silver 
sulphate,  Ag2S04  +  CuaS  =  Ag2S  +  Cu2S04,  while  the  pyrite 

*  The  apparent  anomaly  of  cupric  sulphate  and  pyrite  giving  ferrous  sulphate 
is  explained  by  the  chemical  composition  of  pyrite  as  4  parts  ferric  sulphide  and 


ENRICHMENT    OF    GOLD    AND    SILVER    VEINS.  481 

itself  will  decompose  the  silver  as  well  as  other  sulphates, 
owing  to  the  relative  affinity  of  the  metals  for  sulphur.  Chlo- 
ride or  carbonate  of  silver  would  be  similarly  decomposed. 
For  the  rich  antimonial  sulphides  of  silver  various  reactions  are 
possible,  the  pyritous  ore  reducing  the  minerals  from  a  solution 
holding  antimony  and  arsenic  derived  from  impure  pyrite.  This 
process  is  probably  aided  by  the  free  sulphuric  acid  brought 
down  in  the  waters  and  as  hydrolization-product  of  intermedi- 
ate steps  of  above  reactions;  since  a  dilute  solution  of  sul- 
phuric acid  attacks  iron  sulphide,  forming  iron  sulphate  and 
sulphuretted  hydrogen,  the  latter  of  which  would  form  sul- 
phides of  lead  or  silver,  etc.,  from  the  solutions.* 

For  lead  the  presence  of  carbonates  seems  necessary,  and  if 
the  gangue  minerals  are  of  this  nature,  or  the  walls  are  lime- 
stone, the  lead  carbonate  is  decomposed,  lime  goes  into  solu- 
tion, and  the  H2S  set  free  from  pyrite  at  once  forms  galena, 
which  is  deposited. 

The  Solution  and  Precipitation  of  Gold. — The  alteration  of 
gold-deposits  presents  features  differing  very  markedly  from 
those  accompanying  the  alteration  of  copper-  or  silver-ores.  It 
is  commonly  assumed  that  the  unaltered  ore  contains  the  gold 
in  association  with  pyrite  or  quartz.  The  most  frequent  altera- 
tion of  this  is  to  a  rusty  brown  mass  of  sesquioxide  of  iron, 
permeating  the  quartz  and  holding  nugget-threads  of  free  gold. 
As  a  result  of  further  alteration  by  surface-waters,  the  iron  is 
leached  out,  and  a  porous,  spongy,  white  quartz  remains,  holding 
the  gold.  This  kind  of  alteration  is  a  very  common  feature  of 
ore-deposits  throughout  the  West.  In  many  cases,  however, 
different  conditions  prevail.  Part  of  the  gold,  at  least,  is  taken 
into  solution  by  ferric  sulphate,  carried  downward  as  the  waters 

1  part  ferrous  sulphide,  the  latter  only  being  herein  considered.  Moreover,  we 
may  have  in  oxidation  zone:  Cu23  +  4Fe2(SO4)8  +  4HaO  =  Cu2SO4  +  8FeSO4 
-j-4H2S04.  Then  any  sulphide  would  precipitate  Cu2S  from  the  cuprous  sul- 
phate, providing  the  sulphide  is  soluble  enough  and  the  sulphate  solution  is 
strong  enough  to  have  enough  cuprous  ions  and  sulphide  ions  to  exceed  the  con- 
stant of  solubility.  The  formation  of  cuprous  sulphate  is  theoretical,  but  its 
existence  is  indicated  by  recent  experimental  work,  as  yet  unpublished,  by  C.  F. 
Tolman,  Jr. 

*  It  must  be  understood  that  these  equations  are  given  in  the  simplest  and 
most  compact  form  possible.  Thus  CuSO4  in  water  really  holds  Cu(OH)2  and 
H2S04. 


482 


ENRICHMENT    OF    GOLD    AND    SILVER    VEINS. 


seep  below,  and  precipitated  as  native,  leaf,  wire  or  scale  gold 
in  minute  cracks  in  sulphide  ores,  or,  what  is  more  commonly 
the  case,  the  gold  is  deposited  with  silver  in  antimonial  sul- 
phides, especially  ruby  silver  (pyrargyrite).  This  is  the  form 
in  which  it  occurred  at  the  Ruby  mine,  on  Lowland  creek  (near 
Butte),  where  the  surface  of  the  quartz  crystals  lining  the  open 
spaces  between  boulders  of  decomposed  rhyolite  and  coating 
these  boulders  is  liberally  sprinkled  with  ruby  silver.  This 
mine  yielded  $600,000  in  less  than  a  year,  of  which  one-half 
the  value  was  gold.  The  ore  was  a  secondary  concentration 
along  a  clay  fault-fissure,  and  is  now  exhausted.  The  "in- 
dicators "  of  Australian  ore-deposits  afford  a  most  interesting 

FIG.  2. 


Alteration  of  Bornite  to  Chalcocite  and  Limonite,  Blue  Wing  Ore,  Virgilina 
District,  N.  C.  The  nucleal  masses  are  bornite  ;  the  black  borders  represent 
chalcopyrite  ;  the  stippled  area  is  iron  oxide.  Drawn  from  nature,  twice  the 
natural  size. 

example  of  the  reduction  of  gold  by  pyrite.  These  indicators 
are  thin  layers,  sometimes  but  half  an  inch  thick,  of  pyrite 
occurring  in  shale.  In  many  cases  the  shales  are,  it  is  true, 
carbonaceous,  and  the  organic  matter  may  assist  in  the  reduc- 
tion. As  shown  by  Don  and  by  Rickard,  the  quartz  veins  are 
barren  except  where  they  intersect  these  pyritous  layers.  * 

The  experiments  of  Liversidgef  have  shown  that  gold  is 
precipitated  from  solution  more  readily  by  metallic  sulphides 
than  by  organic  matter. 

*  J.  E.  Don,  Trans.,  xxvii.,  p.  569.  T.  A.  Eickard,  E.  and  M.  Jour.,  189$, 
lx.,  p.  561. 

f  Proc.  Rvy.  Soc.  N.  S.  W.,  vol.  xxvii.,  1893,  p.  287.  See  precipitation  of  gold 
by  pyrite  in  the  experiments  of  Daintree,  quoted  by  Eickard  in  "Origin  of  the 
Gold-Bearing  Quartz  of  Bendigo  Eeefs,"  Trans.,  vol.  xxii.,  p.  313. 


ENRICHMENT    OF    GOLD    AND    SILVER    VEINS. 


483 


Resume. — It  seems  unnecessary  to  expand  this  section  further, 
as  the  reactions  given  are  sufficient  to  show  that  secondary 
sulphides  are  formed  in  depth.  It  is  evident  that  a  majority 
of  the  reactions  depend  upon  the  presence  of  iron  sulphides, 
either  as  pyrite  or  in  some  other  form.  Pyrite  is  therefore  the 
great  precipitant  of  secondary  sulphides. 

EVIDENCE  THAT  CERTAIN  MINERALS  AND  ORES  HAVE  THE 
GENESIS  STATED  ABOVE. 

That  chemical  reactions  similar  to  those  given  do  take  place 
in  nature,  and  that  the  resulting  precipitates  are  true  minerals, 
is  shown  by  abundant  mineralogical  proof.  Thus  the  aurifer- 
ous copper-ores  of  Gold  Hill,  North  Carolina,  show  chalcopyrite 


FIG.  3. 


Barite  tablets  with  parasitic 
galena,  leached  of  lead,  leaving 
polybasite  (pearcite)  sponge. 

Galena,  blende 


Pyrjte,  barite 


Specimen  Showing  Leached  Galena  and  Residual  Polybasite ;  Florence  Mine, 

Neihart,  Montana. 

altering  about  its  borders  to  a  spongy  mass  of  black  copper 
sulphide ;  the  iron  being  largely  carried  off,  but  in  part  form- 
ing hematite  nests  near  by.  In  other  specimens,  the  copper 
sulphide  has  gone  into  solution,  and  has  been  carried  a  few 
inches  and  redeposited  in  crystalline  masses.  In  a  similar 
manner  bornite  alters  to  chalcocite  and  iron  oxide,  as  shown  in 
specimens  from  the  Blue  Wing  mine  at  Yirgilina,  Person 
county,  North  Carolina.  Fig.  2,  drawn  from  nature,  shows 
this  alteration.  In  other  specimens  the  iron  is  carried  off  and 
fills  cavities  with  specular  iron-ore. 

At  Neihart,  Montana,  polybasite  and  pyrargyrite   encrust 
barite,  quartz,  galena  and  pyrite,  which  are  themselves  later 

31 


484  ENRICHMENT    OF    GOLD    AND    SILVER    VEINS. 

than  and  encrust  fractured  masses  of  impure  galena,  blende 
and  pyrite  that  constitute  the.  original  vein-filling.  •  These  crusts 
are  now  forming  in  vugs  and  water-courses  filled  by  sluggish 
descending  water.  Nucleal  masses  of  impure  galena  are  seen 
in  thin  section  surrounded  by  a  spongy  mass  of  polybasite,  just 
as  chalcopyrite  is  seen  surrounded  by  amorphous  copper  glance. 
Fig.  3  is  a  diagrammatic  representation  of  a  portion  of  the 
surface  of  a  specimen  of  ore  from  the  Florence  mine.  The 
main  mass  of  the  specimen  consists  of  a  breccia  of  pyrite  frag- 
ments, held  in  a  cement  of  barite  and  ankerite  spar,  with 
scattered  grains  of  galena.  The  upper  surface  shows  galena, 
blende  and  barite,  the  latter  in  projecting  tablet-shaped  crystals 
upon  which  there  are  parasitic  masses  of  impure  argentiferous 
galena.  This  galena  is  etched  and  leached  so  that,  on  part  of 
the  specimen,  the  surface  shows  a  crust  of  about  T^  to  J  inch 
thickness  consisting  of  a  spongy  residue,  or  a  skeleton  of  the 
galena.  This  spongy  mass  consists  largely  of  polybasite  left 
behind  as  the  more  soluble  lead  was  leached  out.  That  some 
of  the  antimonial  sulphide  of  silver  goes  into  solution,  is  shown 
by  the  presence  nearby  of  minute  newly-formed  crystals  of  the 
latter.  The  crystalline  polybasite  occurs  nearby  coating  frac- 
tures and  showing  characteristic  triangular  markings,  or  as 
loose  aggregates  of  rough  and  mossy-surfaced  crystals.  It  is 
also  probably  derived  from  blende,  as  it  occurs  very  commonly 
coating  that  mineral  under  conditions  which  seem  to  preclude 
precipitation  by  that  mineral.  An  examination  of  numerous 
specimens  from  the  Florence  and  Big  Seven  mines  shows  that 
polybasite  and  pyrargyrite  are  secondary  minerals  filling  cavi- 
ties and  cracks  in  the  original  ore.  The  material  gathered  from 
the  lowest  level  of  the  Florence  mines  shows  polybasite  in  the 
form  of  crystalline  tablets  upon  barite  and  other  minerals,  and 
also  as  a  moss-like  mass  of  open  skeleton-texture,  which  seems 
to  represent  arrested  deposition.  The  latter  form  is  believed  to 
come  from  a  place  in  the  vein  where  mineral-bearing  water  is 
now  depositing  this  mineral,  together  with  spar,  quartz,  and 
probably  galena.  Studied  under  the  microscope,  the  polybasite 
appears  to  be  an  alteration-product  of  galena,  and  itself  to  be 
mixed  with,  and  to  grade  into,  pyrargyrite,  which  is  in  some 
cases  its  undoubted  alteration-product.  It  is  certain  that  poly- 
basite, as  the  important  constituent  of  many  of  the  ores,  is  of 


ENRICHMENT    OF    GOLD    AND    SILVER    VEINS.  485 

secondary  origin.  It  occurs  on  all  other  minerals,  and  is  itself 
not  coated  or  dotted  by  them.  Fig.  4  is  a  diagram  of  a  speci- 
men of  the  common  ore  of  the  district  consisting  of  galena 
and  carbonate  "  spar  "  with  scattered  pyrite  and  chalcopyrite. 
The  specimen  is  from  the  wall  of  a  fracture  traversing  the 
somewhat  friable  bands  of  galena.  The  surface  of  the  fracture 
has  been  coated  with  a  thin  drusy  covering  of  quartz  upon 
which  there  rests  massive  polybasite  whose  upper  surface 
shows  the  typical  triangle  striations  of  polybasite.  The  speci- 
men is  drawn  nearly  to  natural  scale. 

Sphalerite  also  occurs  in  well-formed  crystals  in  some  of  the 
vugs  arid  is  one  of  the  most  recently  deposited  minerals. 

FIG.  4. 

Secondary  "triangle"  ore; 
polybasite  encrusting  frac- 
tured surface  of  primary  ore. 

_Primary  ore;  galena  and 
"carbonate  minerals:  no 
quartz,  some  pyrite  and 
chalcopyrite. 

Specimen  from  the  Florence  Mine,  Neihart,  Montana. 

While  polybasite  and  pyrargyrite  are  economically  the  most 
important  of  the  secondary  minerals  formed  by  enrichment- 
fractures  in  the  Neihart  ore,  yet  other  minerals,  galena,  pyrite, 
blende  and  quartz,  are  also  formed.  An  excellent  example  is 
seen  where  quartz  veinlets  have  filled  fractures  in  the  primary 
ore.  Fig.  5  shows  a  piece  of  the  common  spar  and  galena  ore 
in  which  the  ore  is  fractured  and  the  fissure  filled  by  a  veinlet 
of  quartz  in  whose  center  pyrite  is  seen.  At  the  top  the  fissure 
is  open  and  the  vug  is  lined  with  a  drusy  coating  of  quartz,  on 
the  surface  of  which  occasional  larger  crystals  of  polybasite 
are  seen.  The  druse  (c),  connected  with  the  quartz  veinlet  by 
a  fracture  following  a  layer  of  spar,  shows  secondary  quartz 
and  pyrargyrite.  Where  such  fractures  traverse  the  ore,  and 
its  carbonate  gangue  is  at  a  decided  angle  to  the  banding  of 
the  deposit,  and  the  crusts  or  filling  are  notably  different  in 
composition,  there  is  no  doubt  of  their  being  of  later  origin. 
A  veinlet  of  this  kind  is  illustrated  on  a  natural  scale  in  the 
diagram,  Fig.  6.  In  this  case  various  secondary  minerals  were 
formed.  The  figure  represents  a  cross-section  of  a  little  quartz 


486  ENRICHMENT    OF    GOLD    AND    SILVER    VEINS. 

"  vein "  of  the  Big  Seven  mine,  which  constitutes  the  high- 
grade  ore-streak  of  the  lode.  It  shows  the  relative  abundance 
and  association  of  the  minerals,  but  does  not  represent  the 
spongy  texture  of  the  polybasite  and  its  intimate  admixture 
with  both  galena  and  pyrites  (chalcopyrite),  as  this  growth  is 
too  mossy  to  be  represented  well,  and  the  mineral  is  therefore 
indicated  as  polybasite  alone.  The  specimen,  seen  in  thin  sec- 
tion, shows  ruby  silver  and  polybasite  intimately  associated 
and  forming  irregular,  shreddy  and  ragged  patches.  No  posi- 
tive identification  of  galena  as  the  nucleus  of  such  masses  was 
made,  but  the  association  with  galena  is  such  as  to  indicate  a 
possible  change  to  polybasite.  The  pyrite  is  broken  and  frac- 

FIG.  5. 


=  Druse  forming  part  of  secondary 
quartz  veinlet  -  quartz  encrusted 
with  pyrite  and  polybasite. 

=  Secondary  quartz  veinlet  with 
pyrite  center. 


C  =  Vug  in  galena  and  carbonate  ore. 
shows  secondary  leaching  and  de- 
position of  quartz  in  cavity. 

b 
Specimen  of  Silver-  and  Lead-Ore  from  Neihart,  Montana. 

tured,  but  the  grains  are  always  sharply  defined,  and  no  genetic 
relation  to  the  silver  sulphides  is  recognizable.  A  blende 
crystal,  seen  isolated  in  the  central  quartz-filling,  shows  in  thin 
section  a  crust  of  polybasite,  the  latter  holding  minute  inclu- 
sions of  pyrite.  The  blende,  seen  in  another  section  of  rich  ore, 
is  invariably  surrounded  by  a  dark  crust  which  is  not  iron  oxide, 
nor  does  it  appear  to  be  an  iron-rich  blende.  It  is  not  definitely 
determinable,  but  resembles  galena  or  a  silver  sulphide. 

Posepny  has  described  stalactitic  deposits  of  sulphide,  which, 
as  urged  by  Dr.  A.  Schmidt,*  form  excellent  proof  of  the 
formation  of  secondary  sulphides  by  a  leaching  of  ore  in  the 
zone  of  weathering  and  a  redeposition  of  ore  in  the  zone  of 
enrichment.  Posepny,  it  is  true,  denied  such  an  origin  for 
these  deposits  because  they  occurred  below  water-level.  The 

*  Die  Zinkerzlagerstatten  von  Wiesloch,  in  Baden,  Heidelberg,  1881,  p.  94. 
Posepny,  Genesis  of  Ore  Deposits,  p.  63  ;  and  Trans.,  xxiii.,  259. 


ENRICHMENT    OF    GOLD    AND    SILVER    VEINS.  487 

existence  of  open  spaces  below  water-level  is  a  phenomenon 
frequently  encountered  in  ore-bodies  exposed  by  mine-work- 
ings. I  myself  have  seen  such  openings  a  foot  or  more  across 
at  1000  feet  below  the  water-level  at  Elkhorn,  Montana,  and  at 
200  feet  below  water-level  at  Neihart.  The  pipe-ore  of  Raibl 
described  by  Posepny  is,  I  believe,  an  excellent  example  of  the 
formation  of  secondary  minerals  by  descending  waters.  Posep- 
ny's  explanation  that  they  are  due  to  ascending  waters  which 
were  denied  access  to  the  cavity  except  through  the  roof, 
seems  to  me  to  be  an  hypothesis  opposed  to  both  the  facts  of 
observation  and  physical  laws.  Moreover,  as  the  geology  of 
the  mining  regions  is  more  carefully  studied,  it  is  certain  that 
they  have  passed  through  various  physiographic  changes,  with 
migration  of  water-level,  so  that  air-filled  spaces  below  what 
is  now  the  water-level  are  not  only  possible  but  in  some  cases 
probable.* 

Prof.  Yogt  also  describesf  the  recent  concentration  of  gold 
and  silver  in  a  zone  beneath  the  "  iron  hat."  He  says  that  in 
the  Rio  Tinto  region  the  "  iron  hat "  is  from  35  to  50  meters 
deep,  and  consists  of  iron  oxide  or  hydrated  oxide,  with  from 
35  to  50  per  cent,  of  iron,  some  silver  in  part  as  basic  sulphate, 
and  a  few  ten-thousandths  per  cent,  of  arsenic,  while  on  the 
other  hand  the  copper-contents  are,  as  already  remarked,  en- 
tirely oxidized  and  dissolved  out.  In  one  mine,  North  vein 
~No.  2,  at  Rio  Tinto,  there  occurred  between  the  iron  hat  and 
the  underlying  comparatively  fresh  pyrite,  a  layer  of  earthy, 
porous  material,  bearing  gold  and  silver.  This  earthy  ore, 
though  a  few  decimeters  in  thickness,  may  be  followed  con- 
tinuously over  the  entire  ore  body.  This  very  marked  layer 
follows  closely  the  irregular  plane  between  the  iron  hat  and 
the  underlying  pyrite.  It  everywhere  contains  an  average 
gold-  and  silver-contents  of  from  15  to  30  grammes  gold  and 
1.025  silver,  with  a  value  of  about  150  marks  per  ton.  In 
stripping  off  the  "  iron  hat,"  this  earthy  mass  is  carefully  laid 
to  one  side,  and  has  thus  yielded  fully  a  thousand  tons  of  ore. 
It  is  clear  that  the  formation  of  this  gold-  and  silver-bearing 
zone  is  connected  with  the  oxidizing  process  that  formed  the 
iron  hat,  and  that  the  gold  and  silver  comes  from  the  very 
small  percentage  of  such  metals  in  the  primary  ore. 

*  This  volume,  p.  69;  and  Trans.,  xxiii.,  260.  f  Zeitsch.  Prak.  OeoL,  July,  1899. 


488  ENKICHMENT    OF    GOLD    AND    SILVEK    VEINS. 

Deductions. 

From  the  chemical  reactions  given,  it  is  evident  that  enrich- 
ment is  largely  dependent  upon  the  presence  of  marcasite, 
pyrite  or  some  other  form  of  iron  sulphide  in  the  primary  ore, 
since  lixiviation  depends  upon  the  presence  of  the  iron  sul- 
phates, and  precipitation  is  mainly  effected  by  the  unaltered 
sulphides.  As  a  consequence  of  this,  it  follows  that  ore-bodies 
lacking  in  iron  pyrites  will  not  show  enrichment,  thus  explain- 
ing the  absence  of  any  such  phenomena  in  the  pure  silver-lead 
bodies  of  the  Co3ur  d'Alene  district  and  elsewhere.  In  this 
region,  visited  by  the  writer  in  1895,  the  ore-bodies  consist  of 
galena  with  a  siderite  gangue  and  are  replacement-deposits  in 
quartzite  and  argillaceous  schists.  The  veins  are  covered  by 
great  masses  of  barren  limonite  gossan,  beneath  which  the  ores 
are  carbonates  and  sulphates  of  lead,  which  extend  along  frac- 
tures to  a  depth  of  200-300  feet.  The  silver  values,  which 
carry  about  10  ounces  of  silver  to  1  per  cent,  of  lead,  do  not 
show  any  enrichment.  This  is  quite  what  would  be  expected, 
since,  although  the  galena  in  decomposing  would  yield  up 
silver  as  sulphate,  there  would  be  no  reducing  agent  at  hand 
to  extract  it  from  the  waters  as  it  seeped  down  into  the  un- 
altered ore.  Also,  at  Barker,  Montana,  the  ore-bodies  show 
no  enrichment,  though  a  common  feature  of  such  deposits, 
viz.,  the  change  of  galena  to  pyrite,  in  depth,  would  favor 
enrichment,  if  the  silver-lead  bodies  were  deeply  enough 
weathered.  The  writer  has  also  examined  the  Zosel  mines  in 
andesite  porphyry  near  Deer  Lodge,  Montana,  and  those  in 
similar  rocks  on  Basin  Creek,  and  near  Elliston,  as  well  as  the 
Castle  Mountain  and  Elkhorn  ores  in  limestone,  and  the  Bear 
Paw  ores  in  basalt,  all  in  Montana,  as  well  as  the  McMakin  in 
North  Carolina.  These  deposits  all  consist  essentially  of  galena 
without  any  notable  amount  of  pyrite,  and  although  favorable 
physical  conditions  for  enrichment  occur,  no  bonanzas  or  pay- 
streaks  of  rich  secondary  ores  are  found. 

The  Occurrence  of  Bonanzas  and  Pay-Streaks. 
The  location  of  bonanzas  and  pay-streaks  of  secondary  sul- 
phide-ores is  dependant  upon  physical  factors.     From  a  con- 
sideration of  the  processes  described  in  the  preceding  pages, 
it  is  evident  that  the  localization  of  enrichments  will  depend 


ENKICHMENT    OF    GOLD    AND    SILVER    VEINS. 


489 


wholly  upon  structural  conditions.  If  the  vein  consists  of  a 
solid  unshattered  impermeable  body,  with  no  fractures  by  which 
the  solutions  can  seep  down  into  the  underlying  original  sul- 
phides, the  zone  of  enrichment  will  be  confined  to  the  vicinity 
of  the  water-lines,  and,  if  above  water-level,  will  constitute  the 
ore-bodies  described  by  Penrose,  De  Launay  and  others  as  one 
of  the  results  of  superficial  alterations.  In  fact,  many  such  en- 
richments do  occur  at,  or  just  below,  the  water-level.  If  the 
primary  ore-body  is  shattered  by  cracks,  sheeted  by  later  move- 
ment or  traversed  by  secondary  fractures,  faults  running  with 


FIG. 


Polybasite<&  Pyrargyrite) 


Galena 


Pyrite 


— . Blende 


=-  > '. —   Quartz-fibrous 


Quartz 


Secondary  Veinlet  of  Quartz  and  Rich  Sulphide  Ore  Filling  Fracture  in  Pri- 
mary Ore  :  Big  Seven  Mine,  Neihart,  Montana.  Pyrite  and  galena  are  angular 
fragments  of  original  ore. 

or  across  the  vein,  such  crevices  and  fractures  will  be  the  chan- 
nels in  which  the  descending  solutions  will  travel,  and  along 
which  the  secondary  ores  will  form  deposits  in  the  unaltered 
ore  below. 

Such  secondary  fractures  may  be  now  filled  with  quartz  or 
other  gangue-minerals  holding  ore,  or  they  may  be  barren  and 
open,  or  they  may  be  marked  by  a  soft  mushy  mass  of  clay  or 
attrition  breccia.  Very  often  the  so-called  splits,  feeders  and 
stringers  of  a  vein,  when  examined  critically,  will  be  found  to 
be  secondary  fractures  and  not  true  offshoots  of  the  vein  itself, 
the  latter  phenomenon  often  being  the  cause  of  ore-shoots  of 
primary  origin.  "Where  the  later  fracturing  runs  parallel  to 


490 


ENKICHMENT    OF   GOLD   AND    SILVER   VEINS. 


the  vein,  as  is  so  often  the  case  at  Butte,  and  in  the  silver  mines 
of  Jefferson  county,  it  may  only  be  revealed  by  a  clay  selvage 
of  a  rare  slickenside  surface,  though  it  is  more  frequently 
marked  by  a  soft  and  mushy  mass  of  mud  and  breccia,  in 
which  fragments  of  the  wall-rock  ore  and  gangue,  one  or  all, 
may  be  seen.  This  is  seen  at  the  Comet  mine,  where  second- 
ary ores  were  abundant  along  recent  fissures  filled  with  clay 
and  a  breccia  of  leached  ore  and  altered  wall-rock. 

An  excellent  example  is  afforded  by  the  ore-body  of  the 
Australian  Broken  Hill  Consols  mine,  New  South  "Wales,  de- 
scribed by  Smith.*  The  occurrence  of  the  largest  bonanzas  yet 

FIG.  7. 


CROSS-SECTION   OF   RICH   ORE-BODY, 
LOOKING    NORTH-EAST. 

P         1         ?         8         4Ft. 
Approx:  scale 


Australian  Broken  Hill  Consols  Mine,  New  South  Wales.      (After  George  Smith, 

Trans.,  xxvi.,  73.) 

A,  dyscrasite ;  B,  stromeyerite ;  C,  decomposed  amphibolite,  etc. ,  assaying 
under  7  oz.  per  ton  ;  D,  fahlerz  ;  E,  soft  gossany  material,  containing  nodules  of 
silver  chloride,  stromeyerite,  etc.,  and  averaging  about  750  ozs.  per  ton;  F, 
limonite,  practically  free  from  silver  ;  G,  cross-vein  ;  H,  amphibolite. 

found  in  the  mine  were  in  association  with  the  vertical  vein  G, 
shown  in  the  diagram  (Fig.  7).  This  cross-vein  has  been  faulted 
by  the  lode,  and  is  really  a  succession  of  joints  along  a  line  of 


*  Trans.,  xxvi.,  69. 


ENKICHMENT    OF    GOLD    AND    SILVER    VEINS.  491 

weakness.  Another  bonanza  occurs  in  the  same  mine,  500 
feet  to  the  east,  under  similar  conditions. 

Mr.  Smith's  statement  is  that  the  lode  itself  is  only  ore-bear- 
ing where  it  makes  junction  with  cross-veins.  The  well-known 
occurrence  in  Australia  of  ore-bodies  where  veins  cross  "  in- 
dicators," i.e.,  pyritic  bands  a  few  inches  wide,  is  readily  under- 
stood, either  as  secondary  enrichment  or  primary,  since  the 
reducing  effect  of  pyrite  upon  gold  held  in  solution  has  been 
established  by  Liversidge. 

The  part  played  by  such  secondary  fractures  at  Butte  can 
hardly  be  appreciated  by  those  not  familiar  with  the  ground. 
In  descriptions  and  diagrams  of  the  veins  of  this  district  the 
occurrence  of  clay  and  breccia  bands  and  walls  has  not  been 

FIG.  8. 


Diagram  to  Show  Kelation  of  Mollie  Gibson  and  Smuggler  Ore-Bodies  and  Bonan- 
zas (of  Polybasite)  to  Fault-Fissures.     (From  Spurr. ) 

overlooked,  though  their  true  significance  appears  to  have  es- 
caped notice  since  the  fractures  so  often  run  parallel  with  and 
in  the  vein  itself.  Emmons  first  noted  the  significance  of  such 
fractures,  and  their  genetic  connection  with  glance  and  bornite 
veins.  It  is  now  known  that  these  fractures  are  extensive 
laterally  and  vertically,  and  the  enrichment  probably  due  to 
them  extends  in  some  instances  to  a  depth  of  2000  feet  below 
the  present  surface.  Lest  this  statement  prove  misleading,  it 
should  be  qualified  by  adding  that  not  all  such  fractures  have 
caused  enrichment,  and  some  of  the  largest  fault-fractures  are 
of  relatively  recent  formation,  later  than  the  ore-bodies  of 
glance  and  bornite,  etc.,  which  they  cross. 

In  his  monograph  upon  the  Aspen  district,  Colorado,*  Mr. 

*  J.  E.  Spurr,  U.  S.  Geol.  Survey,  Monograph  No.  xxxi.,  Geology  of  the  Aspen 
Mining  District. 


492  ENRICHMENT    OF    GOLD   AND    SILVER   VEINS. 

Spurr  describes  the  occurrence  of  the  famous  ore-bodies  of  the 
Smuggler  and  Mollie  Gibson  mines  at  Aspen,  Colorado.  The 
ore  consists  of  barite  and  polybasite,  with  tennantite.  Although 
Mr.  Spurr  gives  no  definite  statements  as  to  the  possible  sec- 
ondary origin  of  these  ores,  yet  the  sketch  which  he  gives*  (Fig. 
8)  and  the  descriptions  all  indicate  that  the  original  ore  was  a 
silver-bearing  lead  sulphide,  with  more  or  less  iron  and  zinc 
sulphides,  formed  along  inclined  faults,  and  that  subsequent  to 
the  formation  of  these  ore-bodies,  nearly  vertical  faults  dis- 
placed the  ore  and  formed  the  two  bodies  now  worked  at  the 
mines  mentioned.  Although  in  these  vertical  or  nearly  verti- 
cal fissures  rich  polybasite  ore  is  now  found,  it  does  not  extend 
far  in  either  direction  from  this  fault ;  and  the  description  of 
the  ores  given  by  Mr.  Spurr  indicates  that  it  is  derived  by  sec- 
ondary alteration-processes  from  the  lead  and  zinc  ore-bodies. 
This  is  also  indicated  by  the  fact  that  the  polybasite  is  in^part 
altered  to  native  silver  at  the  extreme  lower  end  of  the  ore- 
body. 

In  conversation  with  me,  Mr.  Spurr  has  admitted  the  possi- 
ble secondary  origin  of  these  polybasite  bodies,  but  had  no  new 
evidence  upon  the  subject.  He  says: 

"This  ore  was  of  a  rich  character,  having  large  amounts  of  polybasite  and 
native  silver.  Thist polybasite  body  appears  to  lie  in  a  sort  of  subordinate  shoot, 
trending  south  of  east  and  lying  at  the  Gibson  fault-plane.  This  shoot  is  marked 
by  exceptionally  large  and  rich  bodies  of  a  nature  not  found  elsewhere  in  the 
mine.  It  is  noteworthy  that  this  rich  shoot  is  practically  the  lower  termination 
of  the  ore  of  the  Gibson  fault.  Most  of  the  ore  below  this  is  native  silver,  which, 
from  the  nature  of  its  occurrence,  is  manifestly  a  secondary  deposit  leached  from 
the  rich  ore  above.  Some  of  these  secondary  deposits  are,  however,  of  consider- 
able size,  and  empty  vugs  are  often  found  beautifully  and  elaborately  festooned 
with  delicate  wires  of  silver.  Above  the  polybasite  ore,  however,  the  ore  appears 
to  be  pretty  continuous,  but  the  amount  of  silver  becomes  less." 

It  will  be  noticed  that  he  recognizes  the  secondary  nature  of 
the  silver,  and  that  the  polybasite  lies  between  the  native  silver 
and  the  lead  sulphide. 

In  a  chapter  upon  the  chemical  geology  of  the  region,  where 
he  discusses  the  alteration  of  the  ore-deposits  and  of  the  lime- 
stones, he  does  not  adduce  any  new  facts  concerning  the  forma- 
tion of  the  polybasite  ore ;  but  he  does  say  that  iron  pyrites 
carrying  small  amounts  of  arsenic,  lead,  copper,  zinc,  cadmium, 

*  Op.  C&,  183. 


ENRICHMENT   OP   GOLD   AND    SILVER   VEINS.  493 

cobalt  and  nickel  is  found,  and  that  tetrahedrite  is  also  very 
common.     The  polybasite  is  said  to  be  later  than  the  barite. 

The  description  given  by  Leggett*  of  the  Rosario  mine,  San 
Juancito,  Honduras,  C.  A.,  shows  that  the  secondary  enrich- 
ment may  account  for  the  peculiar  features  of  the  deposit. 
This  fissure-vein  splits  into  two  distinct  veins  in  more  barren 
ground  and  unites  into  one  consolidated  vein  where  ore-bodies 
occur  and  where  feeders  enter  from  the  hanging-wall — a  con- 
dition paralleled  in  the  Drum  Lummon  lode  in  Montana.  The 
oxidized  ore  of  upper  levels  includes  frequent  streaks  of  argen- 
tite  and  the  rich  silver  sulphides.  The  lower  levels  show  the 
unchanged  sulphides  of  iron,  copper,  lead  and  zinc.  The 
gangue  is  quartz,  carrying  in  the  ore-bodies  occasional  clay- 
streaks,  heavily  stained  with  the  hydrated  oxides  of  iron  and 
manganese.  Other  accompanying  minerals  found  less  fre- 
quently are  polybasite,  embolite,  etc.  The  vein-material  is 
quartz  pure  and  simple.  The  foot-wall  is  usually  decomposed 
and  broken,  and  a  clay  parting  often  runs  a  foot  or  two  inside 
of  the  wall,  necessitating  close  stulling  till  the  stope  can  be 
filled  with  waste.  The  conditions  noted  here  are  the  counter- 
part of  those  encountered  in  the  copper-veins  of  Butte,  where 
later  fractures,  marked  by  clay  and  attrition-breccia,  have  been 
the  channels  for  enriching  solutions. 

The  Secondary  Enrichment  of  Veins  at  Neihart,  Montana. 
Secondary  enrichment  has  played  an  unusually  important 
part  in  the  development  of  the  ore-deposits  of  Neihart.  The 
ores  extracted  in  the  earlier  workings  and  those  found  to-day 
where  new  veins  are  opened,  all  show  silver  sulphides  deposited 
by  secondary  enrichment  as  crusts  or  crystals  lining  cavities, 
or  as  films  or  thin  coatings  along  fractures  of  the  primary  ore, 
or  in  the  oxidized  zone  as  the  so-called  "  sooty  sulphide  "  ores 
that  occur  with  manganese  oxides.  It  is  from  this  zone  of 
enrichment  that  the  high-grade  ores,  running  from  200  to  1000 
ounces  of  silver  to  the  ton,  or  even  higher,  were  obtained  in 
the  early  history  of  the  camp.  Although  such  ores  gave  out 
in  depth  and  caused  many  disappointments  and  failures,  their 
occurrence  played  a  most  beneficial  part  in  the  development  of 
the  veins. 

*  Trans.,  xvii.,  432. 


494 


ENRICHMENT    OF    GOLD    AND    SILVER    VEINS. 


The  secondary  minerals  recognized  are  chiefly  polybasite 
(really  pearcite)  and  ruby-silver,  the  former  being  more  abun- 
dant. There  are  also  bright  metallic  coatings,  presumably  ar- 
gentite,  on  crystals  and  along  fracture-planes,  and  rarely  in 
minutely  crystalline  masses.  The  superficial  alteration  of  the 
Neihart  veins  is  not  a  marked  one,  as  there  are  no  great  zones 
of  carbonates  and  oxidized  ore.  Such  ores  occur  only  in  limited 
amounts,  being  most  abundant  in  the  Broadwater  vein,  where 

FIG.  9. 


€1  =  Black  "clay"  M  seam:  Colored  by  ground  up  galena  etc. 

J  =  White  spar  stippled  with  galena,  pyrite  and  blende. 

C  =  Secondary  fault-fissure  in  primary  ore.  Filled  by  clay  holding 

ore  fragments. 

(L  =  Shattered  "spar"  ore,  galena  etc. 
e  =  Secondary  fault-fissure  traversing  vein:  The  clay  filling  is  black  and 

holds  secondary  antimonial  sulphides  of  silver  making  good  ore. 
J*  =  Shattered  ^and  altered  gneiss  holding  films  of  rich  sulphide  ore  and^ 

vugs  of  ^"across  holding  rich  silver  sulphides. 
ff  =  Gneiss 
h  =  Vein  of  polybasite 

Face  of  Broadwater  Vein  Exposed  August,  1897,  on  Stope  Below  Third  Level. 

the  partially  oxidized  ores  extend  down  170  feet  below  the  out- 
crop, and,  in  pipes  and  along  drainage  fissures,  reach  even 
greater  depths.  Generally,  however,  there  is  another  zone  of 
alteration  below  the  level  of  these  altered  or  highly  altered 
ores — the  zone  of  enrichment.  This  secondary  ore  also  occurs 
in  the  cracks  of  the  shattered  country-rock,  forming  the  vein- 
matter  where  it  is  associated  with  secondary  quartz  (Fig.  9). 
Very  commonly  the  polybasite  occurs  in  crystalline  masses 
showing  no  definite  crystal  outlines.  In  the  open  spaces  and 


ENRICHMENT    OF    GOLD    AND    SILVER    VEINS.  495 

vugs  of  the  vein,  crystallized  specimens  have  been  found  associ- 
ated with  barite.  It  is  possible,  of  course,  that  this  may  be  due 
to  the  meeting  of  surface-  and  of  deep-seated  waters.  The  zones 
of  impoverishment,  of  enrichment,  and  of  unaltered  primary 
sulphides  recognized  in  the  case  of  the  copper  veins  are  clearly 
present  here,  though  the  uppermost  is  of  limited  extent,  and 
the  zones  are  not  so  sharply  or  definitely  separated  from  one 
another  as  they  are  in  copper  deposits,  owing  to  the  later 
fissuring  of  the  vein-filling  allowing  the  secondary  enrichment 
to  be  mixed  with  the  unaltered  sulphides.  Polybasite  is  said 
by  Dana  to  alter  to  stephanite  and  pyrite.  In  the  Neihart  ores 
the  mineral  seems  to  show  an  alteration  to  pyrargyrite  and 
pyrite,  and  the  former,  in  turn,  changes  to  native  silver  in  the 
upper  zone. 

An  example  of  the  economic  necessity  of  carefully  observing 
secondary  fractures  and  accompanying  enrichment  is  shown  by 
the  Eva  May  mine,  on  Cataract  creek,  near  Boulder,  Montana. 
In  the  early  history  of  the  mine  much  high-grade  ore  was  found 
consisting  of  pyrite,  together  with  more  or  less  galena,  blende 
and  chalcopyrite,  the  whole  impregnated  with  scattered  bunches 
of  rich  antimonial  sulphides  of  silver.  The  vein  is  a  large 
one  and  shows  thick  ore-shoots  of  pyritic  ore,  but  the  bulk  of 
this  away  from  the  enriching  fracture  is  too  poor  to  work. 
Concentrates  made  from  it  have,  according  to  analysis  in  the 
Survey  laboratory,  the  composition  shown  under  I.  in  the  fol- 
lowing Table : 


I. 

II. 

Per  cent. 

Per  cent. 

Silica,  Alumina,  etc.     j^^le, 
/  Part  of  ore,       . 

.       19.81 
.50 

10.31 
.56 

Fe,         

.      24.08 

23.59 

Pb,         

9.83 

23.93 

Zn,         .         .         .         .         . 

6.00 

5.74 

Cu,         .        .        .        .-.       .      .,        . 

....        4.56 

1.29 

Bi,         . 

.33 

.12 

Ni,         .        .        .        .        .      ...        . 

.03 

trace 

Ca,          .        .        T       .         .        .       •', 

none 

As,         ,       ..        ,    /  V       *        .        . 

2.01 

.98 

Sb,         .      -.••-.    ,        .        ... 

.55 

trace 

s 

32  30 

33.48 

100.00  100.00 

Gold,  ounces  per  ton, .10  .75 

Silver,      "      "".....        1.85  7.25 


496  ENRICHMENT    OF   GOLD   AND    SILVEE   VEINS. 

This  material,  which  looks  so  much  like  good  ore,  has  caused 
the  mine  to  shut  down.  It  will  be  seen  that  it  furnishes  an 
admirable  material  for  alteration  and  concentration  of  silver 
according  to  the  process  outlined  in  the  first  part  of  this  paper. 
In  point  of  fact  the  pay-streaks  and  pay  ore-bodies  of  this 
property  are  of  secondary  origin,  and  it  is  only  by  confining 
mining  operations  to  such  places  that  the  mine  can  be  made 
to  pay. 

Another  example  is  the  Frohner  mine,  10  miles  south  of 
Helena,  at  the  head  of  Clancey  creek.  The  main  ore  is  a  mix- 
ture of  galena  and  pyrite,  and  occurs  in  sufficient  abundance  to 
warrant  working,  if  it  were  not  too  low  in  grade.  Yet  the 
primary  ore,  where  not  enriched,  will  not  pay  for  concentra- 
tion. The  composition  of  this  ore  is  given  in  column  II.  of 
the  table  on  the  preceding  page.  The  ore  has  been  concen- 
trated until  it  carries  but  10.3  per  cent,  silica,  with  iron  and 
lead  present  in  nearly  equal  proportions.  The  sample  was 
carefully  collected,  so  as  to  represent  a  true  average  of  the  con- 
centrates as  shipped.  The  rich  ore  of  the  mine,  carrying  as 
high  as  200  oz.  of  silver  per  ton,  was  found  near  secondary  frac- 
tures, and  consisted,  I  am  told,  of  pyrite  and  galena  with  films 
and  nests  of  antimonial  sulphides  of  silver. 

A  considerable  list  of  mines  in  Montana  might  be  mentioned 
in  which  such  phenomena  have  been  observed  by  the  writer. 
Of  many  others  the  past  history  shows  rich  surface-ores,  be- 
coming rapidly  leaner  in  depth.  This  is  true  not  only  of  silver 
mines,  but  of  gold-silver  properties,  near  Marysville,  Montana, 
in  California  at  the  Mojave  mines,  etc. 

Where  telluride  ores  occur,  the  only  enrichment  observed 
has  been  due  to  superficial  alteration,  as  has  been  observed  in 
the  Judith  mountains,  Little  Rocky  mountains,  the  Dolcoath 
mine  near  Elkhorn,  and  the  Mayflower  mine,  all  in  Montana. 

The  Effect  of  Physiographic  and  Climatic  Changes. 
Active  degradation  favors  the  accumulation  of  enrichments, 
while  prolonged  degradation  of  a  region,  resulting  from  phys- 
iographic revolutions,  may  result  in  successive  migrations  of 
material  and  the  accumulation  in  a  relatively  shallow  zone  of 
the  metals  derived  from  many  hundreds,  and  possibly  thou- 
sands, of  feet  of  the  vein  worn  away  in  the  degradation  of  the 


ENRICHMENT    OF    GOLD    AND    SILVER    VEINS.  497 

land.  Climatic  conditions,  rainfall  or  aridity,  warmth  and 
rapid  alteration  of  vein  fracture  are  agents  affecting  surface- 
weathering,  and  hence,  also,  enrichment. 

Active  degradation  of  a  region,  that  is,  rapid  weathering, 
favors  enrichment  by  the  quickness  with  which  it  removes  the 
upper  already  leached  part  of  the  vein,  so  that  a  larger  amount 
of  vein  matter  is  lixiviated  in  a  given  time  than  would  result 
from  slower  wasting  of  the  land.  Such  enrichments  are 
favored  by  high  altitudes.  Moreover,  the  mountainous  regions 
are  those  in  which  secondary  fractures  are  most  apt  to  be 

found. 

Changes  of  Water-Level. 

Prolonged  degradation  is  favorable  for  a  similar  reason,  since 
time  is  a  factor  in  enrichment,  and  changes  in  elevation,  etc., 
affect  the  rate  and  progress  of  decay  of  the  vein;  while  the 
crustal  movements  accompanying  physiographic  changes  favor 
fractures    of    the    earlier    deposit,   which   give   facilities   for 
leaching  and  spaces  for  deposition.    If  a  region  passes  through 
several  cycles  of  erosion  and  elevation,  it  is  evident  that  their 
result  is  likely  to  be  a  succession  of  enrichments  in  which 
not  only  the  original  ore  is  leached,  but  the  earlier  enrichment- 
deposits  migrate  downward.     At  Butte,  Montana,  the  region 
has  passed  through  several  very  pronounced  changes  in  eleva- 
tion since  the  formation  of  the  veins  in  tertiary  time.     In  early 
Tertiary  time  the  present  topography  was  blocked  out,  and  the 
mountain  ranges  and  deep  intervening  valleys  were   carved. 
This  was  succeeded  by  earth-movements  by  which  the  streams 
became  clogged  or  the  valleys  dammed,  forming  lakes ;  while 
volcanoes  broke  out  at  numerous  places  and  showered  ashes 
and  scoria  over  the  region.     The  valleys  were  silted  up  or  in 
part  filled  by  volcanic  debris,  before  crustal  movements  drained 
the  valleys  and  altered  the  divides.     More  recent  movement, 
possibly  still  continuing,  is  marked  by  faults  and  a  reversing 
of  stream-courses.     The  old  valley  at  Butte  is  filled  by  hun- 
dreds of  feet  of  debris,  and  a  mountain  wall  2500  feet  high 
marks  a  north  and  south  fault-line.     These  changes  all  caused 
a  migration  of  water-level  facilitating  the  processes  of  weather- 
ing and  enrichment,  and  the  great  bodies  of  rich  copper-ores 
of  the  region  are  believed  to  be  in  part  due  to  this  cause. 


498  METASOMATIC    PROCESSES   IN   FISSURE-VEINS. 


Metasomatic  Processes  in  Fissure-Veins.* 

BY  WALDEMAR  LINDGREN,   WASHINGTON,   D.    C. 

(Washington  Meeting,  February,  1900.) 
CONTENTS. 

PART  I. — GENERAL  FEATURES. 

PAGE 

Purpose  and  Extent  of  Inquiry  ;  Definitions  (Fissure- Veins,  Metamorphism, 
Metasomatism,  Impregnation,  Cementation,  Weathering);  Metasomatism 
in  Connection  with  Mineral  Deposits,  Especially  Fissure-Veins  ;  Calcu- 
lation of  Analyses  ;  Criteria  of  Metasomatism ;  Crystallization  of  Sec- 
ondary Minerals  in  Other  Bodies ;  Secondary  Alteration  of  Veins ; 
Structure  and  Composition  of  Metasomatic  Vein-Kocks  and  Their  Kela- 
tion  to  General  Metamorphism, 499 

PART  II. — MINERALS  DEVELOPED  BY  METASOMATIC  PROCESSES 
IN  FISSURE-VEINS. 

Quartz,  including  Chalcedonite  and  Opal ;  Eutile  and  Anatase  ;  Fluorite  ; 
Calcite  ;  Magnesite  and  Dolomite  ;  Siderite  ;  Muscovite  and  Sericite ; 
Biotite  ;  Chlorite  ;  Pyroxene  and  Amphibole  ;  Garnet ;  Epidote  ;  Ortho- 
clase  ;  Albite  ;  Tourmaline  ;  Topaz  ;  Kaolinite  ;  Zeolites  ;  Pyrite  ;  Mar- 
casite  ;  Chalcopyrite  ;  Arsenopyrite  ;  Pyrrhotite  ;  Galena ;  Zinc-blende 
and  Other  Sulphides ;  Tellurides ;  Native  Copper  ;  Gold  and  Silver,  .  521 

Kesistant  Minerals, 539 

PART  III. — THE  FISSURE-VEINS  CLASSIFIED  ACCORDING  TO 
METASOMATIC  PROCESSES. 

1.  Topaz-Cassiterite  Veins  (Altenberg  and  Zinnwald,  Saxony  ;  Mt.  Bischoff, 

Tasmania),       ............  540 

2.  Scapolite- Apatite  Veins,     .        .         .        .        '&     .        ...        .545 

3.  Tourmalinic  Gold-Copper  Veins,       .         .         .         .         .         *         .         .  546 

4.  Biotitic  Gold-Copper  Veins, •,......  564 

5.  Propylitic  Gold  and  Silver  Veins  ( General  Features ;  Comstock  Lode ; 

The  Veins  of  Nagyag,   Hungary ;    Pachuca,   Mexico  ;    New  Zealand  ; 
Alaska  ;  Silver  Cliff,  Colorado ;  Silver  City,  Idaho),       .        .        *         .565 

6.  Flnoritic  Gold-Tellurium  Veins  (Cripple  Creek  ;  Other  Occurrences),      .  574 

7.  Sericitic  and  Kaolinitic  Gold-  and  Silver-Veins  (General  Kemarks  ;  The 

Freiberg  Veins  ;  De  Lamar,  Idaho  ;  Summit  District,  Colorado),  .         .  578 

8.  Sericitic  and  Calcitic  Gold-Silver  Veins  (The  Gold-Quartz  Veins  of  Cali- 

fornia ;  Idaho  Types ;  San  Juan,  Colorado  ;   Treadwell  Mine,  Alaska  ; 
Gold  Veins  of  Ontario,  Canada  ;  Schwarzwald  Fissure-Veins),       .         .  584 

*  Presented  by  permission  of  the  Director  of  the  U.  S.  Geological  Survey. 


METASOMATIC    PROCESSES   IN   FISSURE-VEINS.  499 

PAGE 
9.  Silicic  and  Calcitic  Cinnabar- Veins, 595 

10.  Sericitic  Copper-Silver  Veins, .596 

11.  Silicic  and  Dolomitic  Silver-Lead  Veins  (Aspen,  Colorado),  .         .  596 

12.  Sideritic  Silver-Lead  Veins  (Wood  Kiver,  Idaho  ;  Cceur  d'Alene  Moun- 
tains, Idaho), ...  599 

13.  Sericitic   Silver-Lead   Veins    (Clausthal  Veins;    The  Democrat  Vein, 
Hailey,  Idaho), 602 

14.  Zeolitic  Copper-Veins, 606 

Observed  Alteration  by  Ascending  Waters, 608 

Conclusions,        ...........  609 


PART  I. 

GENERAL  FEATURES. 

Purpose  and  Extent  of  Inquiry. 

A  study  of  the  changes  in  rocks  contiguous  to  ore-bearing 
fissures  is  essential  to  a  thorough  understanding  of  the  genesis 
of  such  deposits.  Nevertheless,  comparatively  little  work  has 
been  done  in  this  direction,  though  many  mining  geologists  (for 
instance,  v.  Groddeck)  long  ago  emphatically  declared  the  neces- 
sity of  such  investigations.  Ores  and  structure  have  been  dealt 
with  in  detail ;  but  the  important  changes  which  adjacent  rocks 
of  known  composition  have  suffered  are  too  often  briefly  dis- 
missed, or  even  incorrectly  indicated.  It  is  the  purpose  of  this 
review  to  collect  the  scattered  data  relating  to  the  alteration  of 
rocks  near  or  between  fissures ;  to  indicate  the  principal  active 
processes;  to  classify  the  veins,  if  possible,  according  to  the 
different  phases  of  alteration  accompanying  them ;  and,  finally, 
to  draw  some  conclusions  from  the  facts  thus  grouped.  This 
first  attempt  to  systematize  the  metasomatic  data  of  fissure- 
veins  is  by  no  means  complete  :  only  such  parts  of  the  American 
and  foreign  literature  are  represented  as  were  deemed  to  be 
of  vital  importance.  The  discussion  principally  involves  the 
changes  which  the  country-rock  has  undergone,  whether  they 
have  resulted  in  the  formation  of  ores  or  not ;  and,  in  the  sec- 
ond place,  some  space  is  devoted  to  such  alterations  as  fissure- 
veins  already  formed  sometimes  suffer  through  certain  sec- 
ondary agencies.  I  have  excluded,  however,  all  references  to 
weathering,  or  to  the  decomposition  of  vein-materials  near  the 
surface  by  waters  containing  free  oxygen.  It  is  often  difficult 
to  draw  the  line  between  normal  fissure-veins  and  deposits  not 

32 


500  METASOMATIC    PROCESSES   IN    FISSURE-VEINS. 

to  be  regarded  as  such,  strictly  speaking,  but  clearly  due  to  the 
same  genetic  causes ;  and  some  of  the  latter  class  have  been 
included  in  this  discussion. 

Definitions. 

Fissure- Veins. — For  the  present  discussion,  a  fissure-vein  may 
be  regarded  as  a  mineral  mass,  tabular  in  form,  as  a  whole, 
though  frequently  irregular  in  detail,  occupying  or  accompany- 
ing a  fracture  or  set  of  fractures  in  the  enclosing  rock;  this 
mineral  mass  has  been  formed  later  than  the  country-rock  and 
the  fracture,  either  through  the  filling  of  open  spaces  along  the 
latter,  or  through  chemical  alteration  of  the  adjoining  rock. 
Such  alteration  does  not  ordinarily  extend  far  from  the  fissure. 
Only  in  regions  where  the  vein-forming  agencies  have  acted 
with  unusual  intensity,  a  partial  alteration  may  extend  over 
larger  areas.  These  zones  of  alteration  being  genetically  con- 
nected with  the  veins  proper,  must  necessarily  also  be  consid- 
ered in  this  discussion. 

Metamorphism. — This  term,  meaning  strictly  a  change  of 
form,  was  proposed  by  Lyell  in  1831,  and  has  since  been  em- 
ployed in  a  wider  sense,  so  as  to  cover  any  change  in  the  com- 
position or  structure  of  a  rock,  through  whatever  agency,  and 
whether  with  or  without  gain  or  loss  of  substance. 

Metasomatism. — This  name,  meaning  a  "  change  of  body,"  is 
given  to  that  variety  of  metamorphism  which  involves  a  change 
in  the  chemical  composition  of  rocks,  by  the  addition  or  sub- 
traction of  substance.*  The  terms  "  replacement,"  "  substitu- 
tion," "  alteration,"  etc.,  have  been  employed  in  discussions  of 
metasomatism  with  different  shades  of  meaning.  A  review  of 
the  classification  of  pseudomorphs,  which  form  the  origin  of 
our  knowledge  of  metasomatism,  will  throw  light  upon  the 
nomenclature  of  the  subject. 

The  occurrence  of  organic  remains,  consisting  of  material  of 
which  they  were  certainly  not  originally  composed,  called  atten- 
tion to  the  remarkable  transformations  now  known  as  meta- 
somatic  replacements.  As  instances,  we  may  recall  corals 
changed  into  quartz,  belemnites  converted  into  barite,  and  shells 
of  bivalves  or  gasteropods  transformed  into  pyrite,  chalcocite, 

*  Dana  (Man.  of  GeoL,  4th  ed.,  p.  314)  proposes  for  the  same  process  the  term 
"  metachemic  ;"  but  this  has  not  found  general  acceptance. 


METASOMATIC    PROCESSES   IN   FISSURE-VEINS.  501 

sphalerite  or  specularite.  To  the  same  order  of  phenomena  be- 
longs the  silicified  wood,  in  which  the  organic  substance  has 
been  removed  and  replaced  with  silica  so  delicately  as  to  pre- 
serve in  minute  detail  the  original  organic  structure.  This  re- 
placement is  probably  due  to  the  precipitation  of  silica  from  so- 
lution by  the  acids  generated  in  the  decay  of  organic  matter. 
More  rarely,  wood  and  plant-remains  may  be  replaced  by  py- 
rite,  chalcocite,  galenite,  cinnabar,  barite,  limonite,  malachite, 
etc. 

But  it  is  the  study  of  pseudomorphs,  showing  one  mineral 
appearing  in  the  crystal-form  of  another,  that  has  led  to  a  more 
detailed  knowledge  of  the  chemical  laws  which  govern  these 
remarkable  changes.  Here  was  conclusive  proof  that  one  min- 
eral, definitely  crystallized,  had  changed  into  another,  some- 
times totally  different,  substance.  ISTaumann  says  of  pseudo- 
morphs : 

' '  Their  importance  cannot  be  overestimated,  because  they  enable  us  to  study 
successfully  the  laws  of  the  processes  which  are  constantly  acting  in  the  rocks  and 
constantly  changing  them  ;  for  the  pseudomorphs  represent  only  one  special 
case  of  the  grand  process  of  chemical  alteration  going  on  in  the  mineral  kingdom  : 
namely,  that  in  which  the  form  remained  in  spite  of  the  change.  From  these  we 
may  draw  conclusions  as  to  the  chemical  processes  going  on  in  rocks  which  may 
change  each  grain  to  another  mineral."* 

Blum,  who  made  the  first  extensive  examination  of  pseudo- 
morphs, divided  them  into:  (1)  those  produced  by  partial 
change  in  the  composition  of  the  original  mineral  (one  or  more 
elements  being  removed,  added  or  introduced  by  substitution) ; 
and  (2)  those  produced  by  a  complete  replacement  of  the  orig- 
inal mineral  with  another.  (This  class  includes  both  those 
produced  by  chemical  replacement  and  by  previous  solution 
and  subsequent  filling.) 

Naumann,  in  his  well-known  text-book  of  Mineralogy,  di- 
vided the  pseudomorphs  into :  (1)  hypostatic  pseudomorphs, 
formed  by  the  mechanical  deposition  of  substance  outwards  or 
inwards  from  the  limiting  planes,  and  again  subdivided  into 
pseudomorphs  by  covering,  and  pseudomorphs  by  filling ;  (2) 
metasomatic  pseudomorphs,  formed  by  the  alteration  of  the 
substance  by  means  of  its  molecular  replacement  with  another 
mineral  while  the  form  has  been  preserved.  The  metasomatic 

*  Minercdogie,  Naumann-Zirkel,  10th  ed.,  Leipzig,  p.  112. 


502  METASOMATIC    PROCESSES   IN   FISSURE-VEINS. 

pseudomorphs  are  also  designated  as  "  alteration  "  ( Umwand- 
lung)  pseudomorphs.  This,  it  will  be  noted,  is  the  first  intro- 
duction of  the  word  metasomatic  in  technical  literature.  In 
nearly  all  cases,  the  metasomatic  pseudomorphs  involve  chem- 
ical action. 

I^aumann  further  divides  the  metasomatic  pseudomorphs  into 
three  classes,  in  which,  respectively,  (a)  the  original  and  the 
secondary  substance  are  identical  in  chemical  constituents 
("  paramorphic "  pseudomorphs) ;  or  (b)  chemical  alteration 
has  left  one  or  more  elements  of  the  original  in  the  secondary 
substance ;  or  (c)  the  replacement  of  constituents  has  been  com- 
plete, as  in  the  substitution  of  galenite  for  calcite,  or  pyrite 
for  quartz,  but  the  process  has  been,  nevertheless,  a  chemical 
one,  since  the  removal  and  deposition  have  proceeded  simul- 
taneously, molecule  for  molecule.  The  second  of  these  classes 
is  again  subdivided,  according  as  the  change  involved  simply 
the  loss  of  original  components  (as  in  the  formation  of  argen- 
tite  from  pyrargyrite),  or  the  addition  of  components  (e.g.,  angle- 
site  from  galenite),  or  the  exchange  of  components  (e.g.,  sericite 
from  oligoclase). 

The  conceptions  of  Blum  were  introduced  into  English 
technical  literature  by  James  D.  Dana,*  who  divided  pseudo- 
morphs into  those  formed :  (1)  by  infiltration  (mechanical  de- 
position in  a  mould  already  formed) ;  (2)  by  incrustation  (me- 
chanical covering  of  crystals) ;  (3)  by  replacement,  one  mineral 
gradually  replacing  another,  and  assuming  at  the  same  time  its 
form,  without  any  interchange  of  elements  (the  process  being 
in  a  certain  sense  chemical,  and  wholly  diiferent  from  simple 
deposition) ;  (4)  by  alteration,  some  of  the  elements  being  re- 
moved or  exchanged,  or  new  ones  being  added;  and  (5)  by 
allomorphism,  without  chemical  alteration ;  the  body  changing 
to  one  of  the  same  composition  but  of  different  crystallographic 
system  (the  paramorphic  pseudomorphs  of  Naumann). 

Somewhat  extreme  views,  differing  from  the  above,  were 
advanced  by  T.  Sterry  Hunt,f  who  classed  pseudomorphs  as  : 
(1)  those  produced  by  chemical  alteration,  meaning  by  this  a 
partial  exchange  of  constituents  (e.g.,  limonite  after  siderite); 
and  (2)  those  produced  by  substitution  or  replacement  (these 

*  American  Journal  of  Science,  vol.  48,  1845,  p.  81. 
f  Systematic  Mineralogy,  New  York,  1892,  p.  111. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  503 

terms  being  evidently  regarded  as  equivalent).  The  latter  he 
believed  to  be  produced  by  deposition  in  spaces  left  by  the  re- 
moval of  some  other  matter.  The  form  of  the  original  sub- 
stance is  assumed  by  the  material  which  displaces,  or  is  substi- 
tuted for  it,  e.g.,  quartz  after  calcite,  barite,  etc.  While  thus 
admitting  partial  alterations,  Hunt  makes  a  special  case  of  a 
complete  replacement,  refusing  to  consider  it  as  a  chemical 
process,  and  regarding  it  always  as  an  instance  of  separate  dis- 
solving and  refilling.  To  the  theory  of  metasomatism,  which 
maintains  that  all  the  chemical  elements  in  a  crystal  may  be 
removed,  and  by  molecular  processes  replaced  with  foreign 
substances,  Sterry  Hunt  was  strongly  opposed. 

Pseudomorphs  of  the  second  group  proposed  by  him  are,  as 
is  well  known,  of  frequent  occurrence,  and  correspond  to  Nau- 
mann's  hypostatic  division  or  pseudomorphs  formed  by  me- 
chanical deposition.  Spaces  of  dissolution,  subsequently  filled, 
are  also  common  enough  in  rocks,  and  may  usually  be  readily 
identified  as  such  under  the  microscope.  But  that  molecular 
replacement,  as  defined  by  Naumann  and  Dana,  also  exists, 
and,  moreover,  is  of  the  highest  importance,  seems  at  present 
beyond  doubt. 

As  the  essential  process  of  metasomatism  applies  as  well  to 
an  irregular  grain  as  to  a  perfectly  developed  crystal,  we  are 
justified  in  extending  the  conception  to  aggregates  of  grains  of 
one  or  several  minerals ;  in  other  words,  to  rocks  and  mineral 
aggregates  in  general.  In  this  sense  C.  R.  Van  Hise*  has  de- 
fined metasomatism  as  "  the  process  of  metamorphism  by  which 
original  minerals  are  partly  or  wholly  altered  into  other  min- 
erals, or  are  replaced  by  other  minerals,  or  are  recrystallized 
without  chemical  changes,  or  one  or  all  of  these  together."  S. 
F.  Emmons  has  defined  metasomatism  as  follows :  f 

' '  By  metasomatic  exchange  is  meant  an  interchange  of  substance  without  nec- 
essarily involving,  as  does  pseudomorphism,  the  preservation  of  the  original  form 
of  the  substance  replaced,  or  even  of  its  original  volume." 

A  second  definition,  based  on  the  consideration  that  practically 
simultaneous  solution  and  deposition  could  certainly  be  proved 

*  "  Principles  of  Pre-Cambrian  Geology,"  16^  Ann.  Rept.,  U.  S.  Geol.  Sur., 
parti.,  p.  689. 

f   U.  S.  Geol.  Surv.,  Monogr.  XII.,  p.  565. 


504  METASOMATIC    PROCESSES   IN    FISSURE-VEINS. 

for  many  cases,  where  the  exact  proof  of  chemical-molecular 
replacement  could  not  be  furnished,  is  given  by  Mr.  Emmons 
as  follows :  * 

"  By  metasomatic  interchange  I  understand  an  interchange  of  substances,  but 
not  necessarily  molecule  by  molecule,  in  such  a  manner  as  to  preserve  the  original 
structure,  form  or  volume  of  the  substance  replaced." 

The  fundamental  difficulty  is  that  the  final  result  does  not 
always  indicate  the  particular  pseudomorphic  process  which  has 
preceded.  Mechanical  deposition,  for  instance,  may  follow  so 
closely  after  dissolution,  that  the  two  processes  really  appear  as 
one.  It  may  also  be  said  that  molecular  replacement  is  diffi- 
cult to  prove,  as  molecular  processes  cannot  be  followed  with 
the  microscope ;  and  this  is,  in  a  sense,  true.  We  may  assert, 
however,  that,  with  the  highest  magnifying  powers,  we  are  able 
to  follow  the  transformation  of  quartz,  for  instance,  into  seri- 
cite,  or  into  calcite,  or  into  siderite,  without  finding  the 
slightest  indication  of  an  intermediate  stage  of  open  space. 
The  fiber  and  blades  of  sericite  project  into  the  quartz  without 
the  slightest  break  in  the  contact ;  the  rhombohedrons  of  sider- 
ite develop  in  quartzite,  their  crystal  faces  cutting  across  the 
grains  without  any  interstices.  Perfect  tourmaline  prisms  de- 
velop in  feldspar  grains,  and  sharp  cubes  of  pyrite  in  primary 
granitic  quartz. 

In  cases  of  complete  molecular  replacement,  such  as  galena 
after  calcite,  the  replacing  mineral  was  probably  present  in  the 
solution,  partly  dissociated  or  ionized.  The  solution  of  a  cer- 
tain quantity  of  the  original  mineral  caused  the  separation  of  a 
corresponding  quantity  of  the  ions  of  the  replacing  substance, 
according  to  physico-chemical  laws.  If  carried  out  on  these 
lines,  the  process  is  necessarily  molecular  and  chemical.  Where 
there  were  two  solutions — one  dissolving,  the  other  depositing 
— and  where  a  certain  time  intervened,  the  process  is  a  mechan- 
ical one  and  should  not,  I  think,  be  considered  metasomatic. 
In  many  cases  the  distinction  may  be  very  difficult  to  draw. 

In  conclusion,  metasomatism  might  be  defined  as  the  pro- 
cess by  which  a  mineral  has  suffered,  through  chemical  pro- 
cesses, a  partial  or  complete  change  in  its  chemical  constitution. 
Rocks  or  aggregates  of  minerals  are  "  metasomatic,"  if  any  or 

*  "The  Genesis  of  Certain  Ore-Deposits,"  Trans.,  xv.,  128,  1886. 


METASOMATIC    PROCESSES   IN   FISSURE-VEINS.  505 

all  of  the  constituent  minerals  have  undergone  such  changes. 
This  definition  excludes  the  process  of  paramorphism  which,  as 
already  emphasized  by  Naumann,  is  exceedingly  rare. 

In  the  use  of  the  term  alteration  it  would  perhaps  be  best  to 
follow  Dana  and  let  it  mean  a  partial  change  of  substance  in  a 
mineral  or  rock.  Decomposition,  it  would  seem  advisable  to  re- 
strict to  the  cases  in  which  a  mineral  or  rock  is  dissolved  into 
its  component  parts ;  and  a  principal  use  for  it  would  be  found 
in  the  processes  of  weathering. 

As  has  been  shown,  the  words  replacement  and  substitution 
have  been  used  in  very  different  ways.  The  majority  of  recent 
authors  use  them  both  as  equivalent  to  metasomatism.  Dana, 
however,  applies  replacement  to  a  complete  exchange  of  sub- 
stance, reserving  alteration  for  a  partial  loss,  gain  or  interchange 
of  elements ;  while  Sterry  Hunt  gives  the  name  of  replacement 
or  substitution  to  mechanical  dissolution  and  the  filling  of  the 
resultant  cavities. 

The  chemist  has,  however,  a  distinct  definition  of  substitution 
as  "  the  replacing  of  one  or  more  elements  or  radicals  in  a 
compound  by  other  elements  or  compounds;"  and  it  would 
probably  be  best  to  adhere  to  this,  and  discard  substitution  as  a 
synonym  for  metasomatism  or  alteration. 

Replacement  is,  in  its  general  meaning,  nearly  identical  with 
substitution,  although  it  has  no  such  distinct  chemical  use.  It 
would  seem  advisable  to  regard  it  as  a  synonym  of  metasoma- 
tism, distinguishing,  for  the  sake  of  convenience,  between  par- 
tial and  complete  replacement.  This  is  contrary  to  Dana's  dis- 
tinction ;  but  the  word  has  been  used  so  generally  during  late 
years  in  this  wider  sense  that  it  seems  best  to  retain  this  mean- 
ing for  it. 

Impregnation. — This  term  has  been  applied  in  so  many  differ- 
ent ways — to  primary  disseminations ;  to  minerals  formed  by 
replacement ;  and  to  the  filling  of  cavities  or  interstitial  spaces 
in  rocks — that  it  might  well  be  rejected  altogether  as  a  genetic 
term,  and  used  only  in  a  structural  sense,  as  descriptive  of 
finely  divided  material  disseminated  in  a  differing  mineral  or 
rock-mass. 

Cementation. — This  term,  proposed  by  Prof.  C.  R.  Van  Hise,* 

*  "  Pre-Cambrian  Geology."     IQth  Ann.  Report  U.  S.  G.  S.,  part  i.,  p.  684. 


506  METASOMATIC    PROCESSES   IN   FISSURE-VEINS. 

is  convenient  and  expressive  for  the  purpose  of  indicating  fill- 
ing of  interstices  in  porous  or  shattered  rocks.  Cementation 
assumes  importance  in  proportion  to  the  porosity  of  the  rock, 
which,  in  sandstones  and  tuffs,  may  reach  10  or  20  per  cent. 
In  most  intrusive  igneous  rocks  the  porosity  is  so  small  as  to  be 
a  negligible  quantity. 

Weathering. — Under  this  name  are  included  the  changes  of 
rocks  near  the  surface  in  cohesion  and  composition,  due  to  the 
decomposing  and  oxidizing  action  of  percolating  waters  above 
the  permanent  water-level.  The  tendency  of  weathering  is  to 
destroy  the  rock  as  a  geological  unit.  The  final  results  of 
metasomatic  action  are  a  few  resistant  minerals,  such  as  quartz, 
kaolin  and  limonite.  The  formation  of  serpentine,  chlorite, 
epidote  and  (ordinarily)  pyrite  is  not  weathering,  but  is  due  to 
more  deeply  seated  causes.  The  German  usage  of  Verwitterung r, 
to  cover  all  secondary  changes,  due  to  weathering,  thermal  and 
other  causes,  seems  highly  objectionable,  and  especially  apt  to 
lead  to  many  misconceptions. 

In  view  of  the  difference  of  usage  as  to  many  of  the  above 
definitions,  it  is  to  be  hoped  that  writers  upon  this  subject  will 
take  pains  to  indicate  the  sense  in  which  the  various  terms  are 
employed  by  them. 

Metasomatism  in  Connection  with  Mineral  Deposits,  Especially 
Fissure-  Veins. 

It  was  not  long  before  the  principles  of  metasomatic  action, 
learned  by  the  study  of  pseudomorphs,  were  applied  to  larger 
masses  of  rocks.  This  led,  perhaps  inevitably,  to  exaggerated 
notions,  such  as  that  of  the  formation  of  true  granites  from 
sediments  and  limestone,*  etc. ;  and  this  undue  extension  was 
followed  by  a  reaction,  exemplified  in  Sterry  Hunt's  writings. 

The  observation  that  ores  may  be  found,  not  only  in  the 
clearly  defined  vein-filling,  but  also  in  the  rock  adjacent  to  the 
fissure,  is  contemporaneous  with  almost  the  earliest  scientific 
records  of  mining.  Sandbergerf  mentions  the  occurrence  of 
masses  of  native  silver,  found  in  1786  in  the  altered  granite  of 
certain  Schwarzwald  veins,  which  greatly  astonished  the  old 
miners.  Yogelgesang,J  in  Cotta's  "  G-angstudien,"  describes 

*  G.  Bischof,  Chem.  Geol,  Bonn,  1866,  vol.  iii.,  p.  34. 

f  Erzgange,  part  ii.,  p  418.  J  Vol.  ii.,  Freiberg,  1854,  p.  78. 


METASOMATIC    PROCESSES   IN   FISSURE-VEINS.  507 

the  dissemination  of  argentite,  native  silver,  and  various  sul- 
phides, in  the  gneiss  adjoining  certain  veins  near  Freiberg. 

But  whether  or  not  it  contains  ore,  the  rock  adjoining  a  vein 
is  very  commonly  softened,  bleached  and  altered  for  some  dis- 
tance away  from  the  fissure.  This  phenomenon  has  been  ex- 
plained in  two  radically  different  ways : 

1.  Bischof  says:* 

"  As  we  find  ores  in  veins,  proportionate  in  quantity  to  the  alteration  of  the 
country-rock,  what  other  relation  can  be  thought  to  exist  between  the  two  facts 
than  that  the  abundance  of  the  ore  is  a  result  of  this  alteration?" 

Sandberger  says  :f 

"The  extent  of  the  alteration  on  both  sides  of  the  vein  corresponds  with  the 
area  from  which  the  products  of  leaching  have  been  carried  to  the  vein." 

2.  The  opponents  of  these  views  say  that  the  narrow  zone  of 
alteration,  intense  next  to  the  fissure  and  gradually  fading  away 
within  a  short  distance  from  it,  most  clearly  indicates  an  agency 
within  the  fissure,  acting  with  gradually  diminishing  energy  on 
the  adjoining  strip  of  rock.     They  also  point  out  that  Bischof  Js 
premise,  i.e.9  the  coincidence  of  richness  of  vein  and  extent  of 
the  altered  zone,  is  not  true  as   a  universal  proposition.     And 
they  show,  further,  that  as  the  whole  altered  zone  has,  in  many 
cases,  received  an  addition  of  the  same  metals  as  are  contained 
in  the  vein  which  may  more  than  counterbalance  its  losses  of 
other  constituents,  Sandberger's  conclusion  can  certainly  not 
have  a  general  application ;  and  finally,  that,  in  those  veins 
which  have  no  gangue,  but  in  which  the  ore  has  accumulated 
in  the  rock  during  the  alteration,  the  incorrectness  of  that  con- 
clusion is  particularly  apparent. 

Veins  carrying  cassiterite  early  attracted  attention,  as  being 
almost  always  accompanied  by  ore  impregnating  the  surround- 
ing country-rock.  The  metasomatic  character  of  the  process 
was  first  shown  by  DaubreeJ  and  later  by  Cotta,§  both  of 
whom,  in  support  of  their  views,  call  attention  to  the  well- 
known  occurrence  of  cassiterite  as  a  pseudomorph  after  feld- 
spar. Both  explain  the  alteration  as  due  to  gradual  replace- 

*  Chem.  Geologic,  Bonn,  1866,  vol.  iii.,  p.  666. 

f  Erzg'dnge,  vol.  i.,  p.  149. 

J  Ann.  d.  Mines,  1841,  xx.,  pp.  65,  72,  83. 

\  Die  Lehre  von  den  Erzlagerstatten,  Freiberg,  1859. 


508  METASOMATIC    PROCESSES   IN   FISSURE-VEINS. 

ment  by  the  agency  of  thermal  waters.  This  explanation  was 
substantiated  by  more  recent  and  detailed  investigations ;  for 
instance,  by  Richard  Pearce  (1864)  and  LeNeve  Foster  (1877) 
in  regard  to  Cornwall ;  and  by  A.  "W.  Stelzner  (1864)  for 
Geyer,  Saxony. 

The  views  of  Gotta  concerning  the  alteration  of  the  wall- 
rocks  or  veins  are  well  expressed  in  the  following  paragraph:* 

11  When  lodes  are  accompanied  by  ore-impregnations,  it  is  to  be  assumed  that 
generally  the  solutions  from  which  the  materials  of  the  lode  were  precipitated — 
they  may  have  been  aqueous,  igneous-fluid,  or  gaseous — also  penetrated  the  wall- 
rock  and  there  caused  certain  deposits  in  fine  clefts  or  in  the  rock  itself.  In  the 
last  case,  crystals  have  made  room  for  themselves  by  their  power  of  crystalliza- 
tion ;  or  an  ore  took  the  place  of  the  mineral  dissolved  ;  for  example,  tin-ore, 
that  of  feldspar." 

This  quotation  shows  plainly  the  clear  conception  which 
Cotta  had  of  the  alteration  of  rocks,  as  due,  not  only  to  filling 
of  pores  and  cracks,  but  also  to  processes  of  replacement  active 
within  the  rocks. 

Although  Cotta  made  no  special  division  of  replacement- 
veins,  he  was  well  aware  of  their  occurrence  and  perfectly  able 
to  distinguish  them  from  filled  spaces.  Describing  the  gold- 
veins  of  Tauern  (Austria), f  he  says  that  they  have  not  the 
character  of  clearly  opened  and  filled  fractures,  but  consist  of 
several  parallel  tight  fissures,  between  which  lies  more  or  less 
impregnated  and  altered  country-rock.  The  gold  penetrates 
into  the  country-rock  from  the  fissure,  and  the  tenor  decreases 
gradually  with  increasing  distance. 

In  1873  Posepny  published  his  famous  examinations  of  the 
Raibl  deposits. J  These  are  not  connected  with  fissures,  but 
deserve  mention,  since  entirely  similar  processes  are  active  in 
fissure-veins.  Posepny  found  that  carbonate  of  zinc  had  re- 
placed carbonate  of  lime  "  by  metamorphic  processes." 

Von  Groddeck,  in  his  well  known  text-book  (1879),  includes 
"  metamorphic  "  deposits  in  his  system,  but  limits  them  to  re- 
placements of  limestone  by  zinc-,  iron-  and  manganese-miner- 
als. At  about  the  same  time,  Stelzner,  in  his  lectures,  intro- 
duced a  corresponding  division  of  "  metasomatic  deposits," 

*  A  Treatise  on  Ore-Deposits.     (Prime's  Translation.)     New  York,  1870,  p.  90. 
t  Die  Lehre  von  den  ErzlagersCdtten,  Freiberg,  1859,  part  ii.,  p.  318. 
%  Jahrbuch  d.  k.k.  Oeol  Keichsanstalt,  xxiii.,  1873',  p.  317. 


METASOMATIC    PROCESSES   IN   FISSURE-VEINS.  509 

though  they  were  still  limited  to  a  relatively  small  number  of 
the  irregular  masses  in  limestone. 

Raphael  Pumpelly  was,  I  believe,  the  first  who  applied  the 
principles  of  metasomatism  to  ore-deposits  in  this  country,  in 
describing  the  copper-deposits  of  Michigan  (in  part  fissure- 
veins)  in  vol.  i.  of  the  Geological  Survey  of  Michigan  (1873), 
and  in  his  noted  paper  on  the  "  Metasomatic  Development  of  the 
Copper-Bearing  Rocks  of  Lake  Superior."*  The  copper,  to  a 
great  extent,  replaces  other  minerals. 

In  1879  J.  A.  Church  published  a  volume  on  the  Comstock 
mines, f  in  which  he  maintained  the  origin  of  the  quartz  by 
replacement  acting  from  a  number  of  narrow  fissures. 

In  1882  S.  F.  Emmons  first  published  the  results  of  his  ex- 
aminations of  the  Leadville  silver-lead  deposits,  in  which  it  was 
shown  that  these  were  entirely  formed  by  metasomatic  replace- 
ment of  the  limestone  by  galena  and  other  minerals.  A  little 
later,  J.  S.  Curtis  published  his  first  results  in  regard  to  the 
silver-lead  deposits  of  Eureka,  Nevada,  in  which  he  arrived  at 
substantially  the  same  results  as  Mr.  Emmons.  Though  these 
deposits,  as  well  as  those  of  Leadville,  are  not  to  be  regarded 
as  fissure-veins,  it  was  evident  that  the  same  process  might  be 
considered  as  active  along  fissures,  provided  the  waters  circu- 
lating in  them  had  the  composition  attributed  to  those  of  Lead- 
ville and  Eureka.  The  results  obtained  were  certainly  of  the 
greatest  interest  to  students  of  fissure-veins,  and  threw  a  new 
light  on  many  obscure  facts.  During  the  following  years,  Mr. 
Emmons,  who  had  visited  a  great  number  of  mining  regions 
in  the  West  containing  fissure-veins,  published  several  papers,! 
in  which  he  maintained  that,  for  a  great  number  of  the  veins 
formerly  considered  as  containing  ore  deposited  in  open  spaces, 
another  and  much  more  plausible  explanation  could  be  advanced, 
namely,  that,  in  many  cases,  the  fissures  had  not  been  opened 
to  any  noteworthy  extent,  but  only  so  much  as  to  admit  the 
passage  of  the  mineral-bearing  waters.  The  latter  had  attacked 
the  rock  on  either  side  of  the  fissure,  and,  by  a  process  of 
metasomatic  replacement,  had  deposited  ores  in  the  place  of 

*  Proc.  Am.  Acad.  Arts  and  Sci.,  vol.  xiii.  (new  series,  vol.  v.),  1878,  pp.  253-309. 
f  The  Comstock  Lode.    New  York,  1879. 

J  "The  Genesis  of  Certain  Ore-Deposits,"  Trans.,  xv.,  125,  1886  ;  "Structural 
Eelationsof  Ore-Deposits,"  Trans.,  xvi.,  804,  1887. 


510  METASOMATIC    PROCESSES   IN    FISSURE-VEINS. 

the  simultaneously  dissolved  rock-constituents.  Applying  this 
process  to  composite  veins,  consisting  of  a  number  of  narrow 
fissures,  and  considering  that  gradual  replacement  had  taken 
place,  extending  into  the  rock  on  each  side  of  each  smaller 
fissure,  Mr.  Emmons  succeeded  in  showing  how,  under  certain 
circumstances,  a  banded  structure  such  as  had  ordinarily  been 
attributed  to  the  filling  of  open  spaces  could  to  some  extent 
result  from  the  process  of  replacement. 

During  the  following  years  the  theory  of  the  formation  of 
fissure-veins  by  replacement  rapidly  gained  ground;  and  for 
some  time  it  seemed  as  if  the  old  view  of  deposition  in  open 
spaces  were  doomed  to  complete  extinction.  Carried  away  with 
the  importance  and  interest  of  the  metasomatic  theory,  many 
geologists  and  mining  engineers  extended  its  teachings  beyond 
proper  bounds,  and  were  prone  to  speak  of  any  fissure-vein  as 
unquestionably  a  product  of  replacement.  Attempts  were  made 
to  show  that  open  fissures  could  not  exist  unsupported,  at  any 
rate  below  the  most  superficial  depths ;  and  facts  and  proofs 
were  too  often  neglected  for  bare  assertions  that  metasomatic 
replacement  had  taken  place.  Posepny,  in  the  discussion  of  his 
paper,*  protested  against  this  unwarranted  extension  of  a  most 
excellent  and  well-founded  theory,  and  stated  with  some  force 
that  the  experience  and  observations  of  a  hundred  years  were 
not  to  be  thrown  away  without  very  careful  scrutiny.  The 
pendulum  had  now  swung  to  its  extreme  position ;  and  it  was 
not  unnatural  that  a  reaction  should  follow.  It  gradually  be- 
came clear  on  the  one  hand  that  open  spaces  can  and  do  exist 
down  to  a  depth  of  many  thousand  feet,t  and  that  these  open 
cavities  may  be  filled  by  the  action  of  mineral-bearing  water. 
On  the  other  hand,  it  is  evident  that  there  is  ample  room  for 
processes  of  replacement  in  fissure-veins,  which  may  either  af- 
fect the  surrounding  country-rock  without  producing  notable 
amounts  of  ore,  or,  on  the  other  hand,  may  attack  it  in  such  a 
way  as  to  convert  it  wholly  or  partially  into  valuable  minerals. 

Some  kind  of  metasomatic  action  is  usually  noticeable  in  the 
rock  adjoining  the  fissure.  But  it  is  not  to  be  denied  that  in 
many  cases  this  alteration  is  very  slight;  and  in  a  few  veins  it 
may  be  entirely  absent. 

*  This  volume,  p.  239.  s 

t  Van  Hise  and  Hoskins.     In  "  Principles  of  Pre-Cambrian  Geology,"  16th 
Ann.  Rept.  U.  S.  Geol.  Sum.,  part  i. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  511 

Calculation  of  Analyses. 

In  order  to  trace  the  metasomatic  changes  by  which  one 
mineral  has  resulted  from  another,  it  is  necessary  to  know  the 
composition  of  each,  and  the  change  in  volume  during  the  al- 
teration. Without  the  latter  the  problem  is  capable  of  many 
solutions,  any  one  of  which  may  be  possible,  though  not  true. 
Only  when  some  definite  data,  such  as  the  constancy  of  one 
constituent,  are  available,  can  the  changes  be  determined  with- 
out reference  to  relative  volumes.  For  instance,  the  percentage- 
composition  and  specific  gravity  of  argentite  and  pyrargyrite 
are  as  follows : 

S  Ag  Sb  Sp.  Gr. 

Per  cent.  Per  cent.  Per  cent. 

Argentite  (Ag2S),       .         .         .13.0  87.0  7.0 

Pyrargyrite  (Ag3SbS3),       . .(.  -'....    18.0  60.0  22  5.8 

Pyrargyrite  may  be  altered  into  argentite ;  but  analyses  alone 
give  no  complete  clue  to  the  character  of  the  alteration.  Sup- 
posing, however,  that  we  have  found  that  1000  cub.  centim.  of 
pyrargyrite  becomes  570  of  argentite;  then  we  may  calculate 
that  about  9  kilos  of  sulphur  and  22  of  antimony  have  been 
removed  from  100  kilos  of  pyrargyrite  during  the  process, 
while  the  silver  has  remained  constant.  Supposing,  again,  that 
we  have  found  pyrargyrite  altered  into  argentite  without  change 
of  volume;  then  from  the  original  100  kilos,  2.24  of  sulphur 
and  22  of  antimony  have  been  lost,  and  44.8  of  silver  added. 

To  exemplify  further  the  many  ways  in  which  even  simple 
metasomatic  problems  can  be  solved,  we  may  take  the  well- 
known  change  of  olivine  to  serpentine,  consisting,  as  ordinarily 
considered,  in  a  simple  hydration  of  the  original  mineral.  And, 
in  order  to  simplify  the  matter  still  further,  we  may  substitute 
for  olivine  the  pure  magnesium  orthosilicate,  occurring  as  a 
mineral  under  the  name  of  forsterite,  and  assume  the  resulting 
serpentine  to  contain  no  iron.  The  formulas  show  that  serpen- 
tine cannot  be  derived  from  olivine  or  forsterite  by  means  of  a 
simple  addition  of  water.  It  may,  however,  be  derived  from 
enstatite  (which  is  a  magnesium  metasilicate)  and  forsterite,  as 
follows : 

Mg2  SiO4  +  Mg  Si03  +  2H2O  =  H;  Mg3  Si2  O9. 

Translated  into  kilograms,  this  means  that  50.8  kilos  of  fors- 
terite +  36.2  of  enstatite  -I- 13  of  water  is  equal  to  100  kilos  of 


512  METASOMATIC   PROCESSES   IN   FISSURE-VEINS. 

serpentine.  This  again  translated  into  volumes  by  aid  of  the 
specific  gravities,  means  that  15.8  cb.  crn.  forsterite  +  ll.Tcb.  cm. 
enstatite  -f  13  cb.  cm.  water  is  equal  to  40  cb.  cm.  serpentine,  or 
that  27.5  cb.  cm.  anhydrous  silicates  are  needed  to  produce 
40  cb.cm.  serpentine.  In  other  words,  the  increase  of  volume 
during  the  process  of  serpentinization  amounts  to  nearly  one- 
half; — the  specific  gravity  of  forsterite  being  3.24,  that  of  en- 
statite, 3.1 ;  and  that  of  serpentine,  2.5. 

Serpentine  may  also  be  obtained  by  adding  silica  and  water 
to  forsterite.  Thus,  3Mg2  Si04  +  4H20  +  Si02  =  2H4  Mg3  Si209. 
Calculating  in  the  same  manner  as  above,  we  find  that  131 
cb.  cm.  of  forsterite  results  in  221  of  serpentine,  which  represents 
an  increase  in  volume  of  somewhat  more  than  two-thirds. 

Still  another  way  of  derivation  is  by  subtracting  MgO  and 
adding  water,  as  shown  by  the  following  formula : 

2Mg2  Si04  +  2H2O=:  H4  Mg3  Si2O9  +  MgO. 

This  again  is  equivalent  to  the  formation  of  110.4  cb.  cm.  of 
serpentine  from  86.3  of  forsterite,  or  an  increase  of  volume  of 
only  a  little  more  than  one-fourth. 

Many  other  formulas  could  be  put  forward,  which  would 
explain  the  formation  of  serpentine,  each  showing  a  difference 
in  the  relation  of  volume  of  the  secondary  mineral  to  that  of 
the  fresh.  Even  in  this  simple  case  it  might  be,  in  any  given 
problem  occurring  in  nature,  extremely  difficult  to  decide  with 
confidence  which  particular  formula  should  be  applied.  The 
problem  only  becomes  definite  when  we  positively  know  the 
relation  of  volume  of  original  substance  to  that  of  secondary 
substance.  It  is  perhaps  superfluous  to  add  that  the  mere 
knowledge  of  specific  gravities  does  not  give  this  relation  of 
volumes. 

When  we  have  to  consider  metasomatic  processes  affecting 
rock-masses,  aggregates  of  from  two  to  six  or  more  minerals, 
the  complexity  of  the  problem  becomes  immensely  greater;  for 
each  of  these  constituent  minerals  may  have  suffered  different 
metasomatic  changes.  Some  may  have  remained  unaltered, 
while  others  have  been  completely  replaced ;  and  others,  again, 
may  have  lost,  or  gained,  or  exchanged  one  or  more  elements. 
To  calculate  the  sum  total  of  these  changes  is  often  an  ex- 
tremely puzzling  task. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  513 

The  mineral  composition  of  the  altered,  as  well  as  the  fresh, 
rock  may  be  accurately  calculated  by  methods  known  to  petro- 
graphy, if  its  analysis,  as  well  as  those  of  the  constituent  min- 
erals, be  available.  Even  where  the  latter  are  only  approxi- 
mately known,  a  fairly  accurate  calculation  may  be  made.  Thus, 
for  instance,  from  an  analysis  of  an  altered  granite  containing 
pyrite,  calcite,  magnesite,  siclerite,  sericite  and  quartz,  the  per- 
centages of  these  minerals  may  be  obtained  with  fair  accuracy. 

The  chemical  changes  suffered  during  any  alteration  of  a 
rock  may  be  considered  by  unit-weight  of  original  substance 
or  by  unit-volume  of  the  same.  The  results  will  be  identical 
if  both  rocks  are  non-porous,  or  if  both  have  the  same  porosity. 
If  the  actual  additions  and  subtractions  should  happen  to  bal- 
ance, then  the  percentage-analyses  offer,  by  comparison,  direct 
evidence  as  to  the  quantitative  alteration.  If,  besides,  during 
the  alteration,  the  porosity  of  the  two  rocks  remain  the  same, 
then  the  changes  measured  by  unit-weight  will  be  identical 
with  those  measured  by  unit-volume.  This  exact  balancing  of 
gains  and  losses,  however,  is,  of  course,  exceedingly  rare.  If 
we  do  not  know  the  relation  of  volumes  between  the  two  rocks, 
other  ways  must  be  sought  for,  at  least,  a  partial  solution  of 
the  problem.  If  we  know  that  one  or  more  new  constituents 
have  been  added,  we  may  subtract  these,  recalculate  on  100, 
and  then  compare  the  analyses.  This  method  in  many  cases 
leads  to  fairly  correct  results ;  but  it  must  be  applied  with  the 
understanding  that,  ordinarily,  it  will  only  give  approximate 
results ;  and  that,  if  there  be  many  partial  additions  and  sub- 
tractions, the  inaccuracies  may  be  very  great,  and  actual  losses 
and  gains  may  appear  reversed. 

If  we  know  that  one  constituent  has  remained  constant,  with 
neither  gain  nor  loss  (as  the  silver  in  the  example  cited  above), 
then  correct  results  may  be  obtained  by  recalculation  on  this 
assumption,  as  has  been  shown.  This  mode  of  calculation  has 
been  used  by  Scheerer,  J.  Roth,  and  lately  also  by  Prof.  G-.  P. 
Merrill,  in  his  book  on  "  Rocks  and  Rock- Weathering."  It  is 
only  rarely,  however,  that  we  are  able  to  recognize  this  con- 
stancy ;  for  nearly  all  constituents  undergo  some  change  in  the 
alterations  of  wall-rocks.  Even  alumina,  often  considered  to 
be  nearly  insoluble,  shows  great  changes  in  some  altered  rocks. 
Besides,  if  we  base  recalculation  on  some  compound  of  which 


514  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

but  a  small  percentage  is  present,  the  multiplication  of  errors 
may  play  havoc  with  the  .result.  Altogether,  this  mode  of 
ascertaining  gains  and  losses  must  be  applied  with  the  greatest 
caution. 

Any  given  analysis  of  fresh  and  altered  rock  may  correspond 
to  several  very  different  mineral  compositions.  For  any  given 
mineral  composition,  the  constancy  of  one  constituent  during 
the  change  to  another  (also  known)  mineral  composition,  de- 
termines the  change  in  volume  involved  (not  considering  po- 
rosity). When  the  change  in  volume  can  be  directly  ascer- 
tained, we  are  definitely  able  to  obtain  the  absolute  gains  and 
losses  suffered  by  unit-volume  of  the  rock;  and  this  comparison 
is  ordinarily  the  one  which  throws  most  light  on  the  processes 
involved.  But  relations  of  volume  are  difficult  to  obtain  with 
certainty,  especially  in  regard  to  a  rock  made  up  of  a  number 
of  minerals  which  have  suffered  different  changes.  As  a  rule, 
in  fissure-veins,  the  replacing  minerals  are  denser  than  those 
replaced;  so  that,  if  the  rock  remained  compact,  there  would 
be  a  decrease  in  volume.  But  as  there  usually  are  no  indica- 
tions of  compressive  stress  in  the  altered  rock,  the  result  of 
this  replacement  of  lighter  by  heavier  minerals  will  be  a  po- 
rosity expressed  by  a  notable  difference  in  the  experimentally 
determined  specific  gravity  of  the  rock  and  that  calculated  from 
its  known  mineralogical  composition.  This  may,  in  some  cases 
at  least,  justify  the  assumption  that  the  rock  has  not  changed 
its  volume  as  a  whole ;  and  if  this  be  true,  a  direct  comparison 
between  equal  volumes  of  fresh  and  porous  altered  rock  is 
practicable.  Should  it  appear  probable  that  an  actual  change 
of  volume  has  taken  place,  either  by  expansion  or  contraction, 
it  will  ordinarily  be  a  difficult  matter  in  each  case  to  ascertain 
the  exact  amount  of  this  change,  without  which  knowledge  the 
calculations  cannot  be  carried  out.  If  there  is  porosity,  the 
changes  by  unit-weight  of  original  substance  may  differ  greatly 
from  those  obtained  by  unit-volume;  hence  porosity  is  a  factor 
which  must  not  be  overlooked.  One  method  may  indeed  indi- 
cate the  very  opposite  of  the  other.  For  instance,  by  the  first 
way,  it  may  be  ascertained  that  a  rock  has  gained  several  per 
cent,  of  its  weight;  while  the  other  method  may  show  that 
an  actual  loss  per  unit-volume  of  original  rock  has  taken 
place. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  515 

In  the  considerations  outlined  above,  it  is  assumed  that  the 
rocks  to  be  compared  have  undergone  no  change  of  volume 
since  their  removal  from  the  surrounding  mass.  In  regard  to 
the  fresh  rocks,  there  is,  as  a  rule,  little  fear  of  this.  Certain 
altered  rocks,  however,  easily  soften  or  crumble  when  exposed 
to  the  air,  probably  indicating  that  an  increase  in  volume  is 
taking  place.  An  exceedingly  slight  action  of  this  kind  would 
evidently  be  sufficient  to  break  up  the  rock  if  it  were  not  con- 
fined. There  is,  therefore,  little  reason  to  fear  that  such 
change  of  volume  has  taken  place,  if  the  specimens  of  altered 
rock  remain  firm  and  solid. 

Criteria  of  Metasomatism. 

Considerable  space  was  devoted  to  this  subject  in  the  dis- 
cussion of  Posepny's  paper  in  the  Transactions  of  the  Insti- 
tute,* and  it  may  therefore  be  passed  with  brief  notice. 

It  is  not  always  easy  to  be  sure  whether  metasomatic  action 
really  has  taken  place,  and  in  deciding  this  question  the  great- 
est caution  must  be  observed.  The  mere  occurrence  of  two 
minerals  together  by  no  means  proves  that  one  has  been  de- 
rived from  the  other.  The  chief  difficulty  is  to  draw  the  dis- 
tinction between  molecular  processes  involving  simultaneous 
dissolution  and  precipitation,  on  the  one  hand,  and  previous 
dissolution  and  subsequent  precipitation  on  the  other. 

The  only  decisive  criterion  is  that  of  metasomatic  pseudo- 
morphism, involving  the  proof  (generally  to  be  furnished  by 
microscopic  study)  as  to  whether  simultaneous  dissolution  and 
deposition  have  actually  taken  place.  The  most  satisfactory 
proof  is  the  distinct  alteration  of  well-defined  crystals  (or,  at 
least,  well-defined  grains)  of  the  original  mineral  into  the  sec- 
ondary mineral,  in  such  a  way  that  the  latter  projects  into  the 
former  in  prisms  or  fibers,  having  crystalline  outlines.  Another 
proof  is  afforded  by  sharply  defined  crystals  of  the  secondary, 
embedded  in  the  primary  mineral,  without  any  break  between 
their  surfaces;  but  in  this  case  it  must  be  clear  that  the  re- 
placing mineral  is  really  secondary,  and  was  not  formed  before 
the  primary.  Another  satisfactory  proof  is  given  when,  for 
instance,  in  a  sandstone,  the  newly  formed  mineral  has  in  part 

*  This  volume,  p.  188. 
33 


516  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

a  crystalline  form,  and  its  surfaces  squarely  intersect  the  grains 
of  clastic  material  which  it  partly  replaces. 

There  are  many  other  available  criteria  such  as  the  enlarge- 
ment of  fissures  in  the  replaced  mass.  An  instance  is  shown 
in  Fig.  30,  representing  a  veinlet  of  quartz  formed  by  filling  a 
small  open  fissure,  and  adjoined  on  one  side  by  galena,  which 
extends  most  irregularly  into  the  adjoining  quartzite.  (See 
also  Fig.  28*.)  The  retention  of  the  structure  of  the  original 
mass  by  the  secondary  replacing  minerals  is  also  an  excellent 
criterion,  provided  it  be  identified  beyond  doubt.  Thus,  for 
example,  certain  porphyritic  rocks  have  suffered  nearly  com- 
plete silicification,  but  preserve  almost  entirely  the  outlines  of 
phenocrysts  and  the  structure  of  the  ground-mass.  The  occur- 
rence of  remaining  nuclei  of  unaltered  rock  is  sometimes  an 
available  criterion ;  but  it  must  be  used  with  caution,  and 
probably  has  given  rise  to  misinterpretations,  on  account  of 
its  similarity  to  actual  inclusions  of  country-rock  in  vein-filling. 
In  cases  of  replacement  by  sulphides,  the  unaltered  residual 
rock  may  be  sharply  defined,  and  may  closely  simulate  inclu- 
sion. In  cases  of  replacement  by  calcite  or  quartz,  there  is 
less  of  this  danger,  as  the  action  is  usually  more  gradual.  If 
the  alteration  or  replacement  proceeds  normally  from  the  out- 
side of  a  crystal  or  angular  mass  of  rock,  the  tendency  will  be 
towards  rounded  residual  portions  in  the  interior  of  the  mass, 
as  may  often  be  seen  in  altered  crystals  of  olivine.  This 
criterion  for  replacement,  suggested  by  Gr.  F.  Becker,  may 
under  circumstances  prove  useful.  Generally,  however,  the  re- 
placement proceeds  very  irregularly,  owing  to  the  effect  of 
little  cracks  and  fissures.  Slight  clay-seams  may  often  inter- 
pose an  absolute  barrier,  so  that  sharp  contacts  of  replaced  and 
fresh  rocks  result.  The  replacement  of  crystals  or  angular 
fragments  may  occur  without  changing  in  the  least,  even  by 
the  rounding  of  corners,  the  form  of  the  masses. 

In  conclusion,  I  would  repeat  and  adopt  the  statement  of 
Mr.  Becker,f  that  "  the  theory  of  the  substitution  of  ore  for 
rock  is  to  be  accepted  only  when  there  is  definite  evidence 
of  pseudomorphic,  molecular  replacement." 

*  A  somewhat  similar  and  excellent  illustration  is  given  in  Rickard's  "  Vein- 
Walls,"  Trans.,  xxvi.,  195,  from  the  Hillside  mine,  Arizona, 
f  Discussion  of  Posepny's  paper,  this  volume,  p.  204. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  517' 

In  many  fissure-veins,  practically  all  of  the  economically  im- 
portant ore  has  been  formed  by  replacement ;  and  for  these 
deposits  the  term  replacement-veins  is  especially  used.  But  if 
we  do  not  confine  ourselves  to  the  fluctuating  definition  of 
"  pay-ore,"  practically  all  fissure-veins  are,  to  some  extent  at 
least,  replacement-veins. 

Mr.  Emmons*  has  suggested  the  following  criteria  for  "  re- 
placement-veins "  in  the  narrower  sense  of  the  word :  (1)  absence 
of  symmetrical  banding  or  comb-structure  in  the  vein-material, 
and  of  breccias  of  country-rock,  cemented  by  vein-material ;  (2) 
great  irregularity  in  the  width  of  the  ore-bodies,  which  may 
reach  very  great  dimensions;  (3)  general  lack  of  definition 
between  ore-body  and  wall-rock. 

Crystallization  of  Secondary  Minerals  in  Other  Bodies. 

It  has  been  known  for  a  long  time  that  perfect  crystals  of 
minerals,  such  as  quartz,  for  instance,  may  be  formed  in  soft 
rocks  such  as  shale,  limestone,  clay,  etc. ;  but  concerning  their 
exact  mode  of  formation  there  has  been  considerable  difference 
of  opinion.  Probably  the  prevailing  view,  some  20  years  ago, 
was  that  the  growing  crystal  had,  by  means  of  its  force  of 
crystallization,  pushed  apart  the  surrounding  mass.  This  was 
indeed  the  opinion  of  von  Groddeck,  who  declaresf  that  the 
formation  of  a  completely  developed  crystal  in  a  solid,  rigid 
mass  is  not  possible.  Apparent  exceptions,  such  as  magnetite 
in  chloritic  schists,  he  considers  as  caused  by  development, 
while  the  rock  was  soft,  under  the  influence  of  metamorphic 
agencies.  There  is  no  doubt  good  foundation  for  this  view; 
for  in  magmas  and  solutions  crystals  may  grow  to  perfect  de- 
velopment, and  if,  for  instance,  a  saturated  solution  of  ferrous 
sulphate  is  mixed  with  some  neutral  fine  powder  to  a  soft  pulp, 
extremely  clear  and  sharply  developed  crystals  of  this  salt  will 
separate  out. 

But  it  has  gradually  become  apparent  that  it. is  not  necessary 
to  assume  complete  permeation  and  softening  of  a  rock  by 
concentrated  solutions,  in  order  to  account  for  secondarily- 
developed  crystals.  It  is  now  well  known  that  the  secondary 
development  of  crystals  in  solid  material  is  not  only  a  possible 

*   U.  S.  Geol  Surv.,  Folio  38,  on  Butte,  Montana. 

f  Die  Lehre  von  den  Lagerstatten  der  Erze,  Leipzig,  1879,  p.  68. 


518  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

but  an  exceedingly  common  phenomenon,  and  that  it  may  be 
caused  by  simple  metasomatic  replacement  of  the  surrounding 
material. 

The  mechanical  force  of  crystallization  probably  co-operates, 
to  some  extent,  with  the  chemical  agencies  of 'replacement; 
and  when  the  surrounding  mass  is  thoroughly  softened  and 
saturated  by  the  depositing  solutions,  the  former  force  may  be 
alone  active.  The  growing  crystal  may  include  parts  of  the 
surrounding  rock,  as  is  seen  in  Figs.  3  and  4,  representing  cal- 
cite  in  quartz,  and  in  Fig.  27,  showing  inclusions  of  sericite  in 
pyrite.  This  is  analogous  to,  but  not  identical  with,  the  occur- 
rence of  inclusions  of  fluid  and  glass  in  crystals  separating  out 
from  solutions  or  magmas.  It  is  not  uncommon  to  find  new 
crystals  of  perfect  development  generated  in  a  grain  of  another 
substance,  such  as  quartz  or  feldspar,  without  any  disturbance 
of  the  optical  orientation  of  the  older  minerals,  such  as  unfail- 
ingly would  occur  were  the  process  simply  one  of  mechanical 
force.  No  doubt  the  exchange  of  substance  takes  place 
through  the  medium  of  a  film  of  water,  but  this  is  generally 
so  exceedingly  thin  that  the  strongest  powers  of  the  micro- 
scope fail  to  reveal  it.  In  many  cases,  however,  the  new  min- 
eral begins  to  grow  on  the  planes  of  small  fractures,  traversing 
the  original  mineral.  Fluid  inclusions  accumulate  on  this 
plane  ;  and  the  first  separation  of  the  new  mineral  appears  as 
little  dots,  closely  connected  with  the  inclusions.  No  doubt 
the  line  between  metasomatism  and  cavities  of  dissolution  sub- 
'  sequently  filled  is  a  very  fine  one,  and  difficult  to  draw  in  many 
cases ;  but  when  intermediate  cavities  or  subsequent  fillings 
cannot  be  traced  with  the  microscope,  the  process  may  be 
classed  as  metasomatic;  and  in  the  great  majority  of  cases  this 
interpretation  will  be  correct. 

Secondary  Alteration  of  Veins. 

Under  any  given  conditions,  minerals  tend  to  assume  the 
forms  most  stable  under  those  conditions.  Since  the  conditions 
prevailing  during  vein-formation  are  very  different  from  those 
prevailing  afterwards,  it  may  be  inferred  that  the  products  of 
the  first  process  might  easily  be  changed.  Such  is  indeed  the 
case.  We  find  many  altered  rocks  which  have  evidently  under- 
gone more  than  one  change.  Especially  near  the  surface, 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  519 

under  the  influence  of  oxidizing  waters,  the  minerals  formed  in 
the  rocks  along  veins  are  apt  to  suffer  great  changes.  Exam- 
ples are  frequent,  showing  that  the  minerals  which  filled  the 
open  spaces  along  a  vein  have  been  completely  dissolved  and 
partly  or  wholly  replaced  by  others.  This  is  particularly  true 
of  fillings  of  calcite  or  barite.  Many  instances  are  known  in 
which  large  masses  of  these  minerals  have  been  completely  dis- 
solved and  replaced  by  quartz.  Such  are  the  well-known  de- 
posits of  Schneeberg  in  Saxony,  and  those  of  the  De  Lamar 
mine  in  Owyhee  county,  Idaho. 

Structure  and  Composition  of  Metasomatic  Vein-Rocks  and  their 
Relation  to  General  Metamorphism. 

The  aggregates  replacing  the  original  wall-rocks  of  veins 
show  great  variety  of  structure.  It  is  most  common,  perhaps, 
that  the  structure  of  the  resulting  rock  is  much  finer  than  that 
of  the  primary.  As  examples  may  be  cited  silicification,  which 
nearly  always  results  in  micro  crystalline  and  cryptocrystalline 
aggregates,  and-  sericitization,  which  generally  results  in  a  mass 
of  very  fine  tufted  fibers.  This  is  not,  however,  a  general  rule ; 
because  certain  easily  soluble  minerals,  when  replacing  others, 
produce  a  much  coarser  aggregate  than  that  of  the  original 
rock.  Of  such  character,  for  instance,  are  the  carbonates. 
(See  Fig.  27.)  Fluorite  replacing  limestone  (see  Fig.  14)  is  an- 
other instance  of  coarser  grain  shown  by  the  secondary  rock. 

As  a  general  rule,  the  resulting  minerals  have,  on  the  whole, 
a  greater  aggregate  specific  gravity  than  the  original  minerals. 
Muscovite,  sericite,  fluorite,  the  different  carbonates,  pyrite  and 
other  sulphides  (as  well  as  topaz  and  tourmaline,  so  abundantly 
formed  in  tin-deposits)  are  instances.  On  the  other  hand,  there 
are  exceptions,  such  as  the  development  of  jasperoids  and  other 
quartzose  rocks  from  limestone,  in  which  case  the  resulting 
material  has  less  specific  gravity  than  the  original. 

A  banded  structure  of  the  altered  rock  may  possibly,  as  men- 
tioned above  (p.  590),  result  from  replacement  by  sulphides  in  a 
sheared  rock,  in  which  the  shear-planes  are  closely  spaced ;  but 
this  banding  is  not  likely  to  be  as  well  marked  as  the  crustifi- 
cation  often  caused  by  the  gradual  filling  of  open  spaces.  From 
these  two  sorts  of  banding  a  third  must  be  differentiated, 
namely,  the  typical  "  ribbon-structure  "  caused  by  shearing  of 


520  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

the  already-formed  vein,  in  connection  with  which  a  secondary 
concentration  of  gold  and  sulphides  may  have  taken  place  on 
the  shear-planes — whence  the  richness  of  vein-material  often 
associated  with  this  structure. 

In  no  case,  thus  far,  has  any  law  of  progressive  alteration  of 
the  country-rock  of  a  vein  been  detected,  which  would  enable 
us  to  say  that  the  intensity  of  the  process  either  increases  or 
decreases  from  the  surface  down.  Nor  has  any  instance  been 
shown  in  which  the  processes  of  alteration  permanently  change 
with  increasing  depth.  This  does  not  exclude  the  fact  that  oc- 
casionally a  different  subordinate  process  of  alteration  may  be 
introduced.  It  is  known,  for  instance,  that  certain  parts  of  the 
rock  near  the  vein  may  be  locally  silicified,  although  the  prin- 
cipal and  prevailing  process  in  depth,  as  well  as  near  the  sur- 
face, is  of  a  totally  different  character.  Thus,  silicification  and 
the  formation  of  greisen  may  occur  side  by  side  in  cassiterite 
veins,  and  silicification  and  carbonatization  in  cinnabar  veins. 

The  metasomatic  processes  in  wall-rocks  of  fissure-veins  differ 
generally  from  those  of  regional  (static  and  dynamic)  metamor- 
phism.  In  most  cases  oxides  of  iron  and  manganese  such  as 
magnetite,  hematite,  ilmenite  and  pyrolusite,  are  absent  as  a 
primary  development;  and  many  silicates,  exceedingly  com- 
mon in  static  and  dynamic  metamorphism  are,  as  a  rule,  miss- 
ing in  veins.  Among  these  are  amphibole,  biotite,  garnet,  cor- 
dierite,  serpentine,  ottrelite,  and  zoisite.  Chlorite  and  epidote 
are  confined  to  the  vicinity  of  only  one  or  two  classes  of  veins. 
Albite,  exceedingly  common  in  regional  metamorphism,  is  not 
known  as  a  metasomatic  development  in  veins,  though,  like 
orthoclase,  it  may  occur  in  the  filling  of  open  cavities.  Mus- 
covite, calcite,  quartz  and  pyrite  are  common  to  both  kinds  of 
metamorphism.  As  compared  with  the  products  of  contact- 
metamorphism,  we  note  in  metasomatic  vein-phenomena  a 
total  absence  of  the  pyroxenes,  wollastonite,  staurolite,  cyanite, 
andalusite,  vesuvianite  and  garnet.  Only  two  classes  of  veins 
are  characterized  by  tourmaline,  which  is  a  frequently  occurring 
contact-mineral.  Again,  as  compared  with  the  results  of  ordi- 
nary hydro-metamorphism,  we  note  in  the  results  of  metaso- 
matic vein-action  the  scarcity  of  amphibole  as  well  as  of  zeo- 
lites, except  in  one  or  two  classes  of  veins,  and  also  the  rela- 
tively slight  importance  of  chlorite  and  epidote. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  521 

The  degree  of  hydration  in  altered  vein-rocks  is  very  mod- 
erate ;  and  in  some  cases,  as,  for  instance,  in  the  change  of  ser- 
pentine to  magnesite,  there  is  a  distinct  dehydration.  Strongly 
hydrous  minerals  are  not  common  on  fissure-veins. 

I  have  emphasized  these  differences,  to  show  that  the  meta- 
somatic  processes  in  veins  cannot  simply  be  identified  with 
those  that  were  active  in  the  other  phases  of  metasomatism 
mentioned.  In  the  majority  of  cases,  the  vein-processes  have  a 
distinctive  character  of  their  own. 

PART  II. 

MINERALS  DEVELOPED  BY  METASOMATIC  PROCESSES  IN  FISSURE- 
VEINS. 

Quartz  (including  Chalcedonite  and  Opal). — Though  silicic  acid 
is  weak,  and  cannot  under  ordinary  circumstances  expel  even 
carbonic  acid  from  its  compounds,  it  is  easily  deposited  instead 
of  other  minerals,  which  are  dissolved  by  more  active  reagents 
contained  in  the  same  waters.  Hence  the  frequency  of  quartz 
in  the  forms  of  other  minerals.  It  would  be  erroneous  to  say, 
however,  that  silicification  is  a  very  common  metasomatic  pro- 
cess, even  in  veins  containing  quartz  as  a  filling ;  and  very  rarely 
is  it  the  exclusive  process  in  any  given  vein.  It  is  most  common 
in  limestone  and  other  easily  soluble  rocks;  also  in  such  por- 
ous rocks  as  sandstones,  though  here  it  is  usually  to  be  regarded 
rather  as  cementation.  In  rocks  rich  in  silica,  such  as  rhyolite 
or  quartzite,  the  tendency  to  silicification  (probably  by  reason  of 
mass-action)  is  greater  than  in  more  basic  rocks  in  the  same 
district. 

Quartz  replacing  limestone  along  fissures  is  a  common  oc- 
currence. The  process  usually  results  in  a  microcrystalline  or 
cryptocrystalline  aggregate  of  interlocking  grains,  preserving 
the  original  structure,  as  shown  in  Fig.  1,*  which  represents  a 
silicified  limestone  from  the  Diadem  lode,  Plumas  county,  CaL, 
and  shows  the  remaining  outline  of  a  foraminiferal  test.  The 
development  of  the  quartz  is  shown  in  Figs.  3  and  4,f  represent- 

*  After  H.  W.  Turner,  Journal  of  Geology,  vol.  vii.,  No.  4. 
t  The  accompanying  figures,  with  some  exceptions  noted  in  the  list,  were  drawn 
by  myself  under  the  microscope,  with  camera  lucida. 


522  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

ing  rocks  from  Aspen,  Colorado.*  Small  secondary  grains  or 
well-developed  crystals  appear  in  the  limestones  and,  gradually 
extending,  finally  produce  an  aggregate  which,  in  this  case,  is 
somewhat  coarser  than  in  the  rock  from  California.  Quartz 
crystals  with  double  terminals  may  occur  in  metasomatic  rocks, 
but  are  foreign  to  quartz,  filling  open  cavities.  Opal  and  chal- 
cedonite  may  occasionally  also  be  present.  The  resulting  fine- 
grained rocks,  often  stained  brown  or  red,  may,  according  to 
Mr.  Spurr's  proposal,  be  called  jasperoids. 

Daubree  describes  heavy  quartz  veins,  cutting  through  gran- 
ite and  overlying  sedimentary  rocks,  in  the  Central  Plateau 
of  France. f  Besides  quartz,  these  veins  carry  fluorite,  barite, 
calcite  and  galena.  Agate  and  jasper  in  banded  form  are 
also  frequently  present.  From  the  same  description, J  it 
appears  that  in  some  places,  where  these  veins  traverse  lime- 
stone (Muschelkalk),  there  has  been  a  very  strong  silicification 
of  the  enclosing  rock,  as  is  proved  by  means  of  the  occur- 
rence of  crinoids  in  the  compact  quartz  now  forming  part 
of  the  lode.  Another  locality,  also  in  the  Yosges,  is  men- 
tioned as  showing  a  large  deposit  of  fine-grained  hornstone- 
like  quartz,  also  containing  barite  and  fluor-spar,  and  full  of 
little  geodes  with  projecting  crystals  of  quartz.  In  this  sili- 
ceous rock,  silicified  shells  of  avicula  and  pecten  have  been 
found,  showing  its  derivation  from  the  surrounding  lime- 
stone. The  chemistry  of  the  process  is  apparently  simple : 
waters  containing  carbon  dioxide  and  silica  deposit  the  latter, 
while  simultaneously  dissolving  a  corresponding  proportion  of 
calcite. 

In  contrast  to  the  fine-grained  structure  of  jasperoids,  quartz 
deposited  in  open  spaces  is  usually  characterized  by  coarse 
grains,  the  majority  of  which  show  partly  developed  crystal- 
faces.  Crystals  developed  at  both  terminals  do  not  appear, 
though  earlier-developed  individuals,  growing  from  some  de- 
posit, are  surrounded  by  later-developed  grains.  Fig.  2,  which 
shows  the  normal  structure  of  the  quartz  in  the  California  gold- 
veins,  illustrates  this  occurrence. 

*  The  thin  sections  from  which  these  figures  were  made  were  kindly  loaned  to 
me  by  Mr.  J.  E.  Spurr. 

f  Daubree,  Les  Eaux  Souterraines  aux  Epoques  Ardennes,  p.  124. 
J  Loc.  tit.,  p.  151. 


METASOMATIC    PROCESSES   IN   FISSURE-VEINS.  523 

Quartz  may  further  replace  orthoclase,  as  shown  in  Fig.  5, 
with  preservation  of  the  crystal-form.  The  ordinary  course 
of  alteration  of  the  latter  mineral  is  to  quartz,  sericite,  or  kao- 
linite,  and  potassic  carbonate.  In  complete  replacement  by 
quartz,  the  alumina  and  potassa  have  been  carried  away,  and 
the  quartz  has  received  a  considerable  addition.  The  process 
may  also  be  explained  as  a  complete  replacement,  by  means  of 
which  the  orthoclase,  as  such,  has  been  removed,  and  quartz  has 
been  deposited.  In  the  same  manner,  soda-lime  feldspars  may 
be  replaced  by  quartz,  as  well  in  phenocrysts  as  in  the  ground- 
mass.  Even  the  ferromagnesian  silicates  may  suffer  a  similar 
change.  A  partial  replacement  of  hornblende  by  quartz  and 
chlorite  (Fig.  6)  is  common.  The  ground-mass  surrounding 
crystals  of  quartz  in  certain  rhyolites  (Silver  City  and  De  Lamar, 
Idaho)  may  be  replaced  by  quartz,  forming  a  secondary  aureole 
around  the  primary  crystal. 

Under  favorable  and  very  exceptional  circumstances,  veinlets 
containing  coarser  quartz,  simulating  comb-quartz  in  structure, 
may  be  formed  by  replacement.  Fig.  7  represents  a  contact 
between  chloritic  basalt  and  silicified  rhyolite,  on  which  a  small 
quartz  vein  is  developing,  the  crystals  replacing  the  ground- 
mass  of  the  silicified  rhyolite.*  Replacement  of  minerals  by 
chalcedonite  and  opal  instead  of  by  quartz  is  less  common. 
Near  cinnabar  veins,  in  California  and  elsewhere,  serpentine, 
transformed  into  opal,  with  retention  of  the  primary  structure, 
has  been  observed. 

Rutile  and  Anatase. — These  minerals  are  common  in  meta- 
somatic  vein-rocks,  as  secondary  products  after  ilmenite,  titan- 
ite,  titaniferous  magnetite,  biotite,  etc.  Rutile  occurs  in  nearly 
every  altered  titaniferous  rock ;  anatase  (octahedrite)  has  been 
found  in  the  altered  rocks  of  Freiberg  (Stelzner),  Nagyag  (Koll- 
beck),  Schwarzwald  (Sandberger),  and  Silver  Cliff  (Cross). 
Neither  titanite  nor  ilmenite  appear  to  be  stable  under  the  in- 
fluence of  vein-forming  solutions.  In  several  publicationsf  I 
have  assumed  that  the  milky  white  flocculent  mass  (leucoxene) 
which  often  results  in  vein-rocks  from  the  alteration  of  titan- 
iferous minerals  is  titanite ;  but  this  assumption  now  appears  to 

*  20th  Ann.  Eept.  U.  S.  Geol.  Surv.,  part  iii.,  p.  186. 

f  14th  Ann.  Eept.  U.  S.  Geol.  Surv.,  part  ii.,  p.  276,  et  seq.  17th  Ann.  Eept. 
U.  S.  Geol.  Surv.,  part  ii.,  p.  149,  etseq. 


524  METASOMATIC    PROCESSES    IN   FISSURE-VEINS. 

be  incorrect.  The  substance  is  certainly  free  titanic  acid,  as 
shown  by  the  fact  that  no  titanium  is  extracted  by  hydrochloric 
acid,  while  the  mineral  is  attacked  by  boiling  sulphuric  acid. 

Fluorite. — This  mineral  may  replace  many  others.  It  has  gen- 
erally a  purplish,  unevenly  distributed  color,  and  shows  under  all 
circumstances  a  strong  tendency  to  crystal-development.  Its 
formation  from  limestone  is  illustrated  in  Fig.  14,  which  repre- 
sents the  contact  of  one  of  the  many  small  nodules  of  fluorite 
scattered  in  a  limestone  breccia  from  a  mine  in  the  Judith 
mountains,  in  Montana.*  The  sharp  angles  of  the  cube  will 
be  seen  projecting  into  the  limestone;  the  latter  contains 
many  imperfect  fossil  shells,  and  some  crystals  of  secondary 
quartz. 

While  the  reaction  involved  in  this  process  is  not  clearly  es- 
tablished, it  is  probably  a  complete  replacement,  the  more  solu- 
ble calcite  being  taken  up  by  the  waters  and  the  less  soluble 
fluorite  simultaneously  deposited. 

Fluorite,  together  with  quartz  and  pyrite,  is  further  formed 
as  a  replacement-product  of  orthoclase,  as  shown  in  Fig.  10, 
representing  a  feldspar  grain  from  a  breccia  in  the  Independence 
mine,  Cripple  Creek,  Colo.  The  replacement  of  some  of  the 
phonolite  and  fine-grained  granite-andesite  breccia  from  Crip- 
ple Creek  has  resulted  in  a  large  quantity  of  crystalline  fluorite 
and  quartz  (Fig.  9).  Wherever  calcium  silicates  are  present, 
and  the  waters  contain  sodic  fluoride,  the  result  will  be  sodic 
silicate  and  calcic  fluoride.  In  this  way  the  mineral  may  be 
formed  by  interchange  of  constituents,  f  Alkaline  fluorides 
and  calcic  fluorides  may  exist  together  in  the  same  solution; 
but  alkaline  carbonates  decompose  fluorite,  yielding  alkaline 
fluorides  and  calcic  carbonate ;  hence  fluorite  cannot  exist  as 
such  in  waters  containing  alkaline  carbonates. 

Calcite. — This  mineral  and  the  allied  magnesian  and  ferrous 
carbonates  are  exceedingly  common  in  metasomatic  vein-rocks, 
and  their  occurrence  gives  testimony  of  the  energetic  altering 
action  of  carbon  dioxide  and  alkaline  carbonates  on  nearly  all 
silicates.  The  metasomatic  calcite  is  of  fine  or  coarse  grain — 
the  latter  especially  when  replacing  easily  soluble  minerals.  It 

*  This  section  was  prepared  for  Mr.  W.  H.  Weed,  who  kindly  allowed  me  to 
use  it.  t  Bischof,  Chem.  *Geol,  Bonn,  1864,  ii.,  p.  95. 


METASOMATIC    PROCESSES   IN   FISSURE-VEINS.  525 

has  very  little  tendency  to  crystallize,  nearly  always  occurring 
in  irregular  grains. 

Calcite  replaces  quartz  to  a  greater  or  less  extent,  though  in 
rocks  containing  also  silicates  like  feldspars  and  hornblende, 
these  minerals  are  first  attacked,  and  the  replacement  of  the 
quartz  is  usually  only  partial.  The  quartz  is  evidently  dis- 
solved by  waters  containing  alkaline  carbonates,  and  a  corre- 
sponding quantity  of  calcic  carbonate,  also  dissolved  in  the 
water,  is  deposited  in  its  place.  Under  ordinary  pressure  and 
temperature,  water  does  not  dissolve  quartz ;  but  increase  of 
either  results  in  solution  to  some  extent.  The  presence  of  car- 
bon dioxide  alone  does  not  promote  the  solubility.  No  pseudo- 
morphs  of  calcite  after  quartz  are  known — an  evidence  of  the 
resistance  of  the  latter  mineral  to  solution. 

The  replacement  of  quartz  by  calcite  in  granitic  rocks  is  shown 
in  Figs.  13  and  15.  The  calcite,  developed  along  cracks  and 
fissures,  spreads  and  corrodes  the  original  substance.  Small 
masses  of  sometimes  rhombohedral  calcite  project  into  the 
quartz.  Rounded  and  isolated  bodies  of  calcite  may  also  form 
on  inclined  fracture-planes;  by  extension  they  finally  join  and 
form  larger  masses. 

Orthoclase  is  likewise  replaced  by  calcite  in  many  granitic 
rocks  adjoining  veins.  The  process  is  similar  to  the  replace- 
ment of  quartz ;  but  the  feldspars  are  much  more  easily  soluble 
than  quartz.  Chemically,  the  process,  as  already  pointed  out 
by  Bischof,*  may  be  considered  as  simply  due  to  the  attack  of 
waters  containing  calcic  bicarbonate.  The  carbon  dioxide  of 
the  latter  alters  the  orthoclase ;  the  resulting  alkaline  carbon- 
ates and  silica  are  carried  away ;  just  in  what  form  the  alumina 
is  removed  is  not  certain.  In  the  majority  of  cases  a  simulta- 
neous formation  of  sericite  occurs ;  so  that  the  actual  loss  of 
A1203  may  be  very  small.  Even  more  easily  effected  is  the  re- 
placement of  soda-lime  feldspars  by  calcite ;  for  here  the  orig- 
inal mineral  contains  one  of  the  constituents  of  the  result.  As 
is  well  known,  andesine,  labradorite  and  anorthite  may  be 
partly  converted  into  calcite  under  the  influence  of  ordinary  cold 
waters  containing  carbon  dioxide. 

In  the  same  manner,  it  is  common  to  find  pyroxene,  amphi- 

*  Chem.  GeoL,  ii.,  p.  428. 


526  METASOMATIC    PROCESSES   IN   FISSURE-VEINS. 

bole  and  biotite  partly  converted  into  calcite.  In  vein-forming 
processes,  these  are  usually  the  first  minerals  to  suffer  from 
the  attack.  The  magnesia,  alumina  and  ferrous  oxide  usually 
remain  in  the  form  of  chlorite  or  other  secondary  silicates, 
though  some  of  the  magnesia  and  iron  may  also  form  car- 
bonates. 

Magnesite  and  Dolomite. — Small  quantities  of  magnesian  and 
ferrous  carbonates  nearly  always  combine  with  the  newly 
formed  calcite,  but  in  many  cases  are  of  no  special  importance. 

A  change  of  limestone  to  magnesite  is  not  known  as  a  vein- 
forming  process.  Dolomitization  commonly  occurs,  however, 
in  limestones  adjoining  fissure-veins,  as,  for  instance,  described 
by  Spurr*  at  Aspen,  Colorado.  At  this  place,  as  the  dolomit- 
ization  proceeds  irregularly  from  the  fissures,  the  coarse  calcite 
grains  are  broken  up  into  smaller  rhombohedral  crystals,  of 
the  yellowish  tinge  characteristic  of  dolomite.  The  process  is 
clearly  one  of  metasomatic  replacement,  carried  on  by  waters 
containing  magnesic  bicarbonate,  or  even  chloride.  The  cor- 
rectness of  this  view  has  been  shown  by  synthetical  experi- 
ments, f 

Mr.  Spurr  shows  convincingly  that  ordinary  circulating  sur- 
face-waters do  not  dolomitize  the  limestone  which  they  traverse. 
The  reagents  which  produced  this  dolomitization  must  have 
been  more  potent.  Several  hot  springs  in  the  vicinity  of  Aspen, 
Colorado,  carry  carbonates  of  lime  and  magnesia,  and  also  a 
large  amount  of  sodium  chloride  and  magnesium  chloride. 
These  waters,  as  shown  by  analyses,  have  a  distinct  dolomitiz- 
ing  influence  on  the  adjoining  limestone.  The  change  is  also 
accompanied  by  silicification  and  ferration. 

Dolomitic  carbonates  may  also  partly  replace  albite,  as  shown 
by  Mr.  H.  "W.  TurnerJ  in  the  case  of  a  mineralized  dike  of 
albite  rock  from  Tuolumne  county,  Cal.  An  accompanying  al- 
most pure  magnesite  may  possibly  have  resulted  from  the  altera- 
tion of  the  adjoining  serpentine. 

Magnesite  and  dolomitic  carbonates  are  very  apt  to  form  from 
serpentine,  as  illustrated  in  the  country-rock  adjoining  the  Idaho 
vein,  Grass  Valley,  Cal.§  The  fine-grained  serpentine  is  trans- 

*  Monograph  XXXI.,  U.  S.  Oeol.  Surv.,  p.  210. 

f  Doelter,  Allgemeine  Chemische  Geologic,  Leipzig,  1900,  p.  158. 

1  Journal  of  Geology,  vol.  vii.,  No.  4,  p.  393. 

$  W.  Lindgren,  17th  Ann.  Rept.  U.  S.  Geol.  Surv.,  part  ii.,  p.  153. 


METASOMATIC    PROCESSES   IN   FISSURE-VEINS.  527 

formed  into  a  coarse-grained  magnesite,  mixed  with  quartz  and 
some  residual  serpentine  (Fig.  26).  The  composition  of  the  al- 
tered rock  is 

Per  cent. 

Magnesic  carbonate,       ,        .'      .'      «        •  •        •     34.78 

Calcic  carbonate,  .  i  '.  ,Y  <'!*  '.  .;  .  .  8.22 
Quartz,.  .  .  ..,;</. ;:?.  ••  •  26.00 
Serpentine  (with  chlorite),  .  .,  .  ,  ...  ,  .  31.00 

100.00 

The  chemical  action  involves  a  substitution  of  C02  for  Si02 ; 
the  latter  being  deposited  in  the  rock. 

Siderite. — This  mineral  is  less  common  in  altered  rocks  than 
the  other  carbonates.  At  Aspen,  Colorado,  Spurr  mentions  it 
as  forming  small  rhombohedrons  in  silicified  limestone.  In  the 
lead-silver  veins  of  Wood  River,  Idaho,  it  replaces  calcareous 
shales.  In  the  lead-silver  veins  of  Coeur  d'Alene,  Idaho,  it 
replaces  the  clastic  quartz  of  quartzite  in  the  most  energetic 
manner  and  abundant  quantity  (Figs.  16  and  17).  The  siderite 
has  strong  tendency  to  crystal  development ;  and  the  rhombo- 
hedral  crystals  often  cut  squarely  across  the  quartz  grains 
which  they  partly  replace  (Fig.  18).  To  explain  the  chemistry 
of  this  process,  we  must  suppose  waters  exceedingly  rich  in  al- 
kaline and  ferrous  carbonates  and  poor  in  silica.  Si02  must  be 
dissolved  and  FeC03  simultaneously  deposited. 

Muscovite  and  Sericite. — These  two  names  practically  signify 
the  same  mineral,  though  sericite  is  employed  for  the  fine- 
grained or  fibrous  and  tufted  modifications,  resulting  from  the 
replacement  of  other  minerals.  Sericite  is  probably  the  most 
universal  and  abundant  of  all  minerals  forming  in  altered  rocks 
near  fissures.  Only  a  few  classes  of  ore-deposits,  namely,  those 
in  limestone  and  those  in  recent  volcanic  rocks,  involving  pro- 
pylitic  alteration,  are  comparatively  free  from  it.  A  vast  pro- 
portion of  so-called  "  talc,"  "  clay "  and  "  kaolin "  is  really 
sericite. 

Sericite  forms  from  quartz  in  many  rocks,  though  this  action 
is  less  intense  than  in  the  case  of  the  silicates.  Foils  and  fibers 
of  the  secondary  mineral  may  develop  along  cracks,  or  may  in- 
trude, sharply  defined,  into  the  quartz,  from  the  outside  of  the 
grain.  Complete  pseudomorphs  after  quartz  are  rare.  A  com- 
plex chemical  action  is  probably  involved,  as  sericite  is  practi- 


528  METASOMATIC    PROCESSES    IN   FISSURE-VEINS. 

cally  insoluble.  A  transportation  of  potash  and  alumina  must 
be  assumed,  though  in  what  form  the  latter  oxide  was  in  solu- 
tion is  not  clear.  The  dissolved  quartz  may  be  directly  com- 
bined with  these  two  constituents.  It  is  often  observed  that 
the  replacement  of  the  quartz  is  most  active  when,  together 
with  the  sericite,  calcite  is  formed  (Fig.  15). 

As  is  well  known,  sericite  forms  easily  and  abundantly  from 
orthoclase  and  microcline,  the  foils  and  fibers  developing  on 
cleavage-planes  and  cracks,  until  they  invade  the  whole  crys- 
tal. The  reaction  may  be  chemically  expressed  as  follows, 
water  containing  carbon  dioxide  being  the  only  reagent  neces- 
sary: 

3K  Al  Si3  08  +  H20  +  C02  =  KH2  Al.  (Si04)3  +  K2CO3  +  6Si02. 

This  reaction  is  accompanied  by  a  considerable  reduction  of 
volume,  the  sericite  occupying  less  than  one-half  of  the  original 
volume  of  the  orthoclase.  If  Si02  separates  as  quartz,  the  ag- 
gregate volume  of  the  two  secondary  minerals  shows  a  reduction 
of  13  per  cent,  from  the  volume  of  the  orthoclase.  Very  often, 
however,  the  quartz  is  carried  away  in  solution,  to  be  deposited 
in  neighboring  open  spaces.  Calcite  is  frequently  deposited 
together  with  sericite  in  the  feldspar  (Fig.  12).  Though  it  is 
usually  fine-grained,  large  foils  may  sometimes  be  formed.  Fig. 
19  shows  radial  muscovite  forming,  together  with  kaolinite  from 
orthoclase,  in  the  orthoclase  of  granite  adjoining  a  fissure,  in 
which  thermal  waters  at  the  present  time  are  depositing  a  vein.* 

Sericite  forms  with  equal  ease  from  oligoclase,  andesine  and 
labradorite,  as  from  orthoclase,  and  calcite  usually  also  accom- 
panies it.  This  interesting  fact  was  first  described,  I  believe,  by 
Bischof,f  who  also  furnished  the  chemical  explanation.  The 
potassic  carbonate  contained  in  the  water  changes  the  sodic 
silicate  into  potassic  silicate,  which  unites  with  the  aluminum 
silicate  to  sericite.  This  will  result  in  a  progressive  elimina- 
tion of  soda  and  introduction  of  potash.  In  the  same  manner 
potassic  carbonate  decomposes  calcic  silicate,  replacing  lime 
with  potash.  Bischof  gives  an  excellent  illustration  of  this  by 
describing  the  surface  alteration  of  a  knife  of  the  "  stone  age," 
originally  made  from  some  flinty  rock. 

*  Kindly  furnished  by  Mr.  W.  H.  Weed. 

f  Bischof,  Chem.  GeoL,  i.,  p.  31,  et  seq.  ;  also  p.  44. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  529 

Even  pyroxene  and  amphibole  may  alter  to  sericite,  as  is 
frequently  shown  in  the  metasomatic  vein-rocks  of  California 
gold-quartz  veins.  The  explanation  is  on  the  lines  of  the  re- 
actions just  described.  The  resulting  sericite  is  often  coarsely 
fibrous. 

Biotite  alters  very  easily  to  coarse  muscovite,  with  loss  of 
magnesia  and  iron,  and  separation  of  rutile  (Fig.  27). 

An  instance  of  replacement  of  andalusite  by  muscovite  is 
shown  in  Fig.  20.  Few  analyses  are  available,  indicating  the 
exact  composition  of  the  sericite  contained  in  metasomatic 
vein-rocks ;  but  the  satisfactory  results  obtained  from  the  cal- 
culation of  many  rock-analyses  on  the  basis  of  molecular  ratio, 
closely  corresponding  to  the  composition  given  below,  leave 
little  room  for  doubt  that  the  sericite  is  practically  identical  in 
composition  with  a  normal  muscovite. 

Prof.  Beck,  of  Freiberg,  has  had  the  kindness  to  give  me  an 
unpublished  analysis,  made  by  Dr.  H.  Schulze,  of  a  white  mica, 
separated  by  Prof.  Stelzner  by  heavy  solutions  from  the  altered 
country-rock  adjoining  the  Dietrich  Stehenden,  Morgenstern 
Erbstolln,  Himmelfahrt  mine,  Freiberg.  This  analysis  is  as 
follows : 

Per  cent. 

SiO2,  ...         ...         .        .  .  47.48 

TiO2,  .        .        .       V       .        ...        .  .  trace 

SnO2,  .         ..'      ,        V    •    *   ;     ..       '.        I  •      .  .      0.02 

A12O3,  -     -   •        ...  r  •••.,..,.,.       .        .  .  35.16 

Fe2O3,  ...        ,        ...        ...  .      1.92 

CaO,  .      '.        ,        .         .        .    "    .        .       '.-  .       0.48 

MgO,  .        .        .        .        .    '".  '     .        .        r  .      1.11 

K2O,  .        .       ..    >••   .        .         ...        .        ^  .  10.08 

Na2O,  .        .  .      *    ,|-i      :.        ,        .        .        .  .       0.41 

H20,  ...        ......  .  4.02 

100.68 

As  minerals  most  closely  related  to  muscovite,  we  may  men- 
tion zinnwaldite,  containing  much  fluor  and  lithia,  which  re- 
places feldspar  in  granite  near  cassiterite-veins  ;  also  mariposite 
(fuchsite),  containing  chromium,  which,  with  magnesite,  ap- 
parently replaces  serpentine  and  allied  rocks  at  Nevada  City, 
and  on  a  much  larger  scale  at  many  places  along  the  Mother 
Lode  of  California. 

Biotite. — Exceedingly  common  in  the  form  of  metamorphism, 
biotite  appears  but  rarely  in  fissure-veins.  Replacing  horn- 


530  METASOMATIC    PROCESSES   IN   FISSURE-VEINS. 

blende  and  feldspars,  it  is  found  as  small  scales  in  veins  carrying 
tourmaline  (Meadow  Lake,  Cal.) ;  replacing  the  same  minerals, 
it  appears  abundantly  in  the  gold-copper  veins  of  Rossland, 
B.  C.  A  greenish  mica,  probably  biotite,  occurs,  replacing 
quartz,  in  small  veinlets,  associated  with  quartz,  garnet,  tour- 
maline, actinolite  and  zinc-blende,  in  the  Bunker  Hill  and  Sul- 
livan mine,  Idaho.  Prof.  Penrose  reports  secondary  biotite 
forming  in  the  Ocean  "Wave  mine,  Cripple  Creek,  Col.  Under 
the  influence  of  waters  containing  carbon  dioxide  or  alkaline 
carbonates,  biotite  is  not  stable. 

Chlorite. — This  mineral,  replacing  amphibole,  pyroxene  and 
biotite,  is  commonly  found  in  altered  vein-rocks,  but  ordinarily 
it  is  only  a  transition-form,  often  abnormally  rich  in  iron,  which 
these  minerals  assume,  under  the  influence  of  waters  slightly 
charged  with  carbon-dioxide,  before  their  final  conversion  into 
sericite  and  carbonates.  The  chlorite  has  the  ordinary  fine 
fibrous  character  and  shows  a  strong  tendency  to  migrate  into 
adjoining  minerals.  In  the  case  of  biotite,  the  conversion 
should  normally  result  in  chlorite,  ferrous  carbonate,  potassic 
carbonate  and  silica;  in  that  of  amphibole  or  pyroxene,  calcic 
carbonate  may  form  beside  chlorite.  Pseudomorphs  of  chlor- 
ite and  quartz  after  hornblende  are,  in  fact,  very  common 
(Fig.  6).  The  chloritic  alteration  is  most  important  in  the 
group  of  the  propylitic  veins.  Possibly,  under  the  influence  of 
strong  alkaline  carbonates  and  carbon  dioxide,  chlorite  can- 
not exist.  Gr.  F.  Becker  mentions  chlorite  as  enclosed  in  vein- 
quartz  from  some  localities  in  the  Southern  Appalachians,  and 
also  in  gold-quartz  veins  from  Funter's  Bay  and  Admiralty 
Island,  Alaska.  I  have  described  a  similar  occurrence  in  an 
abnormal  vein,  from  Crown  Point  mine,  Grass  Valley,  Cal. 
But,  on  the  whole,  it  is  not  a  common  mineral  in  vein-fillings. 

Pyroxene  and  Amphibole. — These  minerals  are,  as  a  rule,  for- 
eign to  fissure-veins,  and  entirely  absent  from  gold-  and  silver- 
veins  characterized  by  sericitic  alteration.  Amphibole  has 
been  noted  in  the  filling  of  certain  copper-veins.  Some  of 
these  are  more  or  less  intimately  connected  with  contact-meta- 
morphism;  others,  like  the  copper-veins  of  Rossland,  B.  C., 
have  probably  been  formed  under  dynamic-metamorphic  con- 
ditions. It  occurs  also  in  small  veinlets  of  abnormal  character, 
containing  garnets,  in  the  Bunker  Hill'  and  Sullivan  lead-silver 
mine,  Idaho.  Rhodonite,  a  bisilicate  of  manganese  allied  to  pyr- 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  531 

oxene,  does,  however,  occur  in  many  veins  as  part  of  the  fill- 
ing (Butte,  Montana ;  Real  del  Monte,  Mexico ;  Kapnik,  Hun- 
gary ;  Broken  Hill,  Australia). 

Garnet. — This  mineral  is  very  rare  in  fissure-veins,  though 
common  in  dynamic  and  contact-metamorphism.  Mr.  S.  F. 
Emmons*  states  that  it  replaces  limestone  at  Clifton,  Arizona, 
apparently  as  a  part  of  the  phenomena  of  mineralization.  As 
part  of  the  filling  of  gold-quartz  veins,  it  is  reported  by  G.  F. 
Becker t  from  several  localities  in  the  Southern  Appalachians. 
The  remarkable  occurrences  of  Broken  Hill,  N.  S.  W.,  should 
be  mentioned  here.  From  the  extensive  literature!  it  is 
apparent  that  opinions  differ  somewhat  widely  with  regard  to 
these  interesting  deposits. 

The  deposits  of  the  Barrier  ranges  near  Broken  Hill  are 
probably  fissure-veins,  occurring  in  crystalline  schists  of  various 
kinds,  perhaps  chiefly  a  garnet-gneiss.  Broken  Hill  Proprie- 
tary lies  parallel  to  the  schistosity,  and  may,  according  to 
some,  be  considered  as  a  saddle-reef.  Other  veins,  such  as  the 
Broken  Hill  Consols,  cut  the  schistosity  in  strike  and  dip.  The 
ores  are  galena,  zinc-blende  and- rich  silver-ores.  The  gangue 
in  the  Proprietary  mine  is  chiefly  garnet,  with  quartz,  opal  and 
rhodonite.  In  the  Consols  and  other  veins,  siderite  and  calcite 
also  appear,  besides  quartz  and  garnet.  If  veins,  as  seems 
most  probable,  they  represent  a  decidedly  novel  type.  The 
sulphides,  to  some  extent,  replace  other  minerals.  (See  under 
Galena,  below.) 

Epidote. — This  mineral,  so  common  in  regions  of  static  and 
dynamic  metamorphism,  is  not  abundant  in  the  altered  rocks 
of  fissure-veins,  or  in  the  filling  of  open  spaces.  When  it 
occurs,  it  has  a  deep  yellow  color,  contains  much  iron  and  de- 
velops in  irregular  grains,  or  into  radial  bunches  of  imperfect 
crystals.  It  occurs  chiefly  in  basic  rocks  containing  labradorite 
and  similar  soda-lime  feldspars,  and  may  form  pseudomorphs 
after  orthoclase,  plagioclase,  hornblende  or  augite.  In  altered 
vein-rocks,  epidote  and  muscovite  rarely  occur  together.  Epi- 
dote contains  much  ferric  oxide,  and  can  hardly  be  formed 

*  Unpublished  observations. 

t  16th  Ann.  Rept.  U.  S.  Geol.  Surv.,  part  iii.,  p.  276. 

t  J.  B.  Jaquet,  Mem.  5,  Geol.  Surv.  of  N.  8.  Wales,  Sydney,  1894 ;  George 
Smith,  Trans.,  xxvi.,  69,  1896  ;  E.  Beck,  Zeitschr.  f.  prakt.  Geol.,  March,  1899,  etc. 

34 


532  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

under  strong  reducing  influences.  It  does,  however,  not  follow 
that  it  must  have  been  formed  under  oxidizing  conditions  ;  for 
rocks  ordinarily  contain  much  ferric  oxide,  and  pyrite  has 
often  been  observed  embedded  in  epidote.  Epidote  is  found  in 
the  veins  of  Lake  Superior  which  carry  native  copper ;  in  some 
veins  characterized  by  tourmaline  (Fig.  21) ;  and,  finally,  in  the 
metasomatic  rocks  accompanying  the  propylitic  Tertiary  gold- 
silver  veins. 

Orthoclase. — As  a  product  of  thermal  alteration,  orthoclase 
does  not  commonly  appear,  and  has  not  been  recognized 
until  lately.  Closer  search  will  probably  reveal  it  in  many 
altered  rocks  and  vein-fillings  of  the  propylitic  type.  When 
forming,  it  has  always  a  strong  tendency  to  crystallize,  and 
in  thin  sections  usually  appears  with  rhombic,  sharply  de- 
fined outlines.  The  crystal  form  is  similar  to  that  of  adular, 
though  the  basal  plane  is  small  or  entirely  wanting ;  the  prisms 
and  dome  being  the  only  prominent  faces.  For  this  variety, 
occurring  in  fissure-veins,  the  revival  of  the  name  of  valenci- 
anite  is  suggested,  proposed  by  Breithaupt  for  the  mineral  as 
occurring  in  the  Yalenciana  silver-mine,  Guanajuato,  Mex.  In 
certain  propylitic  gold-silver  veins  (Silver  City,  Idaho ;  La  Ya- 
lenciana, Mex.)  valencianite  is  prominent  as  part  of  the  filling 
of  open  spaces.  In  the  copper-bearing  veins  of  Lake  Superior, 
orthoclase  replaces  prehnite,  and  is  deposited  on  datolite,  calcite, 
anal  cite  and  quartz.  In  connection  with  the  occurrence  of  adular 
at  St.  Gothard,  this  mineral  is  found  on  calcite.  At  Bergen 
Hill,  E".  J.,  the  Mesozoic  diabases  are  traversed  by  veins  (1  to  4 
inches  thick)  of  quartz  and  orthoclase,  associated  with  various 
zeolites,  galena,  chalcopyrite  and  pyrite.  At  Cripple  Creek, 
Colo.,  orthoclase  is  an  important  vein-mineral,  occurring  partly 
as  a  coating  of  cavities  of  dissolution  in  granite  (Fig.  11),  partly 
in  metasomatic  development  after  many  minerals  in  granite- 
andesite  breccia  and  phonolite.  Orthoclase  and  calcite  have 
apparently  been  formed  together  in  certain  metasomatic  rocks 
from  Cripple  Creek,  Colo. 

Orthoclase  has  been  reproduced  artificially  by  the  action  of 
potassic  silicate  on  muscovite  at  500°  C.,  but  it  is  evident  from 
many  occurrences  that  a  much  lower  temperature  is  sufficient 
for  its  formation  in  fissure-veins.  In  the  Silver  City,  Idaho, 
veins,  for  instance,  the  temperature  xjannot  have  been  much 
higher  than  100°  C.  during  the  deposition  of  the  mineral. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  533 

Albite. — Though  known  as  a  vein-filling,  together  with  quartz, 
at  many  places,  for  instance,  in  many  California  gold-quartz 
veins,  this  mineral  has  not  been  observed  hitherto  replacing  other 
substances.  In  metasomatic  rocks  resulting  from  other  meta- 
morphic  processes  it  is,  as  is  well  known,  very  abundant. 

Tourmaline. — This  very  complex  silicate  of  aluminum,  magne- 
sium, ferric  iron  and  sodium  contains  also  about  10  per  cent,  of 
boric  acid,  as  well  as  a  little  combined  water  and  fluorine.  In 
metasomatic  development,  it  forms  irregularly  massed  crystals, 
or  single  crystals  impregnating  the  mother-mineral.  Its  ten- 
dency to  crystallization  is  very  strongly  marked.  It  replaces 
orthoclase  and  plagioclase,  as  well  as  quartz,  but  is  not  known 
to  be  formed  from  ferromagnesian  minerals.  As  shown  in  Fig. 
21,  small  almost  perfect  crystals  may  develop  in  the  feldspathic 
substance,  without  disturbing  its  optical  orientations.  Similar 
development  in  quartz  is  illustrated  in  Fig.  23.  In  fine-grained 
clastic  rocks  like  slate,  tourmaline  may  also  form.  The  only 
occurring  variety  is  black,  usually  showing  dark  brown  and 
dirty  bluish  or  greenish  colors  in  thin  section.  Tourmaline 
often  occurs  in  large  masses  of  small  felted  individuals,  together 
with  quartz,  entirely  replacing  the  original  rock. 

The  mineral  is  confined  to  cassiterite-veins  and  to  the  allied 
group  of  the  gold-copper-tourmaline  veins.  It  is  not  usually 
associated  with  carbonates;  and  the  occurrence  of  siderite  with 
tourmaline,  described  by  von  Fircks  from  Tasmania,*  is  there- 
fore of  special  interest. 

Topaz. — This  fluosilicate  of  aluminum,  containing  besides, 
according  to  the  latest  investigations,  some  chemically  com- 
bined water,  is  confined  to  the  cassiterite-veins.  It  usually  ap- 
pears abundantly  in  the  altered  rock  next  to  these  veins,  re- 
placing the  feldspar  and  even  the  quartz, f  as  well  as  the 
groundmass  of  porphyritic  rocks.  The  new-formed  topaz  may 
appear  in  irregular  grains,  but  is  often  partly  crystallized,  and 
then  appears  in  radial  masses.  The  formation  of  topaz  from 
orthoclase  is  analogous  to  kaolinization,  silica  and  potassa  being 
set  free.  But  fluorine  is  also  introduced,  which  points  to 
another  agent  than  carbon  dioxide  as  active  in  this  reaction. 
It  has  been  artificially  reproduced  by  the  action  of  hydro- 

*  Zeitsch.  d.  d.  geol.  Ges.,  Bd.  li.,  p.  443,  1899.  f  Loc.  cit.,p.  444. 


534  METASOMATIC    PROCESSES   IN   FISSURE-VEINS. 

fluosilicic  acid  on  silica  and  alumina.    Topaz  is  not  very  stable. 
It  is  easily  altered  to  kaolinite  or  sericitic  minerals. 

Kaolinite. — The  hydrous  silicate  of  aluminum  was  formerly 
supposed  to  occur  very  extensively  in  altered  vein-rocks ;  but 
it  has  been  shown  that  the  larger  part  of  the  minerals  consid- 
ered as  kaolinite  or  as  "  talc  "  are  really  sericite  in  finely  di- 
vided form.  Kaolinite  forms  from  orthoclase,  albite  or  soda- 
lime  feldspars,  with  liberation  of  silica,  the  reaction  in  the  first 
case  being  expressed  as  follows  : 

6  (K  Al  Si3  08)  +  6H20  +  3C02  =  3  (H4  A12  Si2  O9)  + 
3KC03  +  12Si02. 

Ferromagnesian  silicates,  and  even  quartz,  may  be  converted 
into  kaolinite,  as  is  shown  by  the  altered  rock  adjoining  a  re- 
cent vein  near  Boulder,  Montana.  The  mineral  is  nearly 
always  in  an  extremely  fine  state  of  distribution ;  the  aggre- 
gates have  a  very  low  bi-refracting  power.  Kaolinite  and  seri- 
cite may  form  together  (Fig.  19),  as  is  also  shown  by  the  cal- 
culated composition  of  many  altered  rocks.  Wherever  abun- 
dant carbonates  form,  metasomatically,  together  with  sericite, 
kaolinite  seems  to  be  absent.  It  often  occurs  oa  cassiterite- 
veins  (though  it  is  possible  that  the  kaolinite  may  here  be  simply 
a  secondary  alteration  of  topaz) ;  further,  together  with  sericite, 
in  veins  of  the  pyritic  galena-formation  of  Freiberg;  in  some 
veins  of  propylitic  character,  as  at  Cripple  Creek,  and  in  veins 
where  the  action  of  stronger  reagents,  such  as  sulphuric  acid, 
seems  probable  (Summit  District,  Colo.,*  De  Lamar,  Idahof). 
Kaolinite  is  formed  most  abundantly  in  the  upper,  oxidized 
zones  of  many  ore-deposits. 

Zeolites. — These  hydrated  minerals  are  almost  completely  ab- 
sent from  fissure-veins.  Exceptions  are  the  silver  veins  of  An- 
dreasberg  in  the  Hartz,  and  Kongsberg  in  Norway,  where  many 
zeolites  occur  as  vein-filling  with  quartz  and  calcite.  As  meta- 
somatic  minerals,  they  occur  in  the  Lake  Superior  copper-veins 
replacing  feldspars  and  other  minerals.  Daubree  has  described 
zeolites  forming  in  old  bricks  at  Plombieres,  by  the  action  of 
thermal  waters  ascending  on  a  vein  which  does  not  contain  any 

*  R  C.  Hills,  Proc.  Colorado  Sci.  Soc.,  vol.  i.,  pp.  20-36. 

f  W.  Lindgren,  2/OthAnn.  Rept.  U.  S.  Geol.'Surv.,  partiii.,  pp.  171,  172. 


METASOMATIC    PROCESSES   IN   FISSURE-VEINS.  535 

of  these  minerals.  W.  H.  "Weed  finds  stilbite  with  quartz  as 
the  filling  of  a  recent  vein  by  ascending  hot  waters  at  Boulder, 
Montana.  The  absence  of  the  zeolites  from  veins  is  some- 
what difficult  to  explain,  as  it  is  well  known  that  many  of  them 
may  be  formed  at  very  widely  differing  pressures  and  tempera- 
tures. Very  slight  modifications  of  condition  may  result  in  the 
formation  of  hydrous  or  anhydrous  minerals.  Thus,  for  in- 
stance, Friedel  and  Sarasin*  found  that  when  a  solution  of  sili- 
cate of  sodium  mixed  with  silicate  of  aluminum,  in  proportions 
required  to  form  albite,  was  heated  to  500°  C.  in  a  closed 
tube,  analcite  was  formed.  When  excess  of  the  alkaline  silicate 
was  used,  albite  resulted. 

Pyrite. — Of  all  the  sulphides  occurring  as  metasomatic  min- 
erals pyrite  is  naturally  the  most  common.  In  most  fissure- 
veins,  it  impregnates  the  adjoining  rock  in  varying  amounts, 
even  if  the  alteration  in  other  respects  has  not  progressed  far. 
The  mineral  has  a  remarkable  tendency  to  crystallization  when 
developing  in  the  rock,  as  contrasted  with  its  often  massive 
texture  when  occurring  as  a  filling  of  open  spaces.  The  forms 
assumed  are  either  cubes  or  pentagonal  dodecahedrons,  or  a 
combination  of  both. 

Pyrite  develops  in  nearly  every  one  of  the  ordinary  con- 
stituents of  rocks.  By  preference,  it  forms  in  the  new  aggre- 
gates of  sericite,  carbonates  and  chlorite  so  common  in  altered 
rocks ;  but  it  also  occurs  in  the  fresh  original  minerals  of  the 
rocks,  as  in  quartz,  feldspar,  hornblende  and  pyroxene.  It  is  also 
abundant  in  calcareous  shales  adjoining  veins.  It  is  common 
to  find  small,  sharp  crystals  embedded,  for  instance,  in  perfectly 
clear  quartz  grains,  which  show  no  break  in  their  optical  orienta- 
tion around  the  secondary  crystal,  proving  that  the  genesis  is  by 
purely  metasomatic  processes,  and  not,  as  may  be  advocated  in 
the  case  of  crystallization  in  soft  aggregates,  by  the  mechanical 
pressure  of  the  growing  crystal.  On  the  other  hand,  the  devel- 
opment of  a  larger  crystal  in  quartz  or  feldspar  will  often  pro- 
duce a  breaking-up  of  the  grains  as  an  optical  unity,  and  the 
substitution  for  it  of  an  interlocking  aggregate  of  smaller 
grains.  To  what  force  this  is  due  is  not  certain ;  there  are 
usually  no  indications  of  direct  pressure  from  the  growing 
crystal. 

*  Comptes  rendus,  Acad.  des  Sci.,  Paris,  July,  1883,  vol.  xcvii.,  p.  291. 


536  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

The  pyrite  crystals  are  often  bordered  by  a  small  rim  of  cal- 
cite  or  quartz ;  and  little  bunches  of  sericitic  fibers  may  adhere 
to  them,  when  forming  in  quartz.  On  the  whole,  the  pyrite 
seems  to  obtain  some,  if  not  all,  of  its  iron  from  the  ferro-mag- 
nesian  minerals,  rather  than  from  the  magnetite  and  titanifer- 
ous  ores,  which  appear  to  alter  to  carbonates  and  rutile. 

Marcasite. — In  metasomatic  development,  this  mineral  is  rare, 
though  it  has  been  observed  accompanied  with  kaolin,  at  De 
Lamar,  Idaho,  as  the  result  of  the  hydrothermal  alteration  of 
rhyolite.*  It  is  always  crystallized,  and  the  individuals  com- 
bine to  arborescent  forms. 

Chalcopyrite. — This  mineral  is  not  common  in  the  metasomatic 
rocks  of  gold-  and  silver-veins,  but  it  forms  abundantly  in  cer- 
tain replacement-veins,  such  as  those  of  Butte,  Mont,  and  Ross- 
land,  B.  C.  In  such  cases,  it  may  replace  any  of  the  ordinary 
rock-forming  minerals.  It  forms  in  irregular  masses,  is  rarely 
crystallized,  and  is  frequently  accompanied  by  a  narrow  lining 
of  chlorite. 

Arsenopyrite. — Like  pyrite,  arsenopyrite  nearly  always  forms 
in  crystals ;  these  show  the  simple  combination  of  rhombic 
prisms  and  striated  dome,  and  may  also  replace  any  of  the  rock- 
forming  minerals.  Next  to  pyrite  it  is  the  most  common  sul- 
phide in  the  altered  rocks  adjoining  veins. 

Pyrrhotite. — This  mineral  is  not  abundant  either  in  vein-fill- 
ing or  in  metasomatic  rocks.  Indeed,  in  many  classes  of  veins 
it  is  entirely  absent;  and  if  it  happens  to  be  present  in  the 
rock  close  to  the  vein,  it  may  suffer  alteration  to  pyrite  under 
the  influence  of  the  vein-forming  agencies. f  As  a  product  of 
replacement  of  feldspar  and  ferro-magnesian  silicates,  it  occurs 
in  the  Rossland  veins  of  British  Columbia,  associated  with 
chalcopyrite.  The  conditions  governing  the  formation  of 
pyrrhotite  are  not  fully  known.  It  has  been  artificially  repro- 
duced, but  not  under  conditions  which  seem  analogous  to  those 
of  nature.  At  any  rate,  the  mineral  can  only  be  formed  under 
very  strongly  reducing  influences. 

Galena. — By  preference,  galena  replaces  calcite  and  dolomite. 
Hence  the  great  abundance  of  metasomatic  galena-deposits  in 

*  20th  Ann.  Eept.  U.  S.  Geol.  Surv.,  part  iii.,  p.  169. 
f  17th  Ann.  Eept.  U.  S.  Geol.  Surv., -part  ii.,  p.  147. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  537 

limestone,  calcareous  shale  and  similar  rocks.  In  crystalline 
igneous  or  metamorphic  rocks,  it  is  not  abundant  as  a  metaso- 
matic  product.  But  it  may  replace  other  minerals,  especially 
quartz.  Metasomatic  galena  scarcely  ever  appears  in  crystal- 
line form,  but  often  forms  wiry,  extremely  irregular  masses.  Fig. 
25  shows  its  appearance  in  primary  quartz  of  a  quartz-diorite. 
It  only  occurs  in  quartz  which  is  completely  filled  with  fluid  in- 
clusions; and  its  growth  begins  as  little  knots  and  particles, 
dotted  over  any  given  plane  of  fluid  inclusions.  These  dots, 
of  which  some  are  shown  in  the  figure,  finally  appear  to  have 
united  to  larger  masses.  The  quartz  grain  in  which  the  galena 
occurs  is  partly  broken  up  into  new  quartz  aggregates.  Galena 
replacing  quartz  in  quartzite  from  Northern  Idaho  is  shown  in 
Fig.  16.  Gradually  extending,  the  galena  unites  to  larger 
masses,  as  illustrated  in  Fig.  17. 

The  replacement  of  calcite  by  galena  is  illustrated  by  Fig. 
29,  representing  part  of  a  section  from  the  Elkhorn  mine, 
Montana,  which  Mr.  W.  H.  Weed  kindly  put  at  my  disposal. 
The  rock,  a  crystalline  limestone,  apparently  free  from  organic 
matter,  contains  small,  partly  idiomorphic  quartz  grains,  scat- 
tered among  the  larger  grains,  and  also  many  small  veinlets  of 
secondary  quartz.  There  is  thus  at  least  an  incipient  silicifica- 
tion  accompanying  the  formation  of  the  galena.  In  the  little 
quartz  veins  and  throughout  the  rock  are  small,  sharply  defined 
pentagonal  dodecahedrons  of  pyrite,  nearly  always  connected 
with  small  quartz  grains.  The  galena  appears  in  several 
smaller  grains  closely  intergrown  with  pyrite ;  also  in  larger 
masses  surrounded  by  a  narrow  rim  of  pyrite,  and  by  clusters 
of  small  secondary  grains  and  crystals  of  quartz.  The  galena 
is  not  clearly  crystallized,  but  appears  in  small,  solid  masses, 
developing  along  the  cleavage  planes  of  calcite  so  that  rhombo- 
hedral  grains  of  the  latter  may  be  almost  surrounded  by  galena. 

Concerning  the  chemical  reactions  involved  in  the  replace- 
ment by  galena  opinions  differ.  Some  think  that  the  slightly 
soluble  sulphate  of  lead  is  reduced  from  solutions  by  organic 
matter — and  adduce  as  confirmation  the  universal  occurrence 
of  galena  in  limestone  or  other  sedimentary  rocks,  presumably 
containing  organic  matter.  Another  view  is  that,  the  sulphide 
of  lead  being  soluble  to  a  considerable  extent  in  water  contain- 
ing sodic  sulphide  (Doelter),  a  simple  precipitation  from  solu- 


538  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

tion  has  taken  place,  dependent  on  the  simultaneous  solution  of 
limestone  and  separation  of  silica. 

For  most  cases  I  would  be  inclined  to  the  latter  view,  since 
the  small  quantity  of  organic  matter  available,  for  instance  in 
the  Elkhorn  limestone  or  in  the  Coeur  d'Alene  quartzite, 
seems  utterly  insufficient  to  reduce  such  large  masses  of 
galena  as  are  found  at  these  localities.  Besides,  silver-lead 
veins  may  occur  in  the  same  districts  in  very  different  rocks. 
Thus,  for  instance,  in  the  Wood  River  region,  Idaho,  they  are 
found  not  only  in  the  limestone  but  also  in  granite,  which  cer- 
tainly does  not  contain  organic  substances. 

In  this  connection  should  be  mentioned  the  replacement  of 
rhodonite  by  galena  and  zinc-blende,  described  and  figured  from 
Broken  Hill,  Australia,  by  Prof.  R.  Beck.  From  the  same  local- 
ity Mr.  Jaquet  described  and  figured  galena  replacing  ortho- 
clase ;  and  a  silver  mineral,  probably  argentite,  replacing  gar- 
net, and  perhaps  quartz,  in  a  garnet  schist. 

Zinc-blende  and  Other  Sulphides. — In  metasomatic  occurrence 
zinc-blende  is  extremely  similar  to  galena.  It  is  usually  found 
as  irregular  grains,  replacing  limestone,  quartzite  (Fig.  17), 
and  many  minerals  in  igneous  rocks. 

Much  additional  material  might  be  quoted  regarding  the  re- 
placement of  rocks  by  other  sulphides ;  the  literature  on  the 
subject  should  be  used,  however,  with  care,  since  critical 
studies  of  the  modes  of  replacement  are  very  few,  and  some 
statements  are  simply  based  on  casual  inspection  with  the 
naked  eye. 

Many  other  sulphides  are  undoubtedly  formed  by  metaso- 
matic replacement.  Enargite,  for  instance,  is  noted  by  Em- 
mons*  as  replacement  thus  present  in  the  altered  vein-rock  of 
Butte,  Mont. 

Tellurides. — Tellurides  of  gold  and  silver  are  found  at  Crip- 
ple Creek  and  elsewhere,  under  circumstances  indicating  meta- 
somatic deposition. 

Native  Copper. — This  metal  replaces  many  minerals.  Ac-. 
cording  to  Pumpelly,f  it  replaces  feldspar  and  various  zeolites 
in  the  Lake  Superior  amygdaloids;  and  most  of  the  large 
masses  of  copper  there  found  are  believed  to  be  metasomatic. 

*   U.  S.  Geol.  Surv.,  Folio  38. 

f  Geol.  Surv.  Mich.,  vol.  i.,  part  ii.,  p.  19,  et  seq. 


METASOMATIC    PROCESSES   IN    FISSURE-VEINS.  539 

Gold  and  Silver.— Native  gold  and  silver  are  likewise  impor- 
tant results  of  replacement  in  many  veins.  It  is  well  known 
that  masses  of  these  metals  are  occasionally  found  in  the 
country-rock  away  from  the  fissure ;  and  these  occurrences  are 
probably  to  be  interpreted  as  metasomatic,  though  the  process 
has  not  been  followed  in  its  details. 

Gold  is  also  often  contained  in  the  replacing  pyrite  and  other 
sulphides;  and  free  gold  can  be  obtained  by  panning  from  cer- 
tain kinds  of  altered  vein-rock.  But  caution  should  always  be 
observed  in  stating  such  observations.  I  have  known  instances 
of  supposed  replacement  where,  in  fact,  all  the  value  was  de- 
rived from  the  filling  of  minute  fissures  and  cracks. 

Resistant  Minerals. 

Among  the  minerals  which  yield  not  at  all  or  only  with  dif- 
ficulty to  metasomatic  influences  are  apatite,  muscovite,  zircon 
and  chromite.  The  resistance  of  apatite  is  very  remarkable ; 
for  according  to  R.  Miiller*  apatite  is  soluble  with  comparative 
ease  in  water  containing  carbon-dioxide. 

PART  in. 

THE  FISSURE- VEINS  CLASSIFIED  ACCORDING  TO  METASOMATIC 

PROCESSES. 

Under  this  head,  I  suggest  fourteen  classes  of  fissure-veins, 
each  usually  characterized  by  its  own  distinctive  metasomatic 
process.  These  fourteen  divisions  are  not  offered  as  a  per- 
manent classification,  though  most  of  them  are  sharply  defined. 
The  principle  is  not  unqualifiedly  good  for  a  genetic  classifica- 
tion, for  the  reason  that  the  same  waters  may  cause  a  different 
metasomatic  development  in  different  rocks. 

The  list,  in  each  title  of  which  the  first  word  indicates  the 
predominant  metasomatic  mineral  or  process,  is  as  follows :  1. 
Topaz-cassiterite  veins;  2.  Scapolite-apatite  veins;  3.  Tour- 
malinic  gold-copper  veins;  4.  Biotitic  gold-copper  veins;  5. 
Propylitic  gold-  and  silver-veins;  6.  Fluoritic  gold-tellurium 
veins ;  7.  Sericitic  and  kaolinic  gold-  and  silver-veins ;  8.  Seri- 
citic  and  calcitic  gold-  and  silver-veins ;  9.  Silicic  and  calcitic 
quicksilver-veins;  10.  Sericitic  copper-silver  veins ;  11.  Silicic 

*  Tsch.  Min.  Mitt.,  p.  25,  1877- 


540  METASOMATIC    PROCESSES   IN    FISSURE-VEINS. 

and  dolomitic  silver-lead  veins ;  12.  Sideritic  silver-lead  veins ; 
13.  Sericitic  silver-lead  veins ;  14.  Zeolitic  copper-  and  silver- 
veins. 

1.    Topaz- Cassiterite  Veins. 

This  sharply  defined  class  is  characterized  by  exceedingly 
strong  metasomatic  action,  with  fluorine  as  mineralizing  agent, 
resulting  in  often  coarse-grained,  altered  rocks,  containing 
topaz  and  sometimes  tourmaline,  besides  an  often  considerable 
percentage  of  cassiterite. 

The  cassiterite-veins  are  characterized  by  their  occurrence  in 
connection  with  intrusive  igneous  rocks.,  and  by  the  pneumato- 
lytic  change  of  the  country-rock  to  greisen,  a  granular  rock 
consisting  chiefly  of  quartz,  topaz  and  white  mica,  usually  con- 
taining fluor  and  lithia.  Tourmaline  and  cassiterite  are  usually 
accessory  constituents  of  this  rock.  The  feldspar  and  the 
brown  mica  of  the  original  rock  are  destroyed,  and  the  min- 
erals mentioned  above  are  added.  Topaz  often  forms  pseudo- 
morphs  after  quartz;  cassiterite,  tourmaline  and  topaz,  after 
feldspar.  The  alteration  of  the  country-rock  varies  somewhat 
in  chemical  aspects,  but  is  distinguished  by  strongly  marked 
transportation  of  substance. 

In  the  granular  greisen,  the  new  minerals  appear  as  indi- 
viduals of  considerable  extent  and  optical  continuity,  perhaps 
indicating  that  the  processes  by  which  it  was  formed  were 
more  active  and  energetic  than  those  producing  the  aggregate 
structure  commonly  found  in  altered  vein-rocks.  The  minerals 
found  in  the  metasomatic  wall-rock  appear  also  in  the  fissures 
themselves ;  hence  the  same  chemical  process  must  have  been 
active  in  both.  Other  rocks,  such  as  gneiss,  quartz-porphyry 
and  rhyolite,  show  similar  alteration,  though  tin-deposits  do 
not  so  commonly  occur  in  them.  A  notable  feature  of  the  cas- 
siterite-veins is  the  occurrence  of  apatite,  a  mineral  generally 
unknown  in  fissure-veins.  Under  ordinary  circumstances,  in 
altered  vein-rocks,  apatite  is  the  last  mineral  to  remain  fresh, 
after  all  other  primary  minerals  have  been  destroyed. 

Yogt's  explanation*  of  the  genesis  of  cassiterite-veins  and 
the  alteration  of  their  wall-rocks  follows  closely  the  previously 
expressed  views  of  Elie  de  Beaumont,  Daubree,  Le  Neve  Fos- 

*  J.  H.  L.  Vogt,  Zeitschr.  f.  prakt.  Geologic,  1895,  p.  145. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  541 

ter  and  Dalmer.  He  assumes  that  they  were  formed  imme- 
diately after,  or  even  during,  the  granitic  eruptions,  and,  fur- 
ther, that  the  mineral  solutions  originated  by  the  action  of 
hydrofluoric  acid  and  hydrochloric  acid  on  the  magma,  still 
entirely  or  partly  in  igneous  fusion.  By  means  of  these,  fluor- 
ides of  silicon,  tin,  boron  and  lithium  were  extracted,  as  well 
as  phosphoric  acid.  These  solutions  took  place  under  pneu- 
matolytic  conditions,  that  is,  the  "  critical  point  "*  had  been 
passed  and  the  substances  were  present  in  a  gaseous  state  in 
spite  of  the  high  pressure.  These  extracts  in  gaseous  state 
ascended  on  the  previously  formed  fissures  and  strongly  at- 
tacked the  adjoining  country-rock,  changing  it  to  greisen  by 
means  of  replacement  by  minerals  containing  fluorine  and 
other  mineralizing  agents.  Different  rocks  were,  perhaps,  not 
affected  exactly  in  the  same  way.  For  instance,  the  altered 
product  resulting  from  schists  is  not  quite  similar  to  that  re- 
sulting from  granite,  this  being  possibly  due  to  the  fact  that 
the  schists  were  not  heated  to  such  a  degree  as  was  the  granite. 
While  the  formation  of  the  greisen  took  place  after  the  con- 
solidation of  the  rock,  as  is  evidenced  by  the  fact  that  fissures 
could  form  in  it,  still  it  is  believed  that  the  temperature  must 
have  been  very  high,  and,  in  fact,  that  the  lower  masses  of  the 
granite  were  not  yet  consolidated. 

Altenberg  and  Zinnwald,  Saxony. — The  tin-deposits  of  Alten- 
berg  and  Zinnwald,  in  Saxony,  have  been  lately  investigated 
by  K.  Dalmer. f  The  cassiterite-deposits  of  Altenberg  consist, 
as  is  well  known,  of  a  number  of  ore-fissures  which  sometimes 
carry  a  notable  amount  of  quartz,  mica  and  topaz,  as  well  as 
cassiterite.  Over  a  considerable  area  traversed  by  these  vein- 
lets  appears  a  greisen,  locally  called  zwitter,  which  Mr.  Dal- 
mer shows  to  have  resulted  unquestionably  from  the  metaso- 
matic  alteration  of  the  granite.  The  process  consisted  of  a  re- 
placement of  feldspar,  principally  orthoclase,  by  topaz  contain- 
ing lithium  and  fluorine.  The  beginning  of  the  process  is  often 

*  The  critical  temperature  for  water  is  +  365°  C.  at  a  pressure  of  200  atmos- 
pheres. For  most  other  substances  the  critical  point  is  passed  below  this  tem- 
perature and  pressure.  It  is,  perhaps,  not  needless  to  state  that  the  passing  of  the 
critical  temperature  does  not  mean  that  the  substances  are  dissociated. 

t  Erlduterungen  zur  Geologischen  Spedalkarte  des  Konigreichs  Sachsen,  Section  "Al- 
tenberg-Zinnwald,"  Leipzig,  1890. 


542  METASOMATIC    PROCESSES   IN   FISSURE-VEINS. 

visible,  small  strings  of  aggregates  of  mica  and  topaz  pervad 
ing  the  feldspar.  These  strings  repeatedly  cross  each  other, 
and  by  extension  of  the  mineral  individuals  complete  replace- 
ment is  attained.  The  greisen  consists  of:  quartz,  50.28 ;  topaz, 
12.14;  mica,  36.80;  and  cassiterite,  0.43;  total,  99.65  per  cent. 
Dr.  Dalmer  has  calculated  the  composition  of  the  rock  from 
these  percentages,  and  obtained  a  result  which  closely  agrees 
with  the  old  analysis  of  the  same  rock  by  Rube,  quoted  in 
Cotta's  G-angstudien.  The  following  table  shows  the  result,  I 
being  the  fresh  granite  and  II  the  altere'd  product : 

ii. 

Per  Cent. 

70.41 
0.49 
0.49* 

14.86 
1.42 
5.09 

0.29 
0.21 
0.09 
3.01 
0.98 
3.10 


99.50  100.44 

From  these  two  analyses  it  is  clear  that  the  formation  of 
greisen  does  not  by  any  means  involve  silicification.  Dal- 
mer concludes  that  the  principal  changes  consisted  in  the  addi- 
tion of  FeO,  Fl,  Sn02,  and  possibly  A1203,  while  K20,  Na20  and 
Si02  have  been  subtracted.  In  the  absence  of  further  knowl- 
edge of  the  relations  of  volume  during  the  alteration,  it  is 
scarcely  possible  to  conclude  from  the  comparison  of  these 
analyses  alone  what  the  actual  changes  have  been.  The  de- 
termination of  specific  gravities  of  the  rocks  would  probably 
help  to  obtain  a  clearer  insight  in  regard  to  this  matter.  This 
much  is  evident,  that  the  mineral  aggregate  of  the  granite  has 
changed  to  a  new  aggregate  of  greater  density. 

It  will  be  observed  that  the  second  analysis  contains  no  water. 
This  has  probably  been  unintentionally  omitted,  as  it  must 

*  As  cassiterite,  0.43;  in  mica,  chemically  combined,  0.06. 


SiO2, 

I. 
Per  Cent. 
-   ,•       .        .        ..         .        .     74.68 

TiO2, 

.        .        »        .      0  71 

SnO2, 

.    '    .        .        .        ..        .      0.09 

A1203,       .     •<-.' 
Fe203,      .        ,- 
FeO,         .        . 

'•'       •        f,    '•        •'       •     12.73 
3.00 

CuO, 

.        .        .-               .        .      0.50 

MnO,       . 

CaO,     ...,-       . 

«^      .....       0.09 

MgO, 

0.35 

K2O, 

4.64 

Na2O  +  LiaO,  . 
Fl,  .         .        . 
H20, 

1.54 
.        .         .        .       1.17 

METASOMATIC    PROCESSES   IN   FISSURE-VEINS.  543 

surely  be  present,  being  contained,  chemically  combined,  both 
in  topaz  and  in  the  lithium-mica. 

In  view  of  the  fact  that  in  this  alteration  not  only  the  potas- 
sium-aluminum silicate,  muscovite,  but  also  the  pure  aluminum 
fluo-silicate  or  topaz  appears,  it  is  interesting  to  note  that  m eta- 
somatic  kaolin  is  undoubtedly  present  in  cassiterite-veins. 
Pseudomorphs  of  it  after  topaz  have  been  frequently  observed, 
and  it  is  often  stated  that  "  steinmark  "  is  present  in  the  veins ; 
this  being  really  only  a  synonym  for  kaolin.  Daubree  long  ago 
called  attention  to  the  connection  of  kaolin  with  cassiterite- 
veins. 

In  several  places  the  alteration  of  the  granite  and  the  adjoin- 
ing porphyry  is  of  a  radically  different  character,  and  consists  in 
a  complete  silicification.  While  this  is  not  the  normal  process, 
yet  it  appears  fairly  common,  and  must  be  taken  into  considera- 
tion in  attempting  to  explain  the  genesis  of  these  veins. 

Mt.  JBischoff,  Tasmania  :  The  rocks  of  the  tin-deposits  of  Mt. 
Bischoff,  in  Tasmania,  have  lately  been  described  by  "W.  von 
Fircks,*  who  devotes  considerable  space  to  the  alteration  which 
they  have  suffered.  The  tin-deposits  appear  in  an  area  of 
quartzites  and  clay-slates  with  dikes  of  quartz-porphyry. 
Granite  is  present  some  distance  from  the  mines.  The  de- 
posits are  in  part  fissure-veins  carrying  cassiterite,  pyrite, 
arsenopyrite,  fluorite,  wolframite,  tourmaline  and  siderite. 
The  latter  mineral  is  notable,  because  not  usually  present  in 
veins  of  this  character.  Another  part  of  the  deposits  is  formed 
by  replacement,  chiefly  of  porphyry  dikes.  All  rocks  in  the 
vicinity  of  the  mines  are  much  altered.  The  schists  and  slates 
contain  much  tourmaline,  and  are  in  part  changed  to  typical 
tourmalin-fels  by  complete  replacement,  only  a  few  grains  of 
the  original  rock  remaining.  Besides  the  tourmaline,  some 
siderite  also  appears,  while  topaz  is  present  in  but  small  quan- 
tity. These  altered  schists  contain  cassiterite  (rare),  and  also 
pyrite,  arsenopyrite,  pyrrhotite,  fluorite,  calcite,  siderite  and 
pyrophyllite  as  metasomatic  products.  The  tourmalinization 
begins  with  the  appearance  of  needles  and  bunches  of  crystals  of 
tourmaline  traversing  fresh  quartz  grains,  as  shown  in  Fig.  23. 
These  tourmaline  crystals,  by  further  growth,  finally  replace  the 

*  Zeitschr.  d.  d.  geol.  Ges.,  Bd.  li.,  p.  433,  1899. 


544  METASOMATIC    PROCESSES   IN   FISSURE-VEINS. 

quartz  altogether.  According  to  the  description,  the  fissure- 
veins  must  have  been  produced  partly,  at  least,  by  processes  of 
filling.  Where  they  traverse  the  schists,  their  walls  show  im- 
pregnation of  ores  and  the  development  of  a  great  quantity  of 
sericite.  Sometimes,  it  should  be  added,  the  wall-rocks  are 
completely  silicified.  Of  greatest  interest  are  the  quartz-por- 
phyry dikes  and  their  alteration-products.  The  principal  sec- 
ondary mineral  in  these  dikes  is  topaz,  while  tourmaline  is 
only  of  subordinate  importance.  The  groundmass  of  the  por- 
phyry is  changed  to  aggregates  of  topaz  and  quartz.  The 
quartz  phenocrysts  are  usually  intact,  while  the  feldspars  are 
often  completely  replaced  with  cassiterite,  pyrite,  pyrrhotite, 
arsenopyrite  and  fluorite,  as  shown  in  Fig.  22.  In  the  final 
product,  the  feldspar  and  mica  have  disappeared  completely, 
the  zircon  being,  besides  quartz,  the  only  mineral  which  has 
withstood  the  metasomatic  influences.  Here  again  siderite  ap- 
pears occasionally,  seemingly  of  simultaneous  formation  with 
the  other  metasomatic  constituents.  There  is,  as  shown  by  the 
author,  a  great  similarity  between  the  metasomatic  action  in 
these  deposits  and  that  described  from  the  vicinity  of  Schneck- 
enstein,  in  Saxony,  by  Mr.  M.  Schroeder.* 

None  of  the  rocks  from  Tasmania  can  well  be  designated  as 
"  greisen  " — a  name  which  ought  to  be  reserved  for  the  granu- 
lar alteration-products  of  granite  consisting  of  quartz,  lithion- 
mica,  topaz  and  cassiterite.  Here  again,  as  at  Altenberg,  we 
find  occasionally,  seemingly  as  an  exception,  a  change  in  the 
metasomatic  processes  resulting  in  complete  silicification  of  the 
wall-rock. 

Prof.  R.  Beckf  has  discussed  the  tin-ore  deposits  from  Banca 
and  Billiton,  in  referring  to  the  work  of  Mr.  Yerbeek  on  the 
same  subject.  It  has  been  shown  by  Prof.  Cl.  Winkler  that 
many  granites  and  rocks  allied  to  hornfels  contain  a  small  amount 
(from  0.01  to  0.07  per  cent.)  of  oxide  of  tin.  This  is  not  cassit- 
erite, but  appears  to  be  chemically  combined  with  silicates, 
partially  replacing  Si02.  Sandberger  had,  indeed,  also  shown 
long  ago  the  presence  of  tin  in  certain  muscovites  from  different 
places  in  Europe.  Another  very  interesting  fact  shown  by  Mr. 

*  Erlo.euL  z.  Geol.  Sp.  Karte  des  Konigr.  Sachsen,  Leipzig,  1885,  Section 
"  Schneckenstein."  t  Zeitschr.  f.  prakt.  Geologic,  1898,  p.  121. 


METASOMATIC    PROCESSES   IN   FISSURE-VEINS.  545 

Verbeek  is  a  stanniferous  siliceous  sinter,  deposited  at  a  hot 
spring  in  Malacca.  This  sinter  contains,  according  to  an 
analysis  by  St.  Meunier,  Si02,  91.8;  Sn02,  0.5;  Fe203,  0.2,  and 
H20,  7.5  per  cent. 

This  observation  possesses  the  greatest  importance  for  our 
knowledge  of  tin-deposits,  as  it  shows  that  the  metal  may  be 
held  in  solution  and  deposited  at  ordinary  pressure  by  thermal 
waters.  Prof.  Beck  shows  the  presence  of  primary  cassiterite 
in  some  granites  from  the  same  locality,  and  also  points  out 
that  the  veins  are  practically  identical  with  tin-deposits  from 
other  parts  of  the  world,  being  characterized  by  an  often  strong 
alteration  of  the  adjoining  country-rock,  converting  it  into 
typical  greisen.  The  feldspar  is  replaced  by  topaz,  cassiterite 
and  muscovite.  The  typical  greisen  is  illustrated  in  Fig.  24, 
copied  from  Prof.  Beck's  article. 

2.  Scapolite- Apatite  Veins. 

This  interesting  group  of  veins  has  lately  been  described  in 
detail  by  Prof.  Vogt*  It  is  characterized  by  some  most  re- 
markable features,  closely  relating  it  on  one  hand  to  the  group 
of  the  cassiterite-veins,  but  showing,  on  the  other  hand,  strong 
relationships  with  the  pegmatite-veins,  formed  under  pneu- 
matolytic  conditions  and  exceedingly  high  temperature  and 
pressure.  The  structural  features  of  scapolite-apatite  veins  are 
not  those  of  fissure-veins,  as  they  chiefly  follow  contraction- 
joints  (in  gabbro).  Indeed,  this  may  be  said  to  some  extent  of 
cassiterite-veins ;  but  the  latter  often  also  follow  strong,  well- 
defined  fissures.  At  any  rate,  it  seems  probable  that  the  apatite- 
veins  were  formed  almost  simultaneously  with,  or  very  closely 
following,  the  solidification  of  the  magma. 

The  characteristic  minerals  are  apatite,  phosphates,  rutile, 
pyrrhotite,  specularite,  enstatite,  scapolite,  hornblende  and 
malacolite,  many  of  which  are  absolutely  foreign  to  ordinary 
fissure-veins.  A  most  characteristic  feature  is  the  presence  of 
chlorine  (in  apatite  and  scapolite),  just  as  fluorine  persistently 
appears  in  cassiterite-veins.  In  the  gabbro  adjoining  the  vein- 
filling,  the  labradorite  is  usually  altered  to  scapolite,  and  the 
diallage  to  hornblende.  This  alteration  is  explained  (loc.  cit., 
p.  456)  as  a  saturation  of  the  country-rock  under  high  pressure 

*  J.  H.  L.  Vogt,  Zeitschr.f.  prakt.  GeoL,  1895,  p.  367. 


546  METASOMATIC    PROCESSES    IN   FISSURE-VEINS. 

by  the  sodium  chloride  which  acted  as  a  mineralizing  agent 
during  the  formation  of  the  veins. 

3.    Tourmalinic  Gold- Copper  Veins. 

In  the  type  of  veins  distinguished  by  a  gangue  of  tourmaline 
and  quartz  the  country-rock  is  generally  subject  to  strong 
metasomatic  changes.  The  vein-forming  agents,  which  con- 
tained boron  and  some  fluorine,  appear  to  have  attacked  the 
adjoining  rock  strongly,  and  caused  a  more  or  less  complete 
metasomatic  conversion  into  tourmaline.  Yon  Groddeck*  has 
described  an  occurrence  of  this  kind  from  Tamaya,  Chile,  in 
which  veins  containing  copper-ores  cut  gabbro  and  porphyrites. 
The  tourmaline  is  here  not  only  present  in  the  filling  of  the  fis- 
sure but  is  also  distributed  through  the  adjoining  country-rock. 
A  further  contribution  to  the  knowledge  of  veins  carrying  tour- 
maline was  given  by  A.  "W.  Stelznerf  in  his  description  of  oc- 
currences of  this  kind  from  Chile.  %  The  rocks  examined,  from 
the  mining  district  of  Las  Condes,  90  miles  east  of  Santiago, 
consist  of  granite  and  greenish  porphyritic  rocks,  which  the 
author  is  inclined  to  consider  as  altered  andesites.  The  vein- 
filling  is  pyrite,  chalcopyrite,  quartz  and  a  loose  porous  mass 
of  tourmaline  needles.  By  a  specific-gravity  separation  of  the 
latter,  Stelzner  obtained,  as  a  residue,  zircon  in  well-developed 
crystals,  as  well  as  specularite  and  anatase.  The  zircon  is 
probably  developed  under  the  influence  of  the  vein-forming  so- 
lutions, the  anatase  and  specularite  quite  certainly  so.  Again 
the  fact  is  emphasized  that  the  adjoining  country-rock  is 
bleached  and  filled  with  pyrite  and  tourmaline. 

Dr.  E.  HussakJ  has  recently  described  the  auriferous  quartz- 
vein  of  Passagem,  in  Minas  Geraes,  Brazil.  This  vein,  which 
lies,  parallel  to  the  stratification,  between  mica  schist  and  itabi- 
rite  (hematite-mica-schist),  shows  a  filling  of  quartz,  tourmaline, 
and  arsenopyrite,  with  smaller  quantities  of  pyrite  a.nd  pyrrho- 
tite.  The  arsenopyrite  is  strongly  auriferous.  A  very  inter- 
esting feature  is  the  occurrence  of  zircon  and  monazite  in  the 
ore,  formed  apparently  simultaneously  with  it.  Here,  too,  the 
tourmaline  is  present  in  the  adjoining  country-rock.  Musco- 

*  Zeitschr.  d.  d.  geol.  Ges.,  39,  1887,  p.  237. 

f  Posthumously  published  in  Zeitschr.  f.  prakt.  Geologic,  1897,  p.  41. 

J  Zeitschr.  f.  prakt.  Geologic,  1898,  p.  345. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 
FlG.  1. 


547 


Silicified  Calcareous  Shale  with  Outline  of  Foraminiferal  Test.  Diadem  lode, 
Plumas  county,  Cal.  ( After  H.  W.  Turner. )  Crossed  nicols.  All  quartz.  Mag- 
nified 29  diameters. 

FIG.  2. 


Primary  Vein  Quartz  from  Filling.       Federal  Loan  mine,  Nevada  county,  Cal. 
Crossed  nicols.     All  Quartz.     Magnified  14  diameters. 
35 


548 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 
FIG.  3. 


Incipient  Silicification  of  Limestone.     Aspen,  Colo.     White  areas  represent  quartz 
crystals  with  small  inclusions  of  limestone.     Magnified  30  diameters. 

FIG.  4. 


Silicified  Limestone  ( "  Jasperoid " ) .     Aspen,  Colo.     Crossed  nicols.     All  quartz. 
Small  inclusions  of  calcite  in  some  of  the  grains.     Magnified  30  diameters. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 
FIG.  5. 


549 


Incipient  Silicification  of  Orthoclase  Crystal  in  Rhyolite.  Silver  City,  Idaho. 
Crossed  nicols.  a,  Orthoclase  ;  b,  secondary  quartz  ;  c,  sericite.  Magnified  34 
diameters. 

FIG.  6. 


Hornblende  Crystal  with  Partial  Chloritization  and  Silicification  ;  in  Propylitic 
Andesite.  Virginia  City,  Nevada.  (After  G.  F.  Becker. )  White,  quartz  and 
calcite  ;  grey,  chlorite  ;  dark  grey,  hornblende.  Magnified  70  diameters. 


FIG.  7. 


Veinlet  of  Quartz  (b)  on  Chloritized  Basalt  (a),  Keplacing  Silicified  Ehyolite  (c). 
Bishop  vein,  Silver  City,  Idaho.     Magnified  11  diameters. 


550  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

FIG.  8. 


Filled  Veinlet  in  Andesite  Breccia.  Independence  mine,  Cripple  Creek,  Colo. 
q,  Quartz  ;  o,  valencianite  (orthoclase)  ;  p,  pyrite ;  /,  fluorite  ;  g,  ground-mass 
of  breccia.  Fluorite  and  pyrite  partly  replacing  ground -mass.  Magnified  11 
diameters. 


FIG.  9. 


Fluorite  Ore,  Keplacing  Phonolite.     Portland  mine,  Cripple  Creek,  Colo,     p,  Py- 
rite ;  q,  quartz,  coarser  and  finer  grains  ;  /,  fluorite.    Magnified  50  diameters. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 
FIG.  10. 


551 


Orthoclase  Grain  (o)  in  Granite  Andesite  Breccia,  Partly  Replaced  by  Quartz  (q)  • 
Fluorite  (/);  Pyrite  (p]  ;  Sericite  (a)  ;  Ground-Mass  of  Breccia  (51).  Inde- 
pendence mine,  Cripple  Creek,  Colo.  Magnified  60  diameters. 

FIG.  11. 


Filled  Space  of  Dissolution  in  Granite.  ' '  G  ranite  Ore, ' '  Independence  mine,  Crip- 
ple Creek,  Colo,  o,  Orthoclase  of  granite  ;  m,  biotite,  converted  into  valen- 
cianite and  pyrite  ;  v,  valencianite  (secondary  orthoclase), showing crustification; 
q,  quartz.  Magnified  20  diameters. 


552 


METASOMATIC    PROCESSES    IN    FISSUKE-VEINS. 
FIG.  12. 


Andesine  Crystal  in  Granodiorite,  Replaced  by  Sericite  and  Calcite.  Pinetree 
vein,  Ophir,  Placer  county,  Cal.  q,  Quartz  ;  m,  muscovite  ;  c,  calcite  ;  s.  seri- 
cite.  Magnified  80  diameters. 


FIG.  13. 


Quartz  Grain  in  Same  Section,  Partly  Replaced  by  Calcite.  q,  Quartz  ;  c,  calcite 
with  some  sericite  replacing  from  outside  ;  also,  secondary  calcite  grains  form- 
ing on  inclined  fissure- plane  in  quartz.  Magnified  80  diameters. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  553 

FIG.   14. 


Fluorite  Eeplacing  Limestone.     Florence  mine,  Judith  Mountains,  Mont.    /,  Flu- 
orite  ;  /,  limestone  ;  </,  secondary  quartz.     Magnified  7  diameters. 


FIG.  15. 


Metasomatic  Emplacement  of  Quartz  in  Granodiorite  by  Calcite  and  Sericite. 
Providence  mine,  Nevada  City,  Cal.  White  areas  quartz.  Shaded  areas  fine- 
grained calcite  with  some  sericite.  Magnified  52  diameters. 


554 


METASOMATIC    PROCESSES    IN    FISSURE- VEINS. 
FIG.   16. 


JLX 


*  «  '  fC~~r\/  \  .1  i-'  «r>  -.  v  ^-5 

'      *-~\V       >v'-      £    -    ^      —v/ 

^-^1-     4  yA^* 
/^  W^1*  -- 

•<v^<  >x->* ••^"•-w 

_v   <>-        >^>-^     \^F         i 

Jj-^C^>>.;'  ••••* 
^^.f>c^\-> 

S    •*  s.        '%       /        L'1  ^r 

<^5^  ,  -:\^L ^7. 


<& 


&> 


Siderite  with  Pyrite  and  Galena,  Eeplacing  Quartzite.  Helena  and  Frisco  mine, 
Cceur  d'Alene,  Idaho,  q,  Quartz  grains  ;  *,  sericite  ;  si,  siderite  ;  black,  galena 
and  pyrite.  Magnified  100  diameters. 


FIG.  17. 


^—^^ 

Keplaced  Quartzite,  Same  Locality  as  Fig.  16.  Black,  galena  ;  2,  zinc-blende  ;  q, 
quartz  ;  s,  sericite ;  si,  granular  siderite.  Quartzite  in  same  section  gradually 
changing  to  this  ore.  Magnified  35  diameters. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 
FIG.   18. 


555 


Quartzite  Partly  Eeplaced  by  Siderite  and  Pyrite.  Helena  and  Frisco  mine, 
Coeur  d'  Alene,  Idaho,  q,  Quartz  grains  ;  s,  sericite ;  si,  siderite  with  partly 
rhombohedral  form  ;  black,  pyrite.  Magnified  100  diameters. 


FIG.  19. 


Orthoclase  Partially  Replaced  by  Muscovite  and  Kaolinite.  From  quartz-monzo- 
nite  adjoining  recent  vein,  Boulder,  Mont,  o,  Orthoclase ;  q,  quartz  ;  w,  mus- 
covite  ;  k.  kaolinite.  Magnified  22  diameters. 


556  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

FIG.  20. 


Part  of  Andalusite  Crystal  Altered  into  Muscovite,  Arsenopyrite,  etc.  Passagem 
gold-quartz  vein,  Brazil.  (After  E.  Hussak. )  J/,  Pyrrhotite  ;  A,  arsenopyrite; 
P,  pyrite ;  Qu,  quartz  ;  R,  rutile  ;  Mu,  muscovite  ;  T,  tourmaline. 


FIG.  21. 


Replacement- Veinlet  of  Tourmaline  in  Fresh  Andesine  Grain.  Keystone  mine, 
Meadow  Lake,  Nevada  county,  Cal.  t,  Tourmaline  ;  /,  andesine  ;  e,  epidote; 
s,  sericite.  Magnified  50  diameters. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 
FiG.  22. 


557 


Feldspar  Crystal  Keplaced  by  Topaz,  Quartz,  Fluorite  and  Cassiterite,  in  Ground- 
Mass  Converted  to  Partly  Radial  Aggregates  of  Topaz.  Mount  Bischoff,  Tas- 
mania. (After  W.  von  Fircks.) 


FIG.  23. 


Incipient  Tourmalinization  of  Quartzite.  Three  quartz  grains  shown.  Needles 
single  and  in  bunches,  of  tourmaline.  Mount  Bischoff,  Tasmania.  (After  W. 
von  Fircks. ) 


558 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 


"Greisen"  from  Tin-Deposits  of  Banca,  Malay  Peninsula.  Derived  from  gran- 
ite. (After  K.  Beck.)  </,  Lithion-mica ;  q,  quartz;  z,  cassiterite ;  t,  topaz. 
Stippled  spots  in  mica  consist  of  zircons  and  rutiles,  surrounded  by  polychroic 
ring.  Slightly  magnified. 

FIG.  25. 


Altered  Quartz-Mica-Diorite.  Croesus  mine,  Wood  Kiver,  Idaho,  a,  Galena;  b, 
arsenopyrite  ;  c,  chalcopyrite ;  d,  sericite  ;  e,  quartz  with  secondary  fluid  inclu- 
sions ;  /,  rutile ;  g,  chlorite.  Magnified  19 \  diameters. 


FIG.  26. 


Altered  Serpentine.     Idaho  mine,  Grass  Valley,  Cal.     m,  Magnesite  ;  s,  serpen- 
tine ;  p,  pyrite  ;  </,  fine  granular  quartz.      Magnified  15  diameters. 


FIG.  27. 


Altered  Granodiorite.  Bellefountain  mine,  Nevada  City,  Cal.  m,  Fine  aggregate 
of  sericite,  with  a  little  calcite  and  secondary  quartz,  replacing  orthoclase  and 
andesine  ;  6,  original  biotite  altered  to  sericite  ;  q,  original  quartz  ;  black,  pyrite 
with  included  sericite.  Magnified  15  diameters.  (559) 


560  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

FiG.  28. 


Emplacement- Vein  in  Syenite  Eock.  War  Eagle  mine,  Eossland,  British  Colum- 
bia, a,  Granular  aggregate  of  orthoclase  witli  very  little  sericite ;  black,  sec- 
ondary pyrrhotite ;  6,  secondary  biotite ;  q,  secondary  quartz ;  c,  chlorite. 
Magnified  60  diameters. 

FIG.  29. 


Galena,  Eeplacing  Crystalline  Limestone.  Elkhorn  mine,  Montana,  g,  Galena  ; 
p,  pyrite ;  c,  calcite  grains  of  limestone;  g,  secondary  quartz.  Magnified  15 
diameters. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 


561 


FIG.  30. 


Quartzite  Showing  Filled  Quartz  Veinlet  and  Accompanying  Galena,  Eeplacing 
the  Quartzite  on  One  Side  of  the  Filled  Fissure.  The  quartzite  contains  some 
replacing  siderite.  Bunker  Hill  and  Sullivan  mine,  Coeur  d'Alene,  Idaho. 
Black,  galena ;  white,  quartz  ;  grey,  quartzite.  Natural  size.  Reproduced 
from  photograph. 


562  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

vite  or  sericite  is  also  described  as  very  plentiful  in  the  schis- 
tose rock  adjoining  the  vein.  Certain  crystals  of  andalusite, 
occurring  (as  inclusions  ?)  in  the  vein,  are  completely  altered 
into  sericite,  rutile,  arsenopyrite  and  pyrite,  as  is  well  shown  in 
Fig.  20  (reproduced  from  Dr.  Hussak's  paper).  The  author 
concludes  from  his  study  that  the  deposit  is  a  product  of  igne- 
ous injection,  and  should  be  considered  a  dike  rather  than  a 
fissure-vein,  basing  this  conclusion  largely  on  the  occurrence  of 
zircon,  monazite,  tourmaline  and  staurolite  in  the  adjoining 
rock.  It  is  a  question  whether  this  argument  will  carry  con- 
viction. From  Dr.  Hussak's  excellent  descriptions  I  should  be 
inclined  to  consider  this  interesting  occurrence  as  a  fissure-vein 
deposited  by  aqueous  agencies,  though,  perhaps,  at  a  higher 
temperature  than  ordinary  veins.  The  contact-minerals  cited 
by  the  author  do  not  appear  to  be  confined  to  the  adjoining 
rock,  but  are  present  in  the  whole  series  of  schists.  The  very 
schistose  and  sericitic  quartzite  forming  the  wall  of  the  vein, 
and  the  presence  of  pseudomorphic  sericite  after  andalusite,  as 
well  as  the  apparently  simultaneous  forming  of  arsenopyrite 
and  sericite,  appear  to  me  evidence  that  the  deposit  of  Passagem 
is  really  a  normal  vein.  The  tourmaline  is  here  also  present  in 
the  country-rock,  apparently  replacing  it  to  a  greater  or  lesser 
degree. 

Again,  similar  deposits  have  been  described  from  Meadow 
Lake,  Nevada  county,  Cal.,*  where  granitic  and  dioritic  rocks 
contain  fissure-veins  with  pyrite,  arsenopyrite,  pyrrhotite,  zinc- 
blende,  and  various  secondary  copper-ores,  indicating  primary 
chalcopyrite  in  a  gangue  of  quartz  and  tourmaline,  with  which 
some  yellow  epidote  is  usually  associated.  Chlorite  is  also 
common  in  the  gangue  as  well  as  a  brown  mica,  probably  biotite. 
A  colorless  mica  and  a  little  calcite  were  also  observed.  In  con- 
trast to  the  usually  clearly  defined  fissure-veins  of  the  gold-belt 
of  California,  in  which  the  quartz-filling  is  the  predominant  ore, 
these  veins  show  very  irregular  and  undefined  walls,  and  it  is 
clear  that  the  mineral-forming  solutions  rose  along  very  narrow 
fissures,  from  which  they  penetrated  more  or  less  deeply  into 
the  adjoining  country -rock,  and  there,  by  metasomatic  replace- 
ment deposited  the  auriferous  ores.  One  of  these  occurrences 

*  Waldemar  Lindgren,  Am.  Jour,  of  Sci.,  3d  series,  vol.  xlvi.,  Sept.,  1893,  p.  201. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  563 

is  illustrated  in  Fig.  21.  The  specimen  is  from  the  Keystone 
mine,  and  shows  a  granitic  rock  traversed  by  a  narrow  fissure, 
from  which  an  intense  alteration  has  proceeded,  converting  the 
immediate  rock  into  an  aggregate  of  quartz  and  tourmaline. 
The  metasomatic  process  is  well  shown  in  the  figure. 

Prof.  Yogt  describes*  certain  veins  in  Telemarken,  Norway, 
which  he  considers  as  related  to  the  cassiterite-veins  proper. 
These  contain  chalcopyrite,  bornite,  and  chalcocite,  also  a  little 
native  silver  and  gold,  all  associated  with  a  gangue  of  fluorite, 
tourmaline,  apatite,  muscovite  and  calcite.  They  are  con- 
sidered to  be  genetically  connected  with  the  granite  in  which 
they  appear,  and  the  presence  of  tourmaline  and  apatite  cer- 
tainly suggests  their  close  relationship  to  normal  cassiterite- 
veins.  The  country-rock  is  a  normal  biotite-granite,  with  or- 
thoclase,  microcline  and  oligoclase,  and  no  muscovite.  The 
alteration  extends  for  several  feet  on  both  sides  of  the  veins, 
and  all  transitions  are  plainly  visible.  The  first  part  of  the  pro- 
cess consists  in  a  peripheric  change  of  biotite  to  muscovite  and 
a  little  epidote ;  then  the  feldspars  are  attacked,  muscovite  and 
quartz  together  with  a  little  calcite  forming  on  the  cleavage- 
planes  ;  and  finally  the  feldspars  and  biotite  are  entirely  decom- 
posed. The  result  is  muscovite,  quartz,  calcite,  rutile,  zircon 
and  apatite, — the  latter  two  not  altered,  but  constituting  the 
only  material  remaining  fresh  from  the  unaltered  rock.  A 
little  fluorite,  chalcopyrite  or  bornite  is  also  occasionally  pres- 
ent in  the  product  of  alteration.  Regarded  from  a  chemical 
standpoint  the  process  is  not  always  the  same.  Sometimes,  ac- 
cording to  Vogt,  substance  is  added ;  sometimes  taken  away. 
Quartz  may  occasionally  prevail ;  at  other  places  muscovite  pre- 
dominates. Prof.  Yogt  calls  this  altered  rock  a  greisen ;  but 
the  process  of  alteration  as  described  by  him  is  so  nearly  that 
of  ordinary  sericitic  replacement  that  it  may  be  questionable 
whether  it  would  not  be  better  to  reserve  the  term  greisen  for 
the  characteristic  rock  accompanying  the  cassiterite-veins. 
The  process  of  formation  in  the  case  of  the  Telemarken  veins 
was  probably  not  carried  on  under  the  extreme  conditions 
attending  the  normal  cassiterite-veins. 

The  three  classes  of  veins  described  above  are  undoubtedly 

*  Zeitschr.f.prakt.  Geol,  1895,  p.  147. 
36 


564  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

closely  related  and  form  a  group,  which,  however,  is  connected 
by  transitions  from  the  following  classes.  In  their  whole  de- 
velopment a  distinct  genetic  connection  with  intrusive  rocks  is 
recognizable,  and  they  seem  to  have  been  formed  under  excep- 
tionally high  pressure  and  temperature — in  fact,  partly  under 
pneumatolytic  conditions.  The  metasomatic  action  on  the 
country-rock  is  very  strong,  and  the  presence  of  fluorine,  chlor- 
ine or  boron  is  characteristic.  It  is  well  to  emphasize,  how- 
ever, that  fluorine  and  boron  appear  in  many  other  veins  \vhich 
certainly  have  not  originated  under  pneumatolytic  conditions, 
or  even  under  high  temperature  or  pressure.  The  three  fore- 
going classes  appear  to  form  a  transition  from  pegmatite-veins 
to  ordinary-fissure  veins. 

4.  Biotitic  Gold-Copper  Veins. 

This  class,  of  which  few  representatives  are  thus  far  known, 
are  exemplified  in  the  veins  of  Rossland,  British  Columbia. 
They  are  well-marked  fissure-veins,  contained  in  granular,  in- 
trusive rocks  of  great  variety,  ranging  from  diorites  to  mpn- 
zonites  and  even  syenites.  The  ore-minerals  are  pyrrhotite, 
chalcopyrite  and  a  little  arsenopyrite,  all  containing  gold,  but 
usually  not  in  a  free  state,  amenable  to  amalgamation ;  the 
principal  gangue-mineral  is  biotite,  with  a  little  quartz,  calcite, 
muscovite,  amphibole,  chlorite,  tourmaline  and  garnet. 

The  veins  are  excellent  examples  of  replacement-deposits,  as 
there  is  but  little  material  which  can  be  identified  as  the  filling 
of  open  cavities,  while  most  of  the  ore  has  been  formed  by  re- 
placement of  the  rock-forming  minerals  on  both  sides  of  nar- 
row fissures.  The  original  hornblende  of  the  rock  is  altered  to 
aggregates  of  biotite  foils,  which  also  invade  the  feldspars ;  and 
simultaneously  the  feldspar  substance  is  replaced  from  small 
cracks  by  pyrrhotite  and  chalcopyrite,  forming  a  characteristic 
network  which,  by  gradual  extension,  finally  replaces  the  whole 
rock.  One  of  these  replacement-veinlets  is  illustrated  in  Fig. 
28.  The  sulphides  do  not  as  a  whole  have  crystalline  outlines, 
though  in  some  places  the  grains  show  crystal-faces.  The  sec- 
ondary character  of  the  sulphides  is  further  shown  by  narrow 
linings  of  quartz,  chlorite  or  biotite.  The  feldspar  substance,  gen- 
erally clouded  by  interpositions  of  biotite,  muscovite,  etc.,  usually 
presents  a  narrow,  clear  rim  adjoining  the  sulphides.  Exten- 


METASOMATIC    PROCESSES   IN   FISSURE-VEINS.  565 

sive  biotitization  results  in  fine-grained  siliceous  rocks,  consist- 
ing of  brown  mica  and  quartz,  possibly  also  secondary  feld- 
spars. Green  secondary  amphibole  was  noted  in  places,  em- 
bedded in  calcite.  The  whole  process  is  more  characteristic  of 
dynamic  metamorphism  than  of  ordinary  fissure-veins,  and  it 
is  probable  that  the  veins  were  formed  under  actual  unrelaxing 
compression.  Strongly  reducing  conditions  are  indicated 
(otherwise  pyrrhotite  would  not  form  so  exclusively),  and  the 
absence  of  notable  quantities  of  carbon-dioxide.  Along  sec- 
ondary slips,  below  the  water-level,  the  pyrrhotite  may  be  trans- 
formed to  pyrite.  Epidote  appears  to  be  absent.  The  veins 
are  earlier  than  an  extensive  system  of  lamprophyric  dikes 
which  cut  across  them.  These  dikes  were  no  doubt  closely 
connected  with  the  principal  intrusion  of  igneous  rock ;  and  the 
conclusion  may  be  drawn  that  the  mineralization  followed 
pretty  closely  upon  the  consolidation  of  the  rock. 

5.  Propylitic  Gold-  and  Silver- Veins. 

General  Features. — As  the  cassiterite-veins  are  closely  con- 
nected genetically  with  certain  intrusive  rocks,  so  another 
group  of  veins  shows  a  dependence  on  tertiary  effusive  rocks, 
such  as  andesites,  dacites  and  basalts,  in  part  also  rhyolites  and 
trachytes.  In  the  vicinity  of  these  veins  there  is  a  very  exten- 
sive metasomatic  action  resulting  in  so-called  propylite  (named 
by  v.  Richthofen)  which  was  regarded  formerly  as  a  primary 
rock-type,  just  as  greisen  has  sometimes  been  regarded  as  a 
primary  rock  forming  a  variety  of  granite.  But  all  fissure- 
veins  in  tertiary  effusive  rocks  do  not  belong  to  this  class ;  a 
considerable  number  belong  under  the  head  of  sericitic  veins. 
Rosenbusch  expresses  the  process  in  the  following  apt  words:* 

"  The  characteristic  features  of  the  propylitic  fades  consists  in  the  loss  of  the 
glassy  habit  of  the  feldspars  ;  in  the  chloritic  alteration  of  the  hornblende,  biotite 
and  pyroxene  (often  with  an  intermediate  stage  of  uralite),  with  simultaneous 
development  of  epidote  ;  further,  in  alteration  of  the  normal  ground-mass  into 
holocrystalline  granular  aggregates  of  feldspar,  quartz,  chlorite,  epidote  and  cal- 
cite, and  in  a  considerable  development  of  sulphides"  [usually  pyrite]. f 

*  Elemente  der  Gesteinslehre,  Stuttgart,  1898,  p.  303. 

f  Kosenbusch  adds  (loc.  eit.  and  Mikr.  Phys.  d.  Mass.  Gest.,  Stuttgart,  1896,  p. 
91)  that  similar  rocks  (excepting  the  pyrite)  may  result  from  atmospheric 
weathering.  Against  this  statement  I  would  protest,  referring  to  page  586  of 
this  paper. 


566  METASOMATIC    PROCESSES   IN   FISSURE-VEINS. 

Chemically,  the  change  is  not  considerable ;  the  principal 
additions  consist  of  water  and  sulphur ;  some  substance  is  often 
subtracted,  usually  lime  or  magnesia,  while  the  alkalies  show 
slight  change.  The  following  analysis,  taken  from  Mr.  Clar- 
ence King's  monograph  on  the  Comstock  Lode,  shows  the 
composition  of  a  propylitic  andesite : 

Per  cent. 

SiO2,  .         .         .         .  ,         ......  .  .  64.62 

A12O3>  .,'..,  ,        .        ,         .  .  .  11.70 

FeO,  .    '•-.'•    .        .  .        .        ;      •';  .  .  8.39 

MgO,  .       -.    .'    .    •    «  .    ••'  .>.-.-'    «        .  .  .  1.18 

CaO,  .        .        .        .  .        f        *    .  ,.  •  •  8.96 

Na2O,  ....  V      .        .        .  .'  .  3.13 

K2O,  .         ...  .        ,        .        .  .  .  1.95 

H2O,  .        .        .        .  .        *:       .        .  .  .  1.02 

100.95 

Propylitic  rocks  occur  in  the  vicinity  of  large  fissure-veins 
and  vein-systems  in  Tertiary  effusive  rocks — for  instance,  at  the 
Comstock,  Nevada ;  Pachuca  and  Real  del  Monte,  Mexico ;  in 
the  South  American  Andes;  and  in  Hungary  and  Transyl- 
vania. Although  the  propylite  indicates  the  general  metaso- 
matic  process  in  these  veins,  it  is  not  uncommon  to  find  rocks 
and  soft  clays  containing  sericite  as  a  product  of  the  extreme  me- 
tasomatic  action  very  close  to  the  vein.  The  waters  principally 
active  during  the  formation  of  the  propylitic  veins  probably 
contained  only  a  small  amount  of  carbon  dioxide  and  very 
little  lime,  but  may  have  been  rich  in  sulphuretted  hydrogen. 

The  filling  of  open  spaces  is  a  very  important  process  in 
these  veins,  as  may  be  expected  from  their  formation  compara- 
tively near  the  surface ;  and  this  filling  usually  constitutes  the 
principal  ore,  though  altered  rock,  containing  enough  gold  and 
silver  to  be  classed  as  ore,  occurs  extensively  in  many  places. 

The  primary  character  of  propylite  as  a  separate  eruption 
is  to  some  extent  still  upheld  by  Zirkel,*  but  his  arguments  are 
not  convincing. 

The  Comstock  Lode. — The  relations  at  the  Comstock  lode, 
described  by  G.  F.  Becker,  f  are  exceedingly  interesting,  be- 
cause the  deposit,  besides  being  celebrated  for  its  immense 

*  Lehrbuch  der  Petrographie,  ii.,  p.  485. 

f  G.  F.  Becker,  "Geology  of  the  Comstock  Lode,"  Monograph 2IL,  U.  S.  Geol. 
Surv. 


METASOMATIC    PROCESSES   IN   FISSURE-VEINS.  567 

production,  is  a  representative  type.  The  vein,  which  carries 
both  silver  and  gold,  is  surrounded  by  an  area  of  extreme 
alteration,  occupying  a  space  of  about  5  by  2  miles,  affecting 
alike  the  diorite,  diabase  and  andesite.*  In  the  course  of  this 
alteration  the  hornblende  and  augite  are  changed  to  chlorite, 
which  also  infiltrates  the  feldspars.  Pyrite  is  present  in  the 
rock  in  proportion  to  its  alteration,  and  is  probably  developed 
from  the  ferro-magnesian  silicates ;  to  a  lesser  degree,  from  the 
magnetite.  The  feldspars  are  decidedly  less  easily  altered  than 
the  silicates  mentioned.  Beginning  alteration  is  made  appar- 
ent by  specks  of  calcite.  Later  on,  quartz  grains  and  an  opaque 
white,  doubtful  substance  appears.  ~No  kaolinite  was  recog-; 
nized,  and  if  present,  it  occurs  in  very  subordinate  quantities 
only.  Epidote  is  more  abundant  near  the  surface  than  in  depth, 
and  appears  to  result  from  the  further  alteration  of  chlorite, 
under  the  influence  of  calcic  solutions  derived  from  the  feldspars. 
Muscovite  as  a  product  of  alteration  of  the  feldspars  is  absent. 

The  extreme  alteration  is  represented  by  the  so-called  clays, 
which  were  formerly  supposed  to  consist  largely  of  kaolin. 
Becker  shows  this  assumption  to  be  erroneous,  and  gives  anal- 
yses to  show  that  the  clays  are  simply  derived  from  the  normal 
rocks  by  a  partial  alteration.  An  examination  of  the  analyses 
quoted  from  the  monograph  of  Clarence  King,f  in  Table  I., 
following  page  152  of  Becker's  monograph,  will  show  that  in 
the  diorites,  andesites  and  diabases  the  N"a2O  decidedly  exceeds 
the  K20.  In  two  of  the  three  analyses  of"  propylites,"  which 
are  simply  rocks  subjected  to  incipient  thermal  alteration,  the 
K20  is  present  in  decidedly  larger  quantity  than  the  Na20.  In 
the  remaining  u  propylite  "  analysis,  the  reverse  is  true.  The 
four  analyses  of  the  "  clays,"  or  the  extremely  altered,  crushed 
and  bleached  material  adjoining  the  veins,  run  as  shown  in 
table  on  the  following  page. 

The  quantitative  relations  of  the  alkalies  clearly  show  a  con- 
centration of  potash  and  a  leaching  of  soda.  There  can 
scarcely  be  any  doubt  that  these  clays  really  consist  of  30  to 
40  per  cent,  of  finely  divided  sericite,  mixed  with  some  quartz 
and  residual  rock. 

*  Without  wishing  to  reopen  the  Comstock  question,  I  would  state  my  strong 
belief  that  these  three  rocks  are  separate  and  independent  eruptive  bodies. 
t  "Survey  of  the  40th  Parallel,"  vols.  i.,  iii.,  vi.,  passim. 


568  METASOMATIC    PROCESSES   IN    FISSURE-VEINS. 

Analyses  of  Comstock  Clays. 


I. 

II. 

III. 

IV. 

SiO,... 

Per  cent. 
60  02 

Per  cent. 
59  71 

Per  cent. 
65.  69 

Per  cent. 
39  52 

TiO2  

ALOo 

12  15 

17  59 

15  39 

15  97 

FeA 

4  38 

5  04 

2  11 

4  47 

Feo  !.:::::::::: 

MnO  

CaO 

6  00 

0  73 

1  66 

9  20 

MgO  

1.40 

4.41 

2.85 

3.40 

Na2O  

0.45 

1.01 

2.36 

K2O  

1.23 

3.98 

4.64 

3.11 

CO9.. 

3.17 

6.20 

FeS2  

1.84 

3.58 

2.84 

9.18 

P,(X.  . 

0.34 

trace 

trace 

trace 

H20.... 

8.09 

4.19* 

2.80* 

9.95 

Total 

99.07 

100.24 

100.34 

101.00 

Locality. 

I.  Yellow  Jacket  east  clay, 
II.  Chollar  west  clay,  . 

III.  Hale  and  Norcross  east  clay, 

IV.  Savage  second  station,   . 


Analyst. 

S.  W.  Johnson. 
W.  G.  Mixter. 
W.  G.  Mixter. 
S.  W.  Johnson. 


The  Veins  of  Nagydg,  Hungary. — In  1885,  Bela  von  Inkey 
published  an  interesting  report  on  the  ore-deposits  at  Na- 
gyag.f  These  consist,  in  brief,  of  a  complicated  system  of 
not  very  persistent  veins,  cutting  an  eruptive  mass  of  tra- 
chytic  rocks  breaking  through  Tertiary  sediments,  which  in 
turn  rest  on  older  argillites.  The  deposits  are  famous  as  con- 
taining gold  accompanied  by  various  interesting  tellurides. 
The  whole  occurrence  bears  in  its  geological  relation  some 
similarity  to  the  deposits  at  Cripple  Creek,  Colo.  The  principal 
gangue  is  quartz,  accompanied  by  galena,  zinc-blende,  pyrite, 
chalcopyrite,  etc.,  besides  gold  and  rich  tellurides.  In  addition 
to  the  quartz,  various  carbonates  are  present.  The  fissures  are 
small,  but  contain  the  (generally  rich)  ore  as  the  filling  of  open 
spaces.  The  sedimentary  rocks  do  not  in  general  contain 
much  valuable  ore,  although  such  occurrences  are  known.  The 
ore-shoots  are  chiefly  confined  to  the  eruptive  mass  of  trachyte. 
In  the  vicinity  of  the  mineral  deposits  the  trachytes  are  quite 
generally  changed  to  so-called  propylitic  rocks,  the  change 


*  By  ignition. 

f  Nagydg  und  seine  Erzlagerstatten,  by  Bela  von  Inkey,  Budapest,  1885. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  569 

consisting  in  the  development  of  chlorite  in  the  ferro-magne- 
sian  minerals.  It  is,  in  fact,  difficult  to  obtain  fresh  rocks 
anywhere  in  the  vicinity.  In  the  immediate  vicinity  of  the 
veins,  and  in  the  whole  zone  in  which  the  veins  are  closely 
massed,  the  rock  has  suffered  another  alteration,  which  v.  Inkey 
refers  to  as  a  kaolinization,  in  consequence  of  which  the  rock 
loses  its  normal  hardness  and  greyish  or  greenish  color,  and  is 
transformed  into  a  soft  brownish  yellow  to  white  mass,  resem- 
bling kaolin.  The  last  traces  of  hornblende  and  augite  are 
lost,  and  only  carbonates  replace  them.  The  biotite  is  trans- 
formed to  a  soft  talcose  substance.  The  magnetite  is  often 
replaced  by  pyrite.  Only  the  quartz  remains  unaltered,  and, 
in  connection  with  the  pseudomorphs  of  biotite,  affords  the 
best  criterion  for  recognizing  the  trachytic  nature  of  this 
highly  altered  rock.  This  modification  is  so  clearly  connected 
with  the  veins  that  its  origin  from  the  fissures  cannot  be  doubted. 
Where  the  rock  is  not  altered,  rich  shoots  are  rarely  found. 
Yon  Inkey  thinks  that  this  alteration  clearly  indicates,  not 
superficial  waters,  but  thermal  waters  ascending  on  the  fissures. 
Both  kinds  of  alteration,  the  chloritic  as  well  as  the  "  kaolin- 
itic,"  are  regarded  as  closely  related  to  the  genesis  of  the  veins. 
The  chloritic  modification  is  supposed  to  have  resulted  from  a 
sort  of  hydrometamorphic  action  preceding  the  immediate 
formation  of  the  veins.  This  so-called  kaolinized  rock  has 
been  examined  in  more  detail  by  Dr.  Kollbeck,*  who  showed 
it  consists  partly  of  sericite.  Dr.  Kollbeck  separated  the  rock 
by  means  of  heavy  solutions,  finding  that,  besides  the  sericite, 
it  contained  some  pyrite  (with  a  little  arsenic,  gold  and  silver), 
zircon  and  anatase,  as  well  as  a  little  apatite.  The  chief  con- 
stituent fell  between  specific  gravity  2.918  and  2.649,  though 
most  of  it  came  down  at  2.788.  The  analysis  of  the  micaceous 
mineral  gave  the  following  composition:  Si02,  48.67;  A1203, 
39.30;  Fe203,  0.30;  MnO,  0.25;  CaO,  0.38;  MgO,  1.42;  K20, 
3.73;  Na20,  0.13;  H20,  5.83;  CO2,  0.23;  FeS2,  0.43;  total, 
100.67  per  cent. 

As  may  be  inferred  from  the  variability  of  the  specific 
gravity,  the  mineral  is  clearly  not  pure  muscovite,  but  probably 
a  mixture  of  sericite  and  kaolinite,  as  is  shown  by  the  high 

*  Oesterr.  Zeitschr.f.  B.  &  H.-Wesen,  1888,  pp.  25-27. 


570  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

percentage  of  alumina  and  water  and  the  low  percentage  of 
potassa. 

Pachuca,  Mexico. — Another  type  of  this  class  of  veins  is  de- 
scribed by  Messrs.  J.  Aguilera  and  E.  Ordonez.*  The  well- 
known  and  very  productive  veins  of  Pachuca  cut  a  series  of 
Tertiary  effusive  rocks,  principal  among  which  is  a  pyroxene- 
andesite.  Rhyolite  and  basalt  are  also  present,  but  contain, 
near  Pachuca,  no  mineral  veins.  The  deposits  are  typical  fis- 
sure-veins, filled  with  a  gangue  of  quartz  carrying  in  fine  dis- 
semination argentite,  pyrite,  galena,  zinc-blende,  stephanite  and 
polybasite.  The  value  is  almost  exclusively  in  silver,  very  little 
gold  occurring.  There  is  no  ruby-silver;  and  in  depth  the 
veins  are  said  to  be  impoverished  by  the  appearance  of  large 
quantities  of  barren  zinc-blende.  The  pyrite  and  galena  con- 
tain a  little  silver,  but  no  gold.  Calcite  appears  in  subordinate 
and  varying  quantities,  as  the  latest  gangue,  filling  interstices 
between  quartz  crusts.  Inclusions  of  country-rock  in  sharp 
fragments  are  common  in  the  quartz.  On  the  whole,  there 
can  be  no  doubt  that  the  ore  in  these  veins  is  chiefly  the  fill- 
ing of  open  cavities  by  quartz,  as  in  the  gold-quartz  veins  of 
California. 

Over  a  large  area  in  the  vicinity  of  the  veins  the  rocks  con- 
tain much  chlorite  and  quartz,  with  a  little  calcite.  Close  to 
the  veins,  the  alteration  is  most  intense.  The  country-rock  is 
filled  with  small,  perfect  crystals  of  pyrite,  which  is  always 
practically  barren.  Its  sharply  developed  crystal-form  contrasts 
with  the  generally  anhedral  form  of  the  pyrite  in  the  vein. 
Black  sulphides  occasionally,  but  rarely,  appear  in  the  country- 
rock  next  to  the  veins.  These  are,  of  course,  rich.  The  rocks 
immediately  adjoining  the  veins  contain,  besides  pyrite,  much 
chlorite,  also  some  calcite  and  a  considerable  amount  of  second- 
ary quartz.  The  latter  is  so  abundant  that  the  chief  alteration 
near  the  vein  is  often  a  silicification,  the  quartz  sometimes  ap- 
pearing in  the  ground-mass ;  in  other  cases  the  whole  rock  is 
silicified  by  substitution  of  quartz.  Chalcedony,  and  more 
rarely  opal,  is  also  found  in  the  altered  rock.  In  many  cases, 
in  the  deeper  parts  of  the  veins,  the  only  difference  between 
the  rocks  adjoining  and  those  more  distant  from  the  vein  is  in 

*  Boletin  del  Instit.  Geol.  de  Mexico,  Nos.  7,  8,  9.     "  El  Mineral  de  Pachuca." 


METASOMATIC    PROCESSES    IN  .  FISSURE-VEINS.  571 

the  quantity  of  impregnating  silica.  The  pyroxene  alters  to 
chlorite  and  epidote.  The  feldspars  (oligoclase  and  labradorite) 
are  often  converted  to  calcite,  epidote  and  quartz.  Mr.  Ordonez 
says  further  that  the  feldspars  have  a  marked  tendency  to  be- 
come transformed  into  kaolinite  (arcilld).  As  he  gives  no  anal- 
yses of  the  altered  rocks,  it  is  difficult  to  judge  whether  finely 
divided  sericite  is  present  or  not.  On  the  whole,  the  similarity 
of  this  district  to  the  Comstock,  so  far  as  the  alteration  is 
concerned,  is  very  striking ;  and  there  is  little  doubt  that  the 
two  deposits  owe  their  origin  to  extremely  similar  solutions. 

New  Zealand. — The  auriferous  veins  of  Thames,  Kew  Zealand, 
are  contained  in  andesitic  rocks,  which,  near  the  fissures,  have 
suffered  considerable  alteration.  The  character  of  this  altera- 
tion has  been  described  by  F.  W.  Hutton*  in  a  report  on  the 
rocks  of  the  Hauraki  gold-fields,  which  include,  among  others, 
the  Thames  district,  and  are  situated  near  Auckland  on  the  north- 
ern island.  Triassic  or  pre-Triassic  sediments  are  unconform- 
ably  overlain  by  younger  volcanic  formations  which  contain 
the  gold-deposits.  The  rocks  consist  largely  of  andesite,  both 
augitic  and  hornblendic,  which  is  accompanied  by  masses  of 
tuffs  and  breccias.  Rhyolite  and  dacite  also  occur.  The  altera- 
tion, chiefly  of  propylitic  character,  is  distinguished  by  the  ap- 
pearance of  much  secondary  chlorite,  not  only  in  the  bisilicates 
but  also  in  the  ground-mass  and  in  the  feldspars,  the  latter,  be- 
sides, altering  to  calcite  and  "kaolin."  The  chlorite  alters 
again,  in  places,  to  a  mineral  which,  from  the  description  of  the 
author,  probably  is  sericite.  Another  common  secondary  prod- 
uct is  quartz  in  fine  aggregates.  The  pyrite  frequently,  though 
not  always,  present,  is  sometimes  derived  from  magnetite.  In 
other  cases  it  is  associated  with  the  product  of  decomposition 
of  titanic  iron-ore,  usually  referred  to  as  leucoxene.  The  color 
of  the  rocks  subjected  to  the  propylitic  alteration  is  greenish 
grey,  which,  on  further  alteration,  changes  into  lighter  tints. 
The  process  is  illustrated  by  several  analyses  by  Skey,  but  they 
only  throw  an  imperfect  light  upon  the  subject,  as  the  alkalies 
are  not  separated,  nor  C02  and  H20  individually  determined. 

Prof.  Hutton  is  a  pronounced  advocate  of  lateral  secretion, 
and  believes  that  the  gold  was  derived  from  the  surrounding 
volcanic  rock.  This  conclusion  is  disputed  by  Dr.  Don.f 

*  Austral  Ass.  Adv.  ScL,  vol.  i.,  1887,  pp.  245-274. 

f  "The  Genesis  of  Certain  Auriferous  Lodes,"  Trans.,  xxvii.,  586. 


572  METASOMATIC    PEOCESSES   IN   FISSURE-VEINS. 

Alaska. — The  Apollo  mine  on  Unga  Island,  described  by 
Gr.  F.  Becker,*  is  an  interesting  deposit  in  andesitic  rocks.  The 
ores  consist  of  pyrite,  galena,  zinc-blende,  chalcopyrite,  with  a 
little  calcite.  Native  gold  and  copper  occur  with  these  ores, 
and  the  presence  of  a  small  quantity  of  orthoclase  has  also  been 
proved.  According  to  Becker,  the  ore  is  present  exclusively 
as  the  filling  of  cavities,  and  shows  beautiful  comb-structure. 
In  the  vicinity  of  this  deposit,  the  andesites  are  highly  chloritic 
and  contain  abundant  pyrite.  Neither  sericite  nor  carbonates 
are  mentioned.  The  course  of  the  alteration  is  very  clearly 
propylitic.  The  pyrite  in  the  altered  rock  is  largely  derived 
from  the  ferro-magnesian  silicates. 

Silver  Cliff,  Colorado. — The  deposits  of  Silver  Cliff  should 
probably  be  referred  to  the  propylitic  class,  although  sericiti- 
zation  here  also  appears  as  a  very  important  metasomatic  char- 
acteristic. The  districts  of  Silver  Cliff  and  the  Rosita  Hills,  as 
described  by  Messrs.  Emmons  and  Cross,f  are  characterized 
by  a  complex  of  andesites,  rhyolites  and  trachytes,  resting  on 
old  Archean  rocks  and  erupted  through  them.  The  igneous 
rocks  and,  to  some  extent,  the  old  gneisses  are  traversed  by  a 
system  of  veins  and  irregular  deposits  carrying  chiefly  silver- 
ores,  consisting  of  tetrahedrite,  stephanite,  pyrite,  chalcopyrite 
and  galena,  in  a  gangue  of  barite  with  a  little  calcite.  The 
ore  consists  chiefly  of  altered  country-rock  in  which  the  differ- 
ent sulphides  and  gangue-minerals  have  been  developed  by 
metasomatic  replacement.  Mr.  Emmons  considers  that  the 
solutions  first  filled  narrow  fissures  between  sheeted  rocks,  and 
from  these  fissures  gradually  worked  into  the  rock  itself.  The 
whole  occurrence  at  Silver  Cliff  appears  to  show  strong  anal- 
ogy with  that  of  Cripple  Creek  and  Nagyag ;  for  in  all  of 
these  places  a  relatively  small  complex  of  Tertiary  eruptive 
rocks,  at  or  near  the  point  of  eruption,  has  been  traversed  by  a 
complicated  system  of  fractures  along  which  the  ore  has  been 
deposited  by  solutions  penetrating  the  fissures,  as  a  later 
manifestation  of  the  eruptive  activity. 

Over  large  areas  the  rock,  especially  the  andesite,  is  much 
decomposed  and  bleached,  and  also  contains  a  considerable 

*  18th  Ann.  Rept.  U.  S.  Geol  Surv.,  part  iii.,  p.  83. 

f  Yltli  Ann.  Rept.  U.  S.  Geol.  Surv.,  part  ii.,  pp.  269-472. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  573 

amount  of  pyrite.  The  greenish  color  first  appearing  is  due 
to  the  development  of  chlorite,  the  pyroxene  being  replaced 
by  chlorite,  calcite  and  quartz.  Further  alteration  results  in 
a  strong  sericitization,  and  in  removal  of  iron  and  lime.  The 
biotite  always  changes  into  muscovite,  which  sometimes  con- 
tains crystals  of  anatase.  The  lime-soda  feldspars  are  also  re- 
placed by  aggregates  of  muscovites,  but  the  potash-feldspars 
are  rarely  altered  until  all  the  other  minerals  have  been  almost 
completely  decomposed.  The  magnetite  disappears  with  the 
silicates.  Pyrite  is  common,  and  in  certain  cases  seems  to  be 
a  direct  replacement  of  magnetite.  Calcite  is  frequently  asso- 
ciated with  muscovite,  and  may  replace  plagioclase  or  augite. 
Mr.  Cross  recognized  no  kaolin  in  noteworthy  amount  among 
the  products  of  alteration.  In  some  instances  the  bleaching 
extends  through  large  rock-masses,  but  it  clearly  proceeds 
from  fissures.  Near  the  veins,  the  bleached  rock  adjoining  the 
small  fissures  may  gradually  shade  off  into  fresh  rock  within  a 
few  feet. 

A  silicification  is  noted  in  some  cases,  especially  in  the  case 
of  a  dike  of  rhyolite,*  which  has  suffered  so  great  alteration  as 
to  be  almost  completely  changed  to  quartzose  fine-grained  ma- 
terial. The  andesite  may  also  occasionally  show  silicification. 
The  rhyolite  is  altered  in  some  places  to  soft,  whitish  material, 
and  in  other  places  to  hard  cavernous  quartzose  material. 
The  contacts  of  rhyolite  and  andesite  are  sometimes  changed 
to  such  a  degree  as  to  make  rock-determination  very  difficult. 

Silver  City,  Idaho. — The  fissure-vein  of  .the  Trade  Dollar  and 
Black  Jack  mines,  Florida  mountain,  near  Silver  City,  Idaho, 
presents  some  unusual  features,  f  The  sharply  defined  vein  cuts 
across  granite,  basalt  and  rhyolite.  The  ores  consist  of  argen- 
tite  and  chalcopyrite  in  a  gangue  of  quartz  and  valencianite 
(orthoclase),  forming  typical  fillings  of  open  spaces.  The  al- 
teration affects  the  various  rocks  somewhat  differently ;  but 
the  vein  is  undoubtedly  of  the  propylitic  class,  in  the  forma- 
tion of  which  alkaline  carbonates  and  carbon-dioxide  were 
present  only  in  small  amounts. 

In  the  granite  the  adjoining  rock  is  very  slightly  altered, 
though  spaces  of  dissolution  and  crushed  portions  in  it  may  be 
filled  with  quartz  and  valencianite. 

*  Loc.cit.,  p.  358. 

f  W.  Lindgren,  2,0th  Ann.  Eept.  U.  S.  Geol.  Surv.,  pt.  iii.,  pp.  134-144, 174-187. 


5V4  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

The  rhyolite  is  extensively  altered  and  somewhat  silicified, 
the  quartz  crystals  having  received  aureoles  of  the  same  min- 
eral in  secondary  deposition.  The  feldspars  are  often  con- 
verted into  fine-grained  quartz  and  sericite,  the  ground-mass 
being  changed  to  the  same  minerals,  and  the  quartz  predomi- 
nating. A  little  kaolinite  is  probably  also  present,  and  pyrite 
in  small  cubes  is  scattered  through  the  rock.  Near  the  under- 
lying basalt,  epidote  and  chlorite  have  been  introduced  into  the 
rhyolite,  indicating  an  upward  movement  of  the  solution. 

The  basalt  is  also  considerably  altered,  and  the  character  is 
typically  propylitic,  with  abundant  chlorite  and  pyrite,  and 
slight  changes  otherwise  in  the  chemical  constitution. 

6.  Fluoritic  Gold-Tellurium  Veins. 

This  peculiar  and  interesting  class  of  deposits,  the  discovery 
and  study  of  which  date  only  a  few  years  back,  is  character- 
ized by  the  appearance  of  tellurides  of  gold  and  silver,  besides 
a  little  native  gold ;  by  the  universal  presence  of  (usually  pur- 
ple) fluorite ;  and  by  an  intense  inetasomatic  action — so  that 
the  larger  proportion  of  the  ores  consists  of  altered  country- 
rock.  The  gangue  is  quartz,  fluorite  and  barite ;  ore-minerals, 
except  tellurides,  are  not  very  abundantly  present. 

The  age  of  these  deposits,  as  thus  far  known,  is  probably 
Tertiary,  following  the  outbreaks  of  phonolitic  magmas,  with 
which  all  of  the  occurrences  show  a  remarkable  connection. 
The  depositing  waters  must  have  been  poor  in  carbon-dioxide, 
alkaline  and  earthy  carbonates,  but  contained  more  or  less  fluor- 
ine as  hydrofluoric  acid,  which  is  possibly  indicated  by  the  abun- 
dant spaces  of  dissolution  in  the  granite  of  Cripple  Creek.  Or 
else  (and  this  was  probably  the  more  common  case)  they  con- 
tained alkaline  fluorides.  Though  the  veins  are  closely  con- 
nected with  the  eruption  of  phonolitic  magma  referred  to,  it  is 
not  believed  that  the  conditions  of  deposition  were  of  pneuma- 
tolytic  character,  but  rather  that  they  were  normally  hydro- 
thermal. 

Cripple  Creek. — The  geology  and  mineral  deposits  of  the  Crip- 
ple Creek  district,  Colo.,  have  been  examined  by  Whitman 
Cross  and  E,.  A.  F.  Penrose.*  The  general  occurrence  of  the 
veins  is  somewhat  analogous  to  that  of  Nagyag,  Hungary,  and 

*  16th  Annual  Report  U.  S.  Geol.  Surv.,  part  ii. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  575 

Silver  Cliff,  Colorado,  inasmuch  as  they  cut  igneous  masses, 
here  consisting  of  andesite  and  phonolite,  and  occur  in  close 
proximity  to  the  original  locus  of  eruption  of  these  rocks.  The 
veins,  of  which  there  are  a  great  number,  contain  native  gold, 
tellurides  and  pyrite,  together  with  a  little  galena  and  zinc- 
blende.  Silver  is  present  in  very  small  amounts  only.  The 
gangue  consists  of  quartz,  fluorite  and  barite.  Prof.  Penrose 
designates  the  veins  as  very  largely  replacement  veins,  formed 
by  metasomatic  action  of  the  solutions  ascending  in  narrow 
fissures  on  the  surrounding  country-rock.  Filling  of  open  fis- 
sures exists  to  a  subordinate  extent.  Large  masses  of  the  vol- 
canic rocks,  especially  the  porous  tuffs,  were  subjected  to  ther- 
mal action  prior  to  the  formation  of  some  of  the  fissures.  The 
alteration  results  in  silicification,  kaolinization  and  some  seri- 
citization.  In  the  breccia  and  tuff,  the  process  consists  in  the 
total  destruction  of  the  dark  silicates,  and  the  substitution  of  a 
white  mica  for  them.  The  feldspar  changes  to  muscovite  or 
kaolin ;  the  only  fresh  remaining  crystals  consist  of  apatite ; 
and  the  rocks  are  greatly  impregnated  with  pyrite.  In  some 
places  the  alteration  consists  in  a  silicification,  but  more  com- 
monly muscovite  or  kaolin  are  the  minerals  formed.  Penrose 
says  also  that  kaolin  occurs  in  the  veins  in  irregular  masses, 
mixed  with  quartz.  Three  analyses  of  this  product  show  that 
it  is  a  normal  kaolin.  While  it  is  conceded  that  the  kaolin  is 
to  some  extent  the  result  of  surface  alteration,  its  formation 
was  chiefly  earlier  than  the  development  of  this  superficial 
alteration.  The  quantity  of  kaolin,  he  says,  does  not  diminish 
in  depth,  where  it  still  occurs  associated  with  unaltered  sulphides. 

An  opaline  silica  is  also  found  in  the  veins,  often  appearing 
like  red,  brilliant,  conchoidal  jasper.  An  analysis  of  it  shows: 
Si02,  72.46;  A1203,  2.52;  Fe203,  17.88;  CaO,  0.14;  MgO,  trace; 
K20,  1.08;  E"a20,  0.06;  H20,  5.70;  total,  99.84  per  cent. 

The  origin  of  this  product  is  not  stated,  but  it  is  not  improb- 
ably the  result  of  extreme  alteration  of  a  volcanic  rock.  It  is 
interesting  to  note  that  among  the  alkalies  K20  strongly  pre- 
dominates, and,  to  judge  from  the  analysis,  the  rock  must  con- 
tain about  10  per  cent,  of  sericite. 

During  the  last  year  I  had  opportunity  to  examine  a  suite  of 
specimens  collected  by  Mr.  S.  F.  Emmons  from  the  Independ- 
ence and  Portland  mines;  and  some  of  the  results  are  here 


576  METASOMATIC    PROCESSES    IN   FISSURE-VEINS. 

published  with  his  permission.  At  these  mines,  the  narrow 
fissure  along  which  the  replacement  took  place  cuts  both  the 
granite  and  the  andesite-granite  breccia,  and  in  places  follows 
a  dike  of  phonolite.  The  specimens  clearly  bear  out  previous 
statements  as  to  replacement.  In  addition  to  the  fluorite,  sec- 
ondary orthoclase,  or  valencianite,  was  recognized  as  a  univer- 
sally present  gangue-mineral.  The  granite-ore  from  both  mines 
consists  of  a  coarsely  granular  rock,  largely  of  microcline  and 
quartz,  made  cellular  and  porous  by  spaces  of  dissolution.  The 
cavities  are  coated  with  abundant  small  and  clear  crystals  of 
valencianite  showing  the  usual  combination  of  prism  and  dome ; 
also  with  a  little  pyrite,  gold,  and  small  cubes  of  fluorite.*  The 
crystals  of  valencianite  were  isolated  and  conclusively  iden- 
tified by  qualitative  analysis  and  tests.  Microscopic  analysis 
reveals  but  little  alteration  in  the  granite,  though  the  biotite 
foils  are  replaced  by  a  substance  which  appears  to  be  valen- 
cianite. The  feldspars  contain  a  few  shreds  of  sericite,  and 
pentagonal  crystals  of  pyrite  are  scattered  through  feldspar  and 
altered  biotite.  In  places,  small  replacement- veinlets  of  fluorite 
and  quartz  traverse  the  feldspar.  The  cavities  of  dissolution 
apparently  result  from  the  removal  of  both  quartz  and  micro- 
cline. Some  of  them  are  filled  with  quartz,  valencianite  and 
pyrite ;  the  secondary  feldspar  often  being  deposited  with  orien- 
tation parallel  to  that  of  older  grains.  A  few  grains  of  sec- 
ondary feldspar  show  microcline  structure,  but  most  of  them 
are  simple  individuals.  These  filled  spaces,  characterized  by 
crustification,  are  illustrated  in  Fig.  11. 

The  processes  of  replacement  are  remarkably  variable.  In 
some  of  the  granite-andesite  breccias  the  result  is  quartz,  valen- 
cianite, fluorite  and  pyrite.  Fig.  10  shows  how  the  replace- 
ment progresses  in  a  grain  of  orthoclase.  Fig.  8  shows  a  filled 
veinlet  in  the  same  breccia,  which  by  means  of  a  narrow  crack 
connects  with  the  feldspar  grains  just  mentioned.  The  valen- 
cianite shows  crustification,  while  the  fluorite  and  pyrite,  by  cor- 
roding the  walls,  indicate  partial  metasomatic  action. 

Some  of  the  phonolites  of  the  Independence  mine  are  porous 
siliceous  rocks,  completely  replaced  with  quartz,  valencianite 
crystals,  pyrite,  and  a  few  grains  of  a  telluride  of  gold  and 

*  Confer:  W.  Lindgren,  "The  Gold  and  Silver  Veins  of  Silver  City,"  2Qth 
Ann.  Rept.  U.  S.  Geol.  Surv.,  part  iii.,  p.  167. 


METASOMATIC    PROCESSES   IN   FISSURE-VEINS.  577 

silver.  Other  specimens  show  only  incipient  alteration,  being 
impregnated  with  pyrite  crystals  and  containing  a  few  per  cent, 
of  sericite ;  they  contain,  besides,  spaces  of  dissolution  filled 
with  quartz,  fluorite  and  valencianite.  Certain  fine-grained 
granitic  breccias  from  the  Annie  Lee  shoot,  in  the  Portland 
mine,  show  a  most  peculiar  alteration,  the  quartz  and  ortho- 
clase  being  both  replaced  by  calcite,  pyrite  and  secondary  or- 
thoclase.  The  final  result  of  the  alteration  of  phonolite  is,  in 
many  cases,  a  purple  fine-grained  rock  consisting  of  quartz, 
fluorite  and  pyrite;  as  usual,  the  fluorite  is  crystallized;  and 
the  quartz  also  shows,  to  some  extent,  idiomorphic  outlines 
(Fig.  9). 

Other  Occurrences. — To  this  class  belong  also  the  so-called 
Potsdam  tellurium-ores  ot  the  Black  Hills,  Dakota,  de- 
scribed by  Devereux,  Carpenter,  F.  Clemes  Smith,  and  lately 
by  J.  D.  Irving.*  According  to  Mr.  Irving,  the  irregular  de- 
posits are  connected  with  fissures,  and  consist  in  a  replacement 
of  limestone  by  silica,  with  fluorite,  and  gold,  partly  in  the 
form  of  tellurides.  While  the  age  of  these  deposits  is  not 
fully  known,  they  are  believed  to  be  genetically  connected 
with  phonolitic  and  tinguaitic  dikes  of  Tertiary  age. 

Mr.  W.  H.  Weedf  has  described  interesting  occurrences  of 
the  same  type  from  the  Judith  mountains  in  northern  Mon- 
tana. The  deposits,  though,  strictly  speaking,  not  fissure- veins, 
are  still  more  or  less  clearly  connected  with  fractures,  and  are 
found  in  the  brecciated  contact-zone  between  limestone  and  in- 
trusive masses  of  acidic  porphyry.  The  principal  gangue-min- 
erals  are  quartz  and  purple  fluorite,  the  ore-minerals  being  na- 
tive gold  and  tellurides  of  gold  and  silver.  The  mode  of  ore- 
deposition  is  certainly  a  replacement  of  limestone,  the  fluorite 
occurring  in  more  or  less  sharply  defined  patches  in  the  lime- 
stone breccia.  From  a  specimen  which  Mr.  "Weed  kindly 
selected  for  me  a  section  was  cut,  which  is  partly  illustrated  in 
Fig.  14.  The  invasion  of  the  normal  limestone,  still  carrying 
organic  remains,  by  the  crystallizing  fluorite,  is  well  shown,  as 
well  as  the  incipient  silicification  which  accompanied  the  meta- 
somatic  action.  Much  secondary  silica,  replacing  limestone, 

*  "  A  Contribution  to  the  Geology  of  the  Northern  Black  Hills,"  Ann.  N.  T. 
Acad.  Sci.,  vol.  xii.,  No.  9,  pp.  297-314. 

t  18th  Ann.  Rept.  U.  S.  Geol.  Surv.,  part  iii.,  p.  588. 


578  METASOMATIC    PROCESSES    IN   FISSURE-VEINS. 

also  occurs  in  jaspery  or  cherty  form.  Small  cubes  of  fluorite, 
found  in  the  fresh  limestone,  represent  places  of  incipient  fluor- 
itization.  Dikes  and  sheets  of  phonolitic  rocks  are  found  in 
the  vicinity  of  the  deposits.  A  deposit  occurring  in  rhyolite 
porphyry  not  far  from  the  limestone  shows  strong  alteration  of 
the  country-rock.  The  feldspar  is  here  changed  to  sericite, 
the  ferro-magnesian  minerals  are  transformed  to  calcite,  and 
abundant  small  crystals  of  pyrite  appear  in  the  rock.  Fluorite 
is  also  present  on  some  of  the  veins  in  rhyolite  porphyries. 
Mr.  Weed  regards  the  deposits  as  possibly  of  pneumatolytic 
origin.  It  is  scarcely  necessary,  however,  to  assume  the  fluor- 
ine to  have  been  present  in  the  form  of  free  hydrofluoric  acid 
(compare  pp.  521  and  524). 

Similar  deposits,  with  purple  fluorite  and  tellurides,  are 
also  described  by  Mr.  Weed  from  the  Little  Rocky  Mountains, 
in  Montana.* 

7.  Sericitic  and  Kaolinitic  Gold-  and  Silver-  Veins. 

General  Remarks. — This  class  has  not  been  studied  as  much 
as  some  of  the  other  subdivisions,  but  many  deposits  will  prob- 
ably be  found  to  belong  to  it.  Apparently  the  pure  aluminic 
silicate  cannot  be  formed  when  the  generating  waters  contain 
much  carbon  dioxide  or  alkaline  carbonates.  But  it  does  form 
under  the  influence  of  some  waters  containing  a  small  amount 
of  these  reagents,  and  also  in  the  presence  of  sulphuric  acid, 
which,  as  is  well  known,  rapidly  attacks  the  feldspars.  Even 
under  the  latter  two  conditions,  some  sericite  is  ordinarily  also 
formed ;  and  I  am  not  aware  of  any  veins  in  which  kaolinite 
forms  without  sericite.  The  class  may  be  subdivided  accord- 
ing to  the  absence  or  presence  of  silicification. 

The  Freiberg  Veins. — As  is  well  known,  several  very  different 
kinds  of  veins  appear  in  the  Freiberg  district,  practically  all, 
however,  being  sharply  defined  fissure- veins  in  gneiss,  in  which 
the  filling  of  open  spaces  constitutes  the  only  ore ;  extensive 
zones  of  alteration  are  absent.  It  is  a  peculiar  fact  that  very 
little  is  known  of  the  metasomatic  processes  affecting  the  coun- 
try-rock at  this  celebrated  locality,  no  chemical  examinations 
having  been  made  to  determine  how  the  various  classes  of 

*  Journal  of  Geol,  vol.  iv.,  pp.  399-428  (1896). 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  579 

veins  may  differ  in  their  metasomatic  products.  A  letter  from 
Prof.  Beck,  of  Freiberg,  informs  me  that  Prof.  A.  W.  Stelzner 
devoted  much  time  during  the  last  years  of  his  life  to  the  exami- 
nation of  the  changes  in  the  country-rock  adjoining  the  veins, 
hut  that  his  manuscript  notes  have  never  been  published. 

W.  Yogelgesang,*  in  describing  the  veins  south  and  southeast 
of  Freiberg  containing  carbonates  and  rich  silver-ores,  describes 
the  impregnation  of  the  adjoining  rock  with  ores.  He  men- 
tions the  occasional  introduction  of  argentite  and  native  silver 
into  the  gneiss,  also,  in  places,  of  arsenopyrite,  pyrite,  chalco- 
pyrite,  zinc-blende  and  galena.  The  impregnation  with  silver- 
ores  appears  only  in  especially  rich  places  along  the  vein.  In 
one  case,  however,  the  impregnated  rock  appears  as  an  irregu- 
lar, limited  mass,  almost  entirely  independent  of  the  direction 
of  the  vein.  In  another  locality,  chalcopyrite  and  bornite  were 
found  in  the  wall-rock,  while  the  filling  of  the  vein  contained 
neither.  In  the  same  paper,  the  author  describes  the  alteration 
of  the  so-called  normal  gneiss  of  Freiberg  near  the  veins  of  the 
Kiesige  jBleiformation.  The  mica  is  the  first  mineral  attacked ; 
the  second  is  the  feldspar.  The  former  acquires  a  silvery- 
white  color,  often  connected  with  a  chloritic  appearance.  The 
feldspar  is  changed  to  a  white  "  kaolin,"  and  the  whole  rock  is 
bleached  white.  By  extreme  alteration,  the  quartz  disappears, 
and  the  rock  forms  a  white  or  yellowish-white  talc-like  mass. 
The  altered  rock  is  frequently,  in  fact  usually,  filled  with 
arsenopyrite.  Some  of  the  crystals  are  large;  others  micro- 
scopic ;  and  their  amount  may  so  increase  as  to  form  a  con- 
nected, compact  mass  of  arsenopyrite.  All  these  crystals  are 
twins,  excellently  developed,  with  perfect  faces.  This  descrip- 
tion refers  especially  to  the  Dietrich  Stehender  vein.f  In  the 
foot-wall,  and  partly  also  in  the -hanging-wall,  of  this  altered 
mass  appears  a  rock,  recognizable  as  the  ordinary  grey  gneiss 
of  Freiberg.  It  contains  no  aresenopyrite  but  is  strongly  im- 
pregnated with  galena,  arranged  in  curved  streaks  parallel  to 
the  schistosity,  and  replacing  one  constituent  of  the  rock, 
namely,  the  feldspar.  The  altered  rocks  have  been  analyzed; 
but  the  determination  of  alkalies  being  omitted,  the  analyses 
have  no  special  value. 

*  Bernard  Cotta,  Gangstudien,  vol.  ii.,  Freiberg,  1854,  p.  78. 
t  The  sericite  from  this  vein  has  been  analyzed  by  H.  Schulze  ;  see  page  609. 

37 


580  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

The  rock  adjoining  the  Gotthold-Stehender  vein  is  likewise 
strongly  impregnated ;  but  here,  besides  arsenopyrite,  galena, 
chalcopyrite,  pyrite  and  zinc-blende  are  also  found. 

As  early  as  1883  and  1884  Stelzner*  devoted  considerable  at- 
tention to  the  examination  of  the  soft  and  altered  rock  adjoin- 
ing the  veins  of  Freiberg.  These  altered  rocks  are  also  usu- 
ally impregnated  with  small  crystals  of  arsenopyrite,  or  pyrite, 
or  (more  rarely)  zinc-blende  and  galena.  In  the  normal  gneiss 
of  Freiberg,  which  Prof.  Stelzner  subjected  to  separation  by 
heavy  solutions,  he  found  much  zircon,  as  well  as  a  little  tour- 
maline and  a  large  quantity  of  apatite.  All  three  of  these  min- 
erals were  also  separated  from  the  altered  wall-rocks  in  the 
crystalline  shape  which  they  had  had  in  the  fresh  rock  ;  hence 
none  of  them  had  been  attacked.  He  observes  further  that  the 
quartz,  feldspar  and  biotite  of  the  fresh  gneiss  is  completely  or 
almost  completely  changed  into  white  potassium  mica,  form- 
ing, in  small  hexagonal  or  irregular  foils,  the  chief  mass  of  the 
rock.  This  secondary  mica  contains,  according  to  analysis  by 
Dr.  Schulze,  as  much  as  0.41  per  cent,  of  Ti02  and  0.54  per 
cent,  of  Sn02.  As  newly-formed  minerals  in  the  altered  rock, 
appear  small  crystals  of  quartz,  rutile  and  anatase.  In  certain 
of  the  examined  rocks  only  rutile  was  found,  in  others  only  ana- 
tase (octahedrite),  but  both  were  present  as  sharply  defined  small 
crystals.  These  two  minerals  are  considered  as  resulting  from 
a  decomposition  of  the  biotite,  which  is  rich  in  titanic  acid.  In 
analyzing  the  heaviest  part  obtained  by  the  Thoulet  solution 
from  the  altered  rock  close  to  one  of  the  veins,  it  was  found 
that  cassiterite  was  present  in  notable  quantity.  Whether  this 
tin-ore  resulted  from  the  decomposition  of  the  biotite,  or 
whether,  like  the  arsenopyrite,  it  had  been  introduced  from  the 
vein-fissure,  is  not  certain.  The  latter  hypothesis  is  probable; 
for  the  black  zinc-blende  of  the  same  vein  (the  Carl  Stehender) 
contains  small,  but  numerous,  crystals  of  cassiterite. 

Examination  of  the  fresh  gneisses  of  Freiberg  discloses  the 
presence  of  pyrrhotite,  pyrite,  and  probably  also  a  little  arseno- 
pyrite. These  are  presumably  primary ;  at  least  the  statement 
of  Prof.  Stelzner  is  probably  to  be  interpreted  in  this  sense. 

The  first  attempt  to  examine  the  altered  wall-rocks  in  a  sci- 

*  A.  W.  Stelzner,  u  Studies  of  the  Gneiss  of  Freiberg  and  its  Products  of  Alter- 
ation." Neues  Jahrbuch,  1884,  vol.  i.,  p.  271. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  581 

entific  manner  was  made  by  Prof.  Th.  Scheerer,*  in  connec- 
tion with  his  classic  paper  on  the  gneissic  rocks  from  the 
vicinity  of  Freiberg.  According  to  Scheerer,  the  normal  char- 
acter of  the  grey  gneiss  is  always  more  or  less  changed  in  the 
vicinity  of  mineral  veins,  the  extension  of  this  alteration  being, 
in  general,  dependent  upon  the  width  of  the  vein.  The  mica 
has  turned  into  a  light  greenish-grey  or  white  talcose  mass ;  and 
the  whole  rock  is  softened  and  easily  crushed.  The  width  of 
this  alteration  ranges  from  a  few  inches  up  to  6  feet.  In  the 
porous  gneiss,  small  bodies  of  pyrite,  zinc-blende  and  galena 
have  been  formed ;  partly  as  separate  crystals,  and  partly  in 
little  veinlets.  Prof.  Scheerer  examined  especially  a  gneiss 
closely  adjoining  the  Erzengel  vein  belonging  to  the  Kiesige 
Blei formation,  in  the  Himmelfahrt  mine.  The  specimen  was 
taken  from  one  of  the  deep  levels,  thus  eliminating  the  action 
of  surface-water.  The  analysis  gave:  Si02,  61.69;  Ti02,  0.73; 
A1203,  21.74;  Fe203,0.43;  CaO,  1.07  ;  MgO,  1.15  ;  K20,  2.69; 
Na20,  0.30  ;  H20,  3.96  ;  fluorite,  1.20  ;  pyrite,  4.26  ;  chalcopyr- 
ite,  0.23  ;  galena,  0.09;  argentite,  trace;  total,  99.54  per  cent. 

Scheerer  recalculated  this  analysis  on  the  basis  of  constant 
alumina  and,  combining  the  result  with  the  analyses  of  the  fresh 
rock,  obtained  the  table  on  the  following  page.  The  assumed 
constancy  of  the  alumina  is  probably  not  quite  correct,  but  offers 
an  easy  and  fairly  accurate  way  of  approximately  judging  the 
changes  that  have  taken  place. 

This  result  is  remarkable  in  many  respects.  First,  we  note 
that  a  very  decided  removal  of  substance  has  taken  place. 
Counting  by  equal  weights,  only  5  parts  in  100  have  been 
added  (even  less,  if  we  consider  that  the  Fe  of  FeS  is  derived 
from  Fe203  and  FeO  in  the  fresh  rock)  while  no  less  than  42.45 
parts  have  been  carried  away.  This  contrasts  strongly  with 
the  results  obtained  from  gold-quartz  veins  in  California  and 
Idaho.  Of  the  silica,  26.62  parts  or  40  per  cent,  is  removed. 
The  total  bases,  except  alumina,  have  been  diminished  to  the 
extent  of  81.01  per  cent.  Both  K20  and  N"a20  have  been 
removed ;  the  former,  however,  in  much  smaller  proportion 
than  the  latter.  Lime,  magnesia  and  iron  have  also  been  very 
greatly  reduced.  A  large  part  of  the  iron,  however,  appears  to 

*  Zeitschr.  d.  d.  geol  Qes.t  vol.  xiv.,  p.  87  (1862). 


582 


METASOMATIC    PROCESSES   IN   FISSURE-VEINS. 


Normal  Grey  Gneiss. 

Altered  Grey  Gneiss. 

Additions  and  Sub- 
tractions Suffered  by 
the  Altered  Rock. 

SiO2.... 

Per  cei 
65.42 
1.05 
13.68 
4.26  "I 
2.88 
1.44 
2.66 
6.18 
1.38 
1.05 

trace 
trace 
trace 

it. 
18.80 

Per  cent. 
38.80 
0.46 
13.68 
0.27  1 
i         .   ,. 

0.67   1  „  -A 
0.73  f3-56 
1.70 
0.19  J 
2.49 
0.76 
2.68 
0.15 
0.06 
trace 

Per  cei 
-26.62 
-0.59 

-3.99 
-2.88 
-0.77 
-1.93 
-4.48 
-1.19 
+1.44 
+0.76 
+2.68 
+0.15 
+0.06 
trace 

it. 
-15.24 

TiO2 

ALO, 

Fea 

FeO 

CaO.    . 

MffO 

K2O. 

Na2O 

H2O. 

Fluorite 

Pyrite  

Chalcopyrite   

Galena  

Argentite  

100.00 

62.64 

-42.45 
+5.09 
37.36 

100.00 

have  been  transformed  into  pyrite.  There  are  no  carbonates 
at  all,  while  a  little  fluorite  has  formed. 

Of  course,  no  microscopic  diagnosis  of  Scheerer's  specimens 
is  now  available.  But  from  Stelzner's  later  separations  and 
Schulze's  analysis  it  is  clear  that  considerable  sericite  is  pres- 
ent. An  attempt  to  calculate  Scheerer's  analysis  shows  at  once 
that  kaolinite  is  also  present.  A  rough  calculation  gives  the  fol- 
lowing result:  Quartz,  40;  sericite,  32;  chlorite,  3.20;  kaolin- 
ite, 17.70;  titanite,  1.90;  fluorite,  1.20;  pyrite,  4.26;  chalco- 
pyrite,  0.23;  galena,  0.09;  total,  100.58  per  cent. 

In  this  calculation  K20  +  JsTa20  are  taken  as  a  basis  for  sericite, 
according  to  Schulze's  analysis ;  MgO  is  calculated  as  chlorite ; 
the  remaining  H20  is  calculated,  with  proper  quantities  of 
A1203  and  Si02,  as  kaolinite;  and  there  is  a  small  excess  of 
CaO,  possibly  belonging  to  apatite.  ¥205  ^  n°t  determined 
in  the  analysis.  But  there  remains  also  an  excess  of  4  per  cent, 
of  A1203,  which  is  inexplicable  on  the  basis  of  this  assumed 
mineral  composition ;  and  it  is  difficult  to  see  how  this  should 
be  treated.  Possibly  the  determination  of  H20  is  a  little  too 
low.  At  any  rate,  a  considerable  amount  of  kaolinite  is  surely 
present.  This  result  is  of  great  interest.  The  strong  leaching 
of  Si02  and  bases,  as  well  as  the  presence  of  kaolinite  together 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  583 

with  sericite,  points  to  a  process  and  to  water  very  different 
from  those  by  which  sericite  alone  is  produced.  It  is  not  out 
of  place  in  this  connection  to  call  attention  to  the  presence  of 
fluorite  and  to  the  close  relationship  which,  as  indicated  by 
Dalmer,  exists  between  the  cassiterite-veins  and  those  of  the 
Kiesige  Bleiformation  of  the  Erzgebirge,  a  relationship  still  further 
emphasized  by  the  occurrence  of  cassiterite  in  the  Freiberg 
veins.  Scheerer  believed  that  the  grey  gneiss,  by  reason  of  its 
easily-attacked  biotite,  had  a  precipitating  influence  on  the 
mineral  waters.  The  red  gneiss,  containing  muscovite  in  gen- 
eral, carries  no  large  bodies  of  ore. 

De  Lamar,  Idaho. — The  quartz  veins  of  De  Lamar,  Idaho, 
belong  to  that  class  in  which  the  alteration  of  the  country-rock 
results  in  sericite,  kaolinite  and  quartz.*  These  ores,  which 
carry  finely-divided  gold,  together  with  some  rich  silver  min- 
erals, are  peculiar,  because  the  quartz  now  constituting  the  fill- 
ing is  pseudomorphic  after  a  former  vein-filling  of  calcite.  The 
country-rock  has  undergone  two  corresponding  changes  :  the 
first  consisting  in  a  normal  sericitization ;  the  second  in  a  silici- 
fication,  probably  under  the  influence  of  waters  containing 
sulphuric  acid.  The  final  result  is  that  the  rhyolite  is  converted 
to  a  silicified  rock,  in  which  the  structure  is  plainly  preserved. 
The  phenocrysts  of  quartz  have  received  aureoles  of  secondary 
silica ;  and  the  feldspars  are  fully  converted  into  fine-grained 
aggregates  of  quartz.  The  composition  is  as  follows  :  Sericite, 
15.43;  kaolinite,  3.81;  quartz,  78.73;  pyrite,  0.90,  and  water 
(hygroscopic),  0.51;  total,  99.38  per  cent. 

Expressed  quantitatively,  the  process  appears  to  consist  in 
the  loss  of  nearly  all  of  the  soda,  half  of  the  alumina  and 
much  of  the  ferrous  and  ferric  oxide;  and  finally,  in  the  addition 
of  several  per  cent,  of  silica.  The  pseudomorphic  filling  con- 
sists of  crossing  laminae  of  quartz,  each  consisting  of  a  thin  plate 
of  microcrystalline  silica,  coated  on  both  sides  with  small  quartz 
crystals. 

The  character  of  the  process  involved  in  this  change  from 
calcite  to  quartz  is  probably  as  follows :  Calcite-filling  in  veins 
is  often  characterized  by  a  prevalence  of  long,  slender  or  spear- 
shaped  grains.  The  solutions  carrying  silica  penetrate  along 

*  W.  Lindgren,  20th  Ann.  Rept.  U.  S.  Geol  Surv.,  part  iii.,  p.  178  et  seq. 


584  METASOMATIC    PROCESSES    IN   FISSURE-VEINS. 

the  contact-planes  of  these  grains  and  deposit  their  plates  of 
microcrystalline  quartz  in  the  place  of  dissolved  calcite ;  from 
these  medial  plates  small  quartz  crystals  grow  into  and  gradu- 
ally replace  the  calcite  on  both  sides.  The  pseudomorphic 
plates  do  not,  as  a  rule,  follow  the  cleavage-planes ;  hence  there 
may  be  in  some  cases  considerable  difficulty  in  determining  the 
original  mineral  replaced  by  the  quartz.  The  subject  is  more 
fully  treated  in  my  report,  cited  above. 

Summit  District,  Colorado. — Some  remarkable  ore-deposits 
in  the  Summit  district,  Rio  Grande  county,  Colo.,  have  been 
described  by  R.  C.  Hills*  as  masses  of  quartz  resulting  from 
the  alteration  and  silicification  of  eruptive  rocks  along  contact- 
planes,  especially  between  rhyolite  and  trachyte-breccia.  The 
quartz,  which  contains  gold,  enargite,  pyrite,  galena  and  zinc- 
blende,  gradually  merges  into  rhyolite,  varying  in  thickness 
from  3  to  30  feet.  Thus  silicification  of  the  rhyolite  is  evident, 
and  has  resulted  in  a  change  of  the  ground-mass  to  compact 
quartz,  while  the  phenocrysts  of  that  mineral  remain  intact 
and  conspicuous.  The  sanidine  has  been  removed,  and  pseu- 
domorphic quartz  has  been  deposited.  The  surrounding  rock 
is  notably  kaolinized,  and  contains  no  lime  or  potash.  The 
alteration  probably  took  place  less  than  300  ft.  below  the 
original  surface. 

The  following  is  suggested  in  explanation  of  the  chemical 
processes :  Silica  is  practically  insoluble  in  solutions  contain- 
ing sulphates  and  chlorides,  hydrogen  sulphide  and  free  sul- 
phuric acid.  Under  these  conditions,  aluminum  silicates  are 
dissolved  and  sulphates  or  chlorides  of  aluminum  are  formed, 
with  simultaneous  separation  of  silica;  and  to  sulphuric  acid 
as  a  reagent  the  writer  believes  the  alteration  to  be  chiefly  due. 
Whether  the  metallic  minerals  were  deposited  simultaneously 
with  this  alteration,  or  subsequently,  is  left  an  open  question, 
though  it  is  believed  that  their  simultaneous  deposition  would 
be  possible. 

8.  Sericitic  and  Calcitic  Gold-Silver  Veins. 

This  important  metasomatic  class  comprises  an  enormous 
number  of  veins,  differing  widely  in  age  and  in  the  character 

*  Proc.  Colorado  Sci.  £bc.,  vol.  i.,  p.  20. 


METASOMATIC    PROCESSES   IN   FISSURE-VEINS.  585 

of  the  country-rock,  but  usually  characterized  by  quartz-filling, 
enclosing  auriferous  and  argentiferous  sulphides  (often  also  free 
gold),  while  the  adjoining  rock  for  a  short  distance  on  both 
sides  is  converted  into  an  aggregate  of  quartz,  sericite  and 
calcite,  with  some  metasomatic  sulphides.  Extensive  altera- 
tion-zones are  not  common;  and  sometimes  fresh  rock  may 
adjoin  the  vein.  The  relative  quantity  of  sericite  and  carbon- 
ates may  differ  considerably,  even  in  the  same  mine. 

The  Gold-Quartz  Veins  of  California. — These,  perhaps  the 
most  prominent  representatives  of  the  class,  have  been  studied 
in  some  detail.*  The  gold-quartz  veins  of  California  are 
fissure-veins  of  Cretaceous  age,  largely  filled  with  quartz  along 
open  spaces.  A  small  amount  of  calcite  may  also  occur.  The 
ore-minerals  comprise  native  gold,  present  in  a  free  state  at 
all  depths  reached  hitherto,  and  a  small  amount  of  sulphides 
consisting  of  pyrite  (never  marcasite  and  rarely  pyrrhotite), 
galena,  zinc-blende,  arsenopyrite  and  chalcopyrite.  Tellurides 
are  often  found,  but  in  small  quantity  only.  The  veins  are 
practically  independent  of  the  character  of  the  country-rock, 
cutting  almost  all  the  sedimentary  and  igneous  rocks  of  the 
Sierra  Nevada.  Adjoining  the  veins  the  country-rock,  for  a 
variable  distance,  but  seldom  exceeding  a  few  feet,  is  nearly 
always  altered  by  metasomatic  processes.  Clay-slates  and  sili- 
ceous schists  have  been  apparently  least  affected  in  this  way, 
except  that  they  are  generally  impregnated  with  pyrite.  More 
detailed  chemical  examinations  will  probably  show  that  even 
these  rocks  have  been  altered  more  than  their  appearance 
would  suggest. 

In  the  ordinary  course  of  the  metasomatic  process,  augite, 
hornblende,  epidote,  biotite  and  feldspars  are  first  vigorously 
attacked.  The  ferromagnesian  silicates  are  often  converted 
into  large  foils  of  muscovite.  The  alteration  proceeds  along 
cracks  and  cleavage-planes,  and  a  finely  felted  aggregate  of 
sericite  and  calcite  invades  the  grains  until  the  replacement  is 
complete.  Though  the  ferromagnesian  silicates  are,  for  the 
most  part,  directly  converted  into  the  minerals  mentioned,  they 
form  also  a  chlorite,  very  rich  in  iron,  as  an  intermediate 

*  W.  Lindgren,  Bull  Geol.  Soc.  Am.,  vol.  vi.,  pp.  221-240  ;  also  in  U.  S.  Geol 
Surv.,  14th  Ann.  Rept.,  pt.  ii.,  pp.  249  to  284,  and  17th  Ann.  Rept,  pt.  ii.,  pp.  1  to 
262. 


586 


METASOMATIC    PROCESSES    IN   FISSURE-VEINS. 


stage,  which  is  converted  later  into  sericite.  An  interlacing 
structure  of  sericite  foils,  the  triangular  or  polygonal  inter- 
stices of  which  are  filled  with  calcite  (Fig.  12),  is  often  noted. 
The  quartz  is  also  attacked,  but  with  more  difficulty ;  and  in 
no  case  is  it  completely  replaced  by  the  attacking  sericite-car- 
bonate  aggregate  (Fig.  15).  Magnetite  seems  to  be  converted 
mostly  into  ferrous  carbonate,  and  ilmenite  to  rutile.  Sharp 
cubes  of  pyrite  form  in  the  new  aggregates,  but  also  in  the 
fresh  primary  minerals.  The  only  other  sulphide  found  is 
arsenopyrite,  which,  in  some  mines,  appears  as  sharply  defined 
rhombic  crystals.  The  sulphides  sometimes  include  fibers  of 
sericite.  The  result  of  the  process  is  the  conversion  of  the 
rock  to  sericite,  carbonates,  quartz  and  pyrite,  with  retention 
of  the  original  structure  as  shown  in  Fig.  27.  The  alteration 
of  serpentine  has  already  been  referred  to. 

From  many  analyses  the  following  eight  are  selected,  A  and 
A1?  B  andB1?  etc.,  being  respectively  the  unaltered  and  altered 
rock  from  each  locality  : 

TABLE  I. — Analyses  of  Metasomatic  Rocks  from  Gold- 
Quartz  Veins. 


A. 

AI. 

B. 

BI. 

C. 

Ci. 

D. 

D!. 

SiO,        

Per 
cent. 
65.54 

Per 
cent. 
46  13 

Per 
cent. 
45.56 

Per 
cent. 
37.01 

Per 
cent. 
66  65 

Per 
cent. 
56  25 

Per 
cent. 
51  01 

Per 
cent. 

45  74 

TiO, 

.39 

.67 

1.11 

.85 

38 

25 

98 

36 

AloOo 

16.52 

15.82 

14.15 

12  99 

16  15 

17  65 

11  89 

5  29 

Fe,O,  .. 

1.40 

.89 

1.20 

.43 

1  52 

.76 

1  57 

13 

FeO  

2.49 

2.27 

9.83 

3.57 

2  36 

2  64 

6  08 

2  06 

FeS2  

1.61 

7.86 

7.99 

02 

2  87 

1  73* 

49 

Cu2S      

.10 

trace 

trace 

MnO  

.06 

.09 

.25 

.24 

.10 

none 

trace 

.26 

NiO   ZnO  

trace 

trace 

trace 

CaO  

4.88 

10.68 

2.30 

9.78 

4.53 

4.46 

10.36 

23  85 

SrO  

not  det. 

trace 

trace 

trace 

trace 

none 

none 

BaO  

not  det. 

trace 

trace 

trace 

.07 

.03 

none 

trace 

MgO.  .. 

2.52 

2.13 

6.76 

5.49 

1.74 

1.69 

8.87 

.94 

K2O  

1.95 

5.30 

1.18 

4.02 

2.65 

6.01 

.15 

1.29 

Na2O  

4.09 

.17 

1.57 

.13 

3.40 

.30 

4.17 

.11 

Li2O  

trace 

trace 

trace 

trace 



trace 

H20  below  110°  C... 
H20  above  110°  C... 
P  O= 

"*.*59 

.18 

.12 
2.42 
.10 

.23 

4.84 
.14 

.13 

1.92 
.06 

.18 
.72 
10 

.30 
2.36 
.21 

.24 
2.09 
17 

.22 

1.07 
07 

so,  

.03 

.04 

CO2          

11.24 

3.04 

15.04 

4.82 

18.91 

Total 

100.61 

99.64 

100.15 

99.69 

10057 

10060 

99  31 

10079 

*  Probably  present  as  Fe7S8. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 


587 


A,  Fresh  granodiorite,  Lincoln,  Placer  Co.  Though  not  adjoining  the  vein,  it 
indicates  closely  the  actual  composition  of  the  fresh  wall-rock.  W.  F.  Hille- 
brand,  analyst. — Ai,  Altered  granodiorite,  Plantz  vein,  Ophir,  Placer  Co.  W. 
F.  Hillebrand,  analyst. — B,  Amphibolite  schist,  Mina  Kica  vein,  Ophir,  Placer 
Co.  Fairly  fresh,  but  contains  pyrite  and  calcite.  W.  F.  Hillebrand,  analyst. — 
Bj,  Completely  altered  amphibolite  schist,  Conrad  vein,  Ophir,  Placer  Co.  W. 
F.  Hillebrand,  analyst. — C,  Fresh  granodiorite,  Nevada  City,  Nevada  Co.  W.  F. 
Hillebrand,  analyst. — C1?  Altered  granodiorite,  Belief ountain  mine,  Nevada 
City.  George  Steiger,  analyst. — D,  Fresh  diabase,  Grass  Valley.  N.  H.  Stokes, 
analyst.— D!,  Altered  diabase,  North  Star  mine,  Grass  Valley.  W.  F.  Hille- 
brand, analyst. 

From  the  chemical  and  microscopical  data  the  following 
compositions  may  be  calculated  (see  reports  cited).  The  only 
difference  from  the  sources  quoted  is  due  to  the  fact  that  by  later 
chemical  examination  the  titanium  mineral  present  has  been 
shown  to  be  rutile  instead  of  titanite. 

TABLE  II. — Mineralogical  Composition  of  the  Altered  Rocks 
of  Table  I. 


AI. 

Bi. 

Ci. 

Di. 

Per  cent. 
16.00 

Per  cent. 
24.00 

Per  cent. 
25.00 

Per  cent. 
35  00 

Sericite  (with  a  little  chlorite) 

41  76 

46  97 

61  46 

21  20 

Calcite 

17  53 

18  87 

7  23 

4°  15 

Magnesite           

9  67 

2  93 

2  70 

71 

Siderite                 

5  76 

3  67 

58 

Rhodonite       

42 

14 

• 

Kutile          

85 

.67 

25 

36 

Pyrite  

7.99 

1.61 

2  87 

50 

.13 

.22 

46 

.15 

Total  

100.11 

99  08 

100  55 

100  07 

As  it  seems  probable  that  the  alumina  has  remained  fairly 
constant  in  the  first  three  pairs  of  analyses  in  Table  I.,  they 
may  be  directly  compared  for  an  approximate  review  of  the 
chemical  changes  affected.  A  recalculation  on  the  basis  of 
constant  alumina  seemed  scarcely  worth  while. 

The  silica  has  been  in  all  cases  greatly  reduced.  Except  in 
A,  which  is  not  from  the  immediate  vicinity  of  the  vein  of  A1? 
the  titanic  acid  has  decreased.  Ferrous  and  ferric  oxide  are 
both  reduced — the  latter  more  than  the  former ;  and  the  whole 
or  a  part  of  this  loss  reappears  as  pyrite.  Lime  shows  great 
increase  except  in  C,  where  it  is  constant.  Baryta  in  C  shows 
partial  loss.  The  loss  of  magnesia  is  considerable,  except  in  C, 


588  METASOMATIC    PROCESSES   IN   FISSURE-VEINS. 

where  it  is  slight.  Potassa  is  strongly  increased  throughout ; 
and  there  is  a  corresponding  loss  of  soda. 

DL  differs  from  the  rest  in  an  exceptionally  high  percentage 
of  introduced  lime  and  carbon-dioxide,  and  a  corresponding 
loss  of  magnesia.  Moreover,  the  alumina  is  so  low  that  re- 
moval of  this  constituent  must  be  supposed  to  have  taken 
place. 

The  characteristic  features  of  the  process  seem  to  consist  in 
the  decrease  of  silica,  magnesia  and  soda,  and  increase  of  lime, 
potassa  and  carbon-dioxide — this  calcitic  altered  rock  strongly 
contrasting  with  the  quartz-filled  veins.  Sufficient  data  are  not 
available  for  the  accurate  determination  of  change  of  volume 
during  the  process,  and  of  the  actual  losses  and  gains.  They 
could  probably  be  determined  by  analyses  and  specific  gravity 
determinations  of  very  carefully  selected  samples  of  the  fresh 
rocks,  and  of  altered  rocks  immediately  adjacent  to  them.  It 
seems  probable  that,  in  most  cases,  the  added  material  has 
more  than  balanced  the  losses. 

Idaho  Types. — In  the  Rocky  Mountain  region  appear  other 
types  related  to  that  of  California.  These  gold-quartz  veins 
cut  granites,  diorites  and  various  porphyries,  and,  like  the 
California  veins,  are  of  pre-Tertiary,  probably  Cretaceous,  age. 
They  carry  a  strong  percentage  of  sulphurets,  but  generally 
only  a  subordinate  amount  of  free  gold,  most  of  the  gold  being 
closely  held  in  the  sulphides.  The  filling  constitutes  the  rich 
ore,  but  the  narrow  zone  of  metasomatic  rock  may  also  yield 
some  low-grade  ore.  In  general  character,  the  metasomatic 
action  is  similar  to  that  of  the  California  veins,  though  the  de- 
tails of  chemical  change  may  differ.  Galena,  zinc-blende  and 
chalcopyrite,  and  occasionally  also  free  gold,  may  appear  in  the 
altered  rocks.  The  carbonates  are  less  plentiful,  and  lime  is 
more  often  subtracted  than  added.  The  following  analyses  il- 
lustrate the  chemical  changes  in  two  prominent  types.  E  and 
Ex  are  the  fresh  and  altered  rock  from  Willow  Creek  district, 
Boise  county.  The  narrow  quartz-veins  carry  scarcely  any  free 
gold,  but  much  auriferous  galena,  pyrite,  arsenopyrite  and 
zinc-blende.  F  and  Fx  are  the  fresh  and  altered  rock  from  the 
Croesus  mine,  Wood  River  district,  Elaine  county.  The  nar- 
row streaks  of  filling  here  consist  of  quartz,  siderite,  pyrrhotite 
and  chalcopyrite,  with  a  little  galena,  arsenopyrite  and  zinc- 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 


589 


blende.     Here  again  only  a  fraction  of  the  gold  is  in  free  state. 
The  ore  contains  very  little  silver.* 

TABLE  III. — Analyses  of  Fresh  and  Altered  Rocks  from  Gold- 
Quartz  Veins. "\ 


E. 

Ei. 

F. 

»*. 

SiO2 

65  23 

66  66 

57  78 

58  01 

TiO2                 

.66 

49 

1.01 

1  08 

A12O3      

16  94 

14  26 

16.28 

15  72 

Fe9O, 

1.60 

.67 

1.02 

.64 

FeO  

1.91 

1  33 

4.92 

3.87 

CoO,  NiO  

.02 

none 

MnO  

trace 

trace 

.15 

.17 

CaO 

3  85 

3  37 

6  65 

2  15 

SrO                                                           

07 

none 

BaO                                                

19 

none 

12 

trace  ? 

MgO 

1  31 

95 

4  60 

2  07 

K2O         

3  02 

4  19 

2  22 

4.79 

Na.2O           

357 

none 

3.25 

.10 

H2O  below  100°  C  

.18 

36 

.34 

.31 

H2O  above  100°  C  

.88 

2  16 

.92 

2.71 

P9O-... 

.19 

.17 

.30 

.31 

CO,.  .  . 

.25 

3.67 

.15 

2.86 

s..!... 

none 

.95 

.02 

1.25 

Fe  

.84 

1.52 

Co  Ni 

12 

Pb 

.86 

Cu.                                

05 

As  

1  65 

" 

Total  

99.78 

100.07 

99.82 

100.24 

E,  Fresh  granitic  rock  immediately  adjoining  the  Silver  Wreath  quartz  vein, 
Willow  Creek,  Idaho.     E1?  Altered  rock,  adjoining  the  same  vein.     F,  Fresh 


quartz-pyroxene-diorite,  adjoining  the  Croasus  vein,  Hailey,  Idaho, 
rock  adjoining  the  same  vein. 


F,,  Altered 


The  composition  of  the  altered  rocks  may  be  calculated  as 
shown  in  table  on  page  670. 

The  appearance  of  the  altered  rock  I\  from  the  Crresus 
mine  is  shown  in  Fig.  25. 

The  specific  gravity  of  E  is  2.714.  From  the  mineralogical 
composition  given  in  the  report  quoted  the  specific  gravity  is 
calculated  to  2.720,  which  is  a  close  agreement,  the  difference 
possibly  indicating  a  very  slight  porosity.  J 

*  For  full  calculations  and  description  of  E  and  E!  see  W.  Lindgren,  18^  Ann. 
Rept.  U.  S.  Geol  Surv.,  part  iii.,  p.  640  ;  for  F  and  Fx  see  W.  Lindgren,  20th 
Ann.  Eept.  U.  S.  Geol.  Surv.,  part  iii.,  p.  211-232. 

f  Analyst,  W.  F.  Hillebrand. 

j:  In  this  calculation  the  following  figures  for  specific  gravity  are  used  :  quartz, 
2.65  ;  sericite,  2.83  ;  biotite,  3.00  ;  oligoclase,  2.65  ;  orthoclase,  2.56. 


590 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 


TABLE  IV.  —  Mineralogical  Composition  of  El  and 
Table  III. 


n 


EL 

FI. 

Quartz  

42.00 
46.84 

36.18 
38.18 
11.76 
3.11 
1.26 
2.19 
1.08 
.72 
.58 
.15 
trace 
.99 
.15 
3.58 

Sericite 

Chlorite 

Calcite 

4.80 
1.96 
1.45 
-.49 

Masrnesite 

Siderite 

Rutile 

Apatite 

Pyrite  

1.78 

Pyrrhotite 

Zinc-blende 

Galena  

Chalcopyrite 

Arsenopyrite 

Total  

99.32 

99.93 

The  measured  specific  gravity  of  E:  is  2.774,  indicating  that 
the  rock  alters  to  denser  minerals.  The  calculation  of  the 
same  specific  gravity  from  Table  IY.  gives  2.796,  which  shows 
a  decided  porosity  of  the  altered  rock.  Under  these  circum- 
stances, no  evidence  of  pressure  being  noted,  it  maybe  assumed 
with  fair  accuracy  that  no  considerable  change  in  volume  has 
taken  place ;  and  by  multiplying  the  percentages  of  E  and  E: 
by  2.714  and  2.774  respectively,  and  comparing  the  results,  the 
absolute  gains  and  losses  per  cubic  meter  may  be  obtained  (see 
Table  V.). 

In  the  same  manner  the  measured  specific  gravities  of  F  and 
Fj  are  compared  with  the  calculated  specific  gravities.*  This 
shows  that  similar  conditions  prevail  here,  the  porosity  being 
greater.  By  multiplying  the  percentages  of  F  and  Fx  by  the 
measured  specific  gravities,  and  comparing  these  data,  the  ab- 
solute gains  and  losses  are  again  obtained. 

During  the  alteration  of  E  to  Ep  291  kilograms  were  added 
and  229  lost  per  cubic  meter;  the  net  total  being  a  gain  of  62 
kilos.  During  the  alteration  of  F  to  F,,  416  kilograms  were 
added  and  333  lost  per  cubic  meter;  the  net  total  being  a  gain 
83  kilos. 

A  perusal  of  the  table  will  show  very  similar  results  in  the 


*  20*A  Ann.  Kept.  U.  S.  Geol.  Surv.,  part  iii.,  pp.  211-232. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 


591 


TABLE  Y. — Grains  and  Losses  per  Cubic  Meter  of  E  and  F, 

Table  III. 


E. 

F. 

GAIN. 

Loss. 

GAIN. 

Loss. 

Per  Cubic  Meter 
ofE. 

Percentage  of,  for 
Each  Constituent. 

Per  Cubic  Meter 
ofE. 

Percentage  of,  for 
Each  Constituent. 

Per  Cubic  Meter 
ofF. 

Percentage  of,  for 
Each  Constituent. 

Per  Cubic  Meter 
ofF. 

Percentage  of,  for 
Each  Constituent. 

SiO2   

Kilos. 
79 

Per 
cent. 
4.5 

Kilos. 

"4 
64 
24 
15 

Per 
cent. 

22.2 
13.9 

55.8 
28.8 

Kilos. 
48 

2 

Per 
cent. 
2.9 
6.9 

Kilos. 

*4 
10 
27 
1 

126 
2 

4 
70 

89 
"6 

Per 
cent. 

'".9 
34.5 
19.4 
100.0 

67.0 
100.0 
100.0 
53.9 

96.7 

TiO2  

ALOo... 

FeO... 

FeO..  

CoO  NiO 

MnO 

1 

25.0 

CaO 

11 

10.5 

SrO. 

BaO       .           

5 

9 

97 
"6 

100.0 
25.7 

100.0 

76 

53 

0 
79 

35 

44 

4 
24 

2 
48 

120.6 
203.8 

nearly 
all. 
nearly 
all. 
all. 
all. 
all. 
all. 
all. 

MO.    . 

K2O    

34 

41.5 

Na/)     

H2O  above  105°  C  

36 
0 
93 

26 
23 

150.0 

nearly 
all. 
all. 

all. 

RXX... 

CO.,..,    

s                 ..   .. 

Fe               

Co  Ni  

Pb  

Cu  

As  

Total 

291 

229 

416 

333 

two  rocks :  a  moderate  addition  of  silica  and  a  strong  gain  of 
potassa;  nearly  complete  loss  of  soda,  baryta  and  strontia; 
partial  loss  of  alumina,  magnesia  and  lime,  F,  however,  losing 
much  more  lime  than  E.  In  Et  the  amounts  lost  of  Fe203  and 
FeO  are  nearly  completely  converted  into  Fe  (in  FeS2).  In  F 
these  losses  are  less  and  not  sufficient  to  account  for  the  gain  of 
Fe;  consequently  iron  must  have  been  added.  Phosphoric 
acid  is  constant,  consistently  with  the  fresh  state  of  the  apatite. 
San  Juan,  Colorado. — In  the  San  Juan  region,  southwestern 
Colorado,  are  vast  eruptive  masses  of  andesites  and  rhyolites, 


592  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

with  their  accompanying  tuffs  and  breccias.  Some  of  the  gold- 
quartz  veins  of  Tertiary  age  occurring  in  these  rocks  at  Tellu- 
ride  have  been  described  by  Mr.  C.  W.  Purington.*  The  ores 
consist  of  quartz  containing  native  gold,  with  pyrite,  galena  and 
other  sulphides.  In  some  localities  silver  is  also  present  in  con- 
siderable amount.  The  principal  gangue  is  quartz,  though  car- 
bonates also  are  occasionally  present,  and  fluorite  in  consider- 
able quantities  is  mentioned  from  the  Tomboy  vein.  This  is 
worthy  of  note ;  since,  in  ordinary  gold-quartz  veins  fluorite, 
if  not  entirely  absent,  at  least  is  exceedingly  rare.  The  quartz 
forms,  as  a  rule,  a  well-defined  filling  of  open  cavities,  and  the 
principal  ore  is  of  this  character,  and  not  altered  country-rock. 
There  are,  however,  more  or  less  wide  zones  of  partial  altera- 
tion alongside  the  veins.  The  veins  are  often  accompanied  by 
large  amounts  of  white,  soft  clay-like  material,  which  probably 
is  extremely  altered  country-rock.  All  of  this  appears  to  be 
sericite.  Mr.  Purington  mentions  having  failed  to  establish  the 
presence  of  kaolinite,  except  in  one  or  two  places.  The  ordi- 
nary course  of  alteration  in  the  diorites,  andesites  and  breccias 
is  distinguished  by  the  development  of  much  calcite  and  seri- 
cite, and  is  consequently  very  similar  to  the  metasomatic  pro- 
cesses characterizing  the  California  quartz-veins.  The  altered 
rocks  contain  small,  abundant  and  sharply  defined  crystals  of 
pyrite,  more  rarely  of  galena.  Much  of  this  pyrite  fills  the 
spaces  formerly  occupied  by  ferro-magnesian  silicates.  This 
pyrite  is  of  low  value,  compared  with  the  massive  mineral  oc- 
curring in  the  vein-filling.  The  percentage  of  silica  in  the  al- 
tered rock  is  low,  and  contrasts  with  the  abundant  quartz  on 
the  veins. 

Rhyolite  adjoining  the  veins  is  changed  to  felted  sericite  and 
some  carbonates,  as  well  as  pyrite. 

As  an  exceptional  process  Mr.  Purington  mentions  a  complete 
silicification  of  the  diorite  from  the  hanging-wall  of  the  Butter- 
fly vein,  in  the  Terrible  mine.  This  diorite,  which  consists  of 
labradorite,  hornblende  and  a  little  biotite,  shows  a  complete 
replacement  of  the  feldspar  by  cryptocrystalline  silica,  while 
the  hornblende  is  replaced  by  pyrite.  There  is  a  little  sericite, 
but  no  carbonate  present.  The  cause  of  this  abnormal  altera- 

*  18th  Ann.  R&pt.  U.  S.  Geol  Surv.,  part  iii.,  pp.  745-846. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  593 

tion  might  be  in  a  local  occurrence  of  waters  in  which  the  H2S 
had  been  oxidized  to  H2S04.  A  partial  analysis  of  the  silicified 
diorite  runs  as  follows  : 

Per  cent. 
SiO2.      .        .      *V    *'.'"*'•'."'"'  V^'  •'"'"  ''•'"'  '  •.  '  .•        •     70.30 

Ai2o3,*.  "•'••  ;-  ••'  '  ••-  :  •*  ;  ^  .^  -f;;  l  .'-'•  ••."•'•  .  '   .   20.00 

MgO,     .  -..     ,  .  .  :'•  :,*  i  ...  i  *-  *        ..     ;  .  .  0.31 

CaO,      .  "  .        .  .        ,  .'.      .  .'..*•-..  .  0.27 

K20,      .        .       ',  .        '..  V  '    .  .      '  .       ".  .  1.78 

.        ."'.-.-  '.    :-;.  .  '.'  .       'r'^1-  .  0.64 


The  large  percentage  of  alumina  indicates  the  presence  of 
kaolinite,  so  commonly  accompanying  silicification.  Sericite  is 
also  present. 

A  further  instance  of  silicification  in  part,  probably,  due  to 
cementation,  is  mentioned  in  the  case  of  certain  sedimentary 
rocks  adjoining  the  vein.  Here  again  it  is  accompanied  by  a 
development  of  pyrite  ;  and  the  silicification  extends  to  a  dis- 
tance of  15  feet  from  the  vein. 

The  Treadwell  Mine,  Alaska.  —  According  to  G.  F.  Becker,f 
the  country-rock  of  the  celebrated  Treadwell  mine  consists  of 
a  sodium  syenite,  which  is  strongly  altered  and  traversed  by 
small  seams,  carrying  a  value  chiefly  in  gold.  The  whole  mass 
of  seams  and  country-rock  is  mined  and  milled.  The  process  of 
alteration  consists  in  a  change  of  the  albite,  which  is  the  pre- 
dominant mineral,  into  carbonates  and  pyrite.  Sericite  is  also 
present,  as  well  as  a  little  chlorite. 

Gold-  Veins  of  Ontario,  Canada.  —  Peter  McKellarJ  describes 
quartz-veins  in  granite  of  Western  Ontario  at  Lake  of  the  Woods, 
which  are  supposed  to  be  of  Archean  age.  The  quartz-veins 
are  only  from  3  to  4  in.  wide  containing  auriferous  sulphides 
of  copper,  lead,  zinc  and  bismuth.  These  narrow  veins  are 
adjoined  by  from  2  to  5  ft.  of  altered  granite,  largely  consisting 
of  a  greenish  fine-grained  mineral,  probably  sericite.  Some  of 
this  altered  granite  contains  gold,  and  from  0.5  to  3  per  cent. 
of  auriferous  pyrite,  while  the  above  mentioned  sulphides  rarely 
appear  in  it.  The  principal  ore  consists  of  this  altered  rock. 

Schwarzwald  Fissure-  Veins.  —  Much  material  of  interest  relat- 
ing to  the  alteration  of  country-rock  is  found  in  the  well-known 

*  Including  Fe2O3,  TiO2,  and  P2O5. 

f  18th  Annual  Report  U.  S.  OeoL  Surv.,  part  iii.,  p.  64. 

%  Trans.,  xxix.,  104  (1899). 


594  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

investigations  of  Prof.  Sandberger.*  In  his  discussions,  as 
may  be  expected,  superficial  weathering  is  not  always  strictly 
separated  from  deep-seated  alteration.  In  the  fissure-veins  of 
Schapbach,  in  the  Schwarzwald,  biotite  of  the  granitic  country- 
rock  yields  a  chlorite  rich  in  iron  and  a  substance  supposed  to 
be  pilite.  The  decomposition  (alteration  ?)  of  the  gneiss  in  the 
same  districts  yields  a  mineral  which  Sandberger  calls  hy- 
grophilite,  derived  from  the  alteration  of  oligoclase.  It  has  a 
specific  gravity  of  2.70,  and  is  closely  allied  to  muscovite,  if 
not  identical  with  it.  The  alteration  of  the  schistose  gneiss 
near  the  veins,  involving  a  formation  of  hygrophilite  from  oli- 
goclase, shows  a  concentration  of  K20  and  a  decrease  of  Na20. 
In  one  instance  a  conversion  to  carbonates  was  also  noted.  For 
a  certain  distance  on  both  sides  of  the  veins  the  rock  is  soft- 
ened and  altered.  The  extent  of  this  alteration,  which  is  sup- 
posed to  be  favorable  to  the  occurrence  of  rich  ore-bodies,  cor- 
responds to  the  extent  over  which  its  principal  leaching  has 
taken  place.  Sandberger  thus  derives  the  minerals  of  his  veins 
directly  from  the  adjoining  country-rock.  He  further  says  :f 

"It  is  of  the  greatest  importance  for  the  understanding  of  the  veins  occur- 
ring in  this  granite  area  to  examine  the  alterations  which  the  rock  has  suffered  by 
means  of  waters  containing  carbonic  acid,  and  by  means  of  weathering  with  free 
access  of  atmospheric  oxygen." 

In  the  silver-veins  of  Wittich,  Schwarzwald,  Prof.  Sandber- 
ger finds  that  the  alteration  of  the  biotite  is  accompanied  by 
the  separation  of  Ti02  as  anatase  or  brookite.  The  oligoclase 
is  transformed  to  a  kind  of  pinitoid  which  Sandberger  calls 
lepidomorphite,  and  which  may  simply  be  an  impure  and  mi- 
crocrystalline  muscovite.  Two  analyses  are  givenj  of  fresh 
and  altered  granite,  the  latter  occurring  close  to  a  vein.  The 
composition  of  the  altered  rock  is  almost  the  same  as  that  of 
the  fresh,  except  that  a  little  iron,  somewhat  over  one  per  cent, 
of  lime,  and  an  equal  amount  of  magnesia,  have  been  carried 
away.  The  potash  remains  practically  constant,  while  about 
one-half  per  cent,  of  soda  has  been  lost.  The  silica  has  suf- 
fered an  increase  of  2.5  per  cent.,  the  alumina  of  1  per  cent. 
Sandberger  remarks  with  good  reason  that  these  slight  changes 


*   Untersuchungen  ilber  Erzg'dnge,  i.  and 
f  Op.  cit.,  ii.,  p.  343. 


ii. 


Op.  cit.,  ii.,  p.  347. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  595 

could  very  well  have  been  effected  by  waters  containing  a  little 
carbon  dioxide. 

Near  the  vein  of  Wittichen  the  ore-minerals  are  not  confined 
to  the  fissure,  but  are  also  present  to  a  remarkable  extent  in  the 
altered  rock  adjoining  it.  The  gangue  is  here  quartz,  barite, 
calcite  and  fluorite.  The  ores  consist  of  native  silver  and  vari- 
ous cobalt-minerals.  The  ore-minerals  mentioned,  accompanied 
by  small  crystals  of  chalcopyrite,  occur  abundantly  in  the 
altered  granite.  The  veins  traverse  not  only  the  granite  but 
also  the  overlying  Permian  formation,  although  in  these  hori- 
zontal rocks  they  lose  their  mineral  contents  almost  completely. 
They  are  rich  only  in  the  altered  granite,  the  oligoclase  and 
mica  of  which  have  been  completely,  and  the  orthoclase  par- 
tially altered.  It  is  acknowledged  that  these  veins  were  formed 
when  1500  feet  of  rocks  rested  on  the  granite,  and  that  conse- 
quently the  temperature  and  pressure  must  have  been  higher 
than  at  the  surface.  In  conformity  with  Prof.  Sandberger's 
well-known  views,  the  sulphides  occurring  on  the  veins  are  ex- 
plained by  reduction  of  sulphates. 

The  veins  of  Schapbach  may  be  compared  with  those  de- 
scribed from  the  Central  Plateau  of  France  by  Daubree.  The 
similarity  in  occurrence,  gangue  and  ores  is  very  striking; 
only,  in  the  case  of  the  latter  we  have  undoubted  proof  of  their 
intimate  connection  with  actual  ascending  springs. 

9.  Silicic  and  Caldtic  Cinnabar-  Veins. 

The  quicksilver-deposits  of  the  Pacific  Coast  have  been  de- 
scribed by  GL  F.  Becker.*  The  cinnabar  occurs  chiefly  in 
zones  of  fracture  or  in  fissure-veins,  and  is  almost  always  asso- 
ciated with  quartz  and  chalcedonic  aggregates.  Opal  is  very 
commonly  present  in  the  ores,  but  the  sulphide  of  mercury  is 
very  rarely  if  ever  directly  imbedded  in  it.  The  main  deposit 
of  opal  preceded  that  of  cinnabar  and  quartz. 

Various  rocks,  such  as  diabase,  diorite  and  serpentine,  are 
adjacent  to  the  quicksilver-veins.  These  rocks  are  nearly 
always  more  or  less  altered  and  converted  into  dolomitic  car- 
bonates. Many  of  them  are  also  silicified,  being  converted  into 
opal.  Serpentine  especially  is  often  transformed  in  this  man- 

*  Monograph  XIII.,  U.  S.  Geol.  Surv. 
38 


596  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

ner,  and  all  transitions  between  the  fresh  rock  and  the  pure 
opal  may  be  found ;  the  latter  may  retain  the  color  and  struc- 
ture of  serpentine.  Certain  glaucophanes  from  the  Lake 
Quicksilver  mine  are  altered  into  microcrystalline  quartz. 
Although  Mr.  Becker  recognizes  the  fact  that  the  country-rock 
has  been  altered  by  carbonization  and  silicification,  he  insists 
that  the  cinnabar  has  been  exclusively  deposited  in  open  spaces, 
and  does  not  appear  as  a  product  of  direct  replacement  of  the 
wall-rock.  The  quicksilver-deposits  are  of  special  interest,  be- 
cause their  intimate  connection  with  ascending  alkaline  waters 
has  been  proved.  These  waters  contain  but  little  free  carbon 
dioxide,  earthy  carbonates  and  earthy  sulphates,  but  consider- 
able sodic  bicarbonate  and  sodic  chloride,  and  some  hydrogen 
sulphide. 

10.  Sericitic  Copper-Silver  Veins. 

The  copper-veins  of  Butte,  Montana,  which  have  been  de- 
scribed by  Emmons,  Weed  and  Tower,*  form  an  excellent  illus- 
tration of  this  class  and,  according  to  Mr.  Emmons,  are  typical 
replacement-veins.  The  deposits  appear  along  well-defined  fis- 
sures in  granitic  rocks ;  the  principal  gangue-mineral  is  quartz, 
the  primary  ores  are  pyrite,  chalcopyrite,  zinc-blende  and 
galena.  Bornite,  chalcocite  and  covellite  are  regarded  as  sul- 
phides formed  later  under  secondary  influences.  In  the  vicinity 
of  the  veins  the  country-rock  is  impregnated  with  vein-mate- 
rial, generally  pyrite  and  quartz.  An  impregnation  of  enar- 
gite  has  also  been  observed.  Sericite  and,  later,  kaolin  have 
also  been  developed  in  the  rock.  The  extent  of  the  altered 
zone  is  generally  proportional  to  the  size  of  the  ore-bodies,  and 
may  extend  to  a  distance  of  100  feet  from  the  vein.  According 
to  the  proportion  of  copper  in  such  an  altered  mass  it  may  con- 
stitute pay-ore  or  be  considered  as  barren  material. 

11.  Silicic  and  Dolomitic  Silver-Lead  Veins. 

The  association  of  silver-lead  deposits  with  limestone  and 
other  calcareous  sedimentary  rocks  is  a  well-known  fact,  occur- 
ring again  and  again  in  all  parts  of  the  world.  Very  many  of 
these  deposits  are  not  fissure-veins,  or  connected  with  such. 
But  even  among  those  genetically  related  to  fissures,  the  ores 

*  Folio  38,  U.  S.  Glol.  Surv. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  597 

seldom  form  well-defined  tabular  masses,  but  occur  mostly  as 
irregular  bodies,  while  the  ducts  through  which  the  solutions 
found  access  have  received  but  scanty  deposits  of  ore.  This  is 
due  to  the  great  tendency  of  galena  and  zinc-blende,  which  in 
these  deposits  form  the  principal  ore-minerals,  to  replace  the 
limestone.  Beyond  doubt  such  a  replacement  very  often  occurs. 
It  was  convincingly  established  by  Mr  Emmons  in  Leadville, 
Colo.,  and  by  Mr.  Curtis  in  Eureka,  Nev.  In  both  these 
cases  the  demonstration  was  furnished  by  the  study  of  struc- 
tural relations,  without  the  aid  of  microscopic  examination. 
Indeed,  the  latter  was  scarcely  possible,  since  in  both  these 
mining  districts  operations  were  still  in  the  zone  of  oxidation, 
which  obscured  the  relations  of  primary  ore-minerals  to  the 
limestone.  Since  these  reports  were  published,  the  conditions 
governing  the  replacement  of  the  galena  have  not  been  greatly 
elucidated,  except  in  Spurr's  study  of  the  Aspen  district.  The 
chemical  reactions  involved  were,  and  are  yet,  in  some  doubt ; 
the  principal  question  being  whether  the  galena  was  reduced 
from  solution  of  sulphate  of  lead  or  deposited  from  sulphide  so- 
lution (see  p.  617).  The  microscopic  study  of  the  attending 
phenomena  must  help  to  settle  this  point. 

The  ores  are  accompanied  either  by  a  gangue  of  jasperoid, 
cherty  rocks  chiefly  composed  of  silica,  or  by  different  carbon- 
ates, such  as  calcite,  dolomite  or  siderite.  (Those  accompanied 
by  a  siderite  gangue  will  be  treated  as  a  separate  class.) 
Sericitic  minerals  are  absent.  The  gangue-minerals  mentioned 
have  also  very  largely  replaced  the  limestone. 

In  the  Elkhorn  mine,  Mont.,  studied  by  W.  H.  Weed,* 
bodies  of  galena  appear  in  a  crystalline  limestone  and  are  di- 
rectly connected  with  a  fissure-vein.  The  beginnings  of  replace- 
ment are  shown  in  specks  of  intergrown  galena  and  pyrite,  scat- 
tered through  the  rock,  and  always  accompanied  by  small 
crystals  of  secondary  quartz.  The  larger  grains  of  galena  are 
surrounded  by  a  narrow  rim  of  pyrite  (see  page  617  and  Fig. 
29). 

Mr.  Emmons  describes  the  fissure-vein  of  the  Queen  of  the 
West  mine,  Ten  Mile  district, f  Colorado.  The  principal  fissure 
is  partly  filled  with  barren  calcite,  while  galena  and  blende  re- 

*  Unpublished  notes.  f  Folio  48,  U.  S.  Geol.  Surv. 


598  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

place  the  country-rock,  consisting  of  sandstone  and  intercalated 
sheets  of  porphyry.  The  vein  is  characterized,  besides,  by  a 
number  of  parallel  fault-planes,  from  which  replacement  has 
taken  place. 

Aspen,  Colorado. — Mr.  Spurr,  in  his  description  of  the  Aspen 
district,*  with  its  wonderfully  complicated  system  of  faults,  has 
given  a  valuable  description  of  the  metasomatic  processes  there 
observed.  The  Aspen  deposits  are  not,  strictly  speaking,  fis- 
sure-veins. The  ores  form  irregular  bodies  of  lead-  and  silver- 
minerals  in  limestone ;  but  these  irregular  bodies  are  closely 
connected,  genetically,  with  faults  which  yielded  a  pathway  for 
the  ascending  waters.  The  processes  consist  in  dolomitization, 
ferration,  silicification,  and  lastly,  the  introduction  of  metallic 
sulphides.  The  ores  occur  in  part  as  filling  of  pre-existing 
cavities,  but  more  generally  replace  the  limestone  adjoining  the 
fissures.  The .  dolomitization  which  proceeds  irregularly  from 
the  fissures  is  well  shown  under  the  microscope,  the  coarse  cal- 
cite  being  broken  up  into  smaller  rhombohedral  crystals  of  the 
yellowish  tinge  characteristic  of  dolomite.  Silicification  usually 
accompanies  dolomitization.  In  the  limestones  the  process  goes 
on  in  the  following  manner.  Many  tiny  quartz-grains  first  ap- 
pear scattered  through  the  rock,  chiefly  along  areas  of  slight 
shearing  or  fracture  (Fig.  3).  Here  and  there  appear  long  slen- 
der quartz  crystals,  entirely  surrounded  by  fresh  limestone.  As 
silicification  proceeds,  the  slender  crystals  multiply,  forming  a 
characteristic  network,  sometimes  enclosing  small  areas  of  cal- 
cite  which  are  sprinkled  with  small,  irregular  quartz-grains, 
down  to  the  most  minute  dimensions.  The  final  result  is  a 
rock  made  up  of  crystalline  quartz-grains  of  varying  size,  in 
which  the  retiform  structure  is  still  apparent  (Fig.  4),  and 
which  rock  resembles  a  chert  or  a  fine-grained  and  altered 
quartzite,  and  is  generally  somewhat  porous,  drusy,  and  also 
often  colored  red  or  yellow.  In  structure,  appearance  and  ori- 
gin, this  cherty  rock  is  identical  with  the  jaspers  of  Lake  Supe- 
rior. Mr.  Spurr  proposes  "jasperoid"  as  a  term  for  this  rock, 
consisting  essentially  of  cryptocrystalline,  chalcedonic  or  phan- 
ero-crystalline  silica  formed  by  the  replacement  of  other  rocks, 
chiefly  limestone.  At  Aspen  this  jasperoid  forms  big  reefs 
along  fault-lines. 

*  J.  E.  Spurr,  Monograph  XXXI. ,  U.  S.  Oeol  Surv. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  599 

Dolomitization  and  silicification  are  always  accompanied  by 
a  certain  amount  of  ferration.  Usually  the  iron  appears  in  the 
partly  silicified  rocks  as  small  rhombohedrons  of  siderite ;  but 
pyrite  is  also  present,  and  in  many  cases  the  two  minerals  have 
been  deposited  simultaneously. 

In  the  final  process  of  mineralization,  the  altered  limestone 
is  always  traversed  by  reticulated  fractures.  In  every  case  the 
ores  are  first  introduced  along  these  crevices ;  and  often  this  is 
the  only  method  of  mineralization.  With  greater  alteration, 
metallic  minerals  penetrated  from  the  fractures  into  the  rock 
on  both  sides.  The  solutions  traveled  between  adjacent  crys- 
tals of  calcite  or  dolomite,  and  also  along  the  cleavage-planes 
of  these  minerals.  In  this  manner  a  still  finer  network  was 
formed,  which,  by  spreading  and  consolidation,  resulted  in  a 
continuous  mass  of  sulphides.  There  is  no  doubt,  Mr.  Spurr 
says,  that  this  is  an  actual  process  of  replacement ;  the  calcite 
or  dolomite  being  taken  up,  molecule  by  molecule,  and  replaced 
by  metallic  minerals.  The  sulphides  are  often  accompanied  by 
granular  quartz  and  dolomite,  the  relations  of  which  show  that 
they  have  been  simultaneously  deposited. 

12.  Sideritic  Silver-Lead  Veins. 

In  this  class,  which,  like  the  preceding,  ordinarily  occurs  in 
sedimentary  rocks,  not  much  secondary  silica  is  formed.  The 
principal  gangue-mineral  is  siderite,  often  accompanied  by  other 
carbonates,  and  nearly  always  also  with  some  pyrite ;  in  fact 
the  co-existence  of  pyrite  (often  also  marcasite)  and  siderite  is 
a  notable  feature.  The  other  principal  ores  are  galena  and 
zinc-blende.  The  Eureka,  Nev.,  deposits  probably  belong  to 
this  type. 

Wood  River,  Idaho. — Prominent  representatives  of  this  class 
are  the  Wood  river  silver-lead  veins,  near  Hailey,  Idaho,* 
which  occur  chiefly  in  calcareous  carboniferous  shale,  and  are 
of  pre-Miocene  age.  In  the  structure  of  the  vein  and  arrange- 
ment of  the  ore-bodies  replacement  is  clearly  indicated ;  and 
galena  often  occurs  as  scattered  grains  throughout  the  shale. 
But  some  filling  of  pre-existing  cavities  has  also  taken  place. 

The  rocks  clearly  contain  much  organic  material ;  and  the 
theory  of  deposition  by  the  reduction  of  lead  sulphate  is  pos- 

*  W.  Lindgren,  20th  Ann.  Rept.  U.  S.  Geol  Surv.,  part  iii.,  pp.  190  to  231. 


600  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

sibly  applicable.  But  this  argument  is  greatly  weakened  by 
the  occurrence  of  veins  of  the  same  composition  in  a  neighbor- 
ing body  of  granite. 

Cosur  d'Alene  Mountains,  Idaho. — There  exist,  perhaps,  no 
better  instances  of  metasomatic  fissure-veins  than  the  celebrated 
silver-lead  deposits  of  the  Coeur  d'Alene  mountains,  in  Northern 
Idaho.  They  are  clearly  defined  fissure-veins  cutting  fine- 
grained greenish  quartzites  and  quartzitic  slates  of  doubtful 
(though  probably  Algonkian)  age.  The  principal  ores  are 
galena  and  zinc-blende,  but  there  is  also  much  finely  distributed 
pyrite.  Chalcopyrite  is  ordinarily  absent.  These  are  prac- 
tically the  only  metallic  minerals,  and  recur  in  all  the  deposits. 
The  principal  gangue-mineral  is  siderite,  accompanied  by  minor 
quantities  of  quartz  and  barite.  Fluorite  is  absent.  The  fis- 
sures along  which  the  ore-bodies  appear  are  well  defined,  and 
sometimes  continuous  for  one  or  more  miles.  The  ore-bodies 
do  not  show  much  clearly  defined  crustification  or  other  evi- 
dence of  having  been  deposited  in  open  spaces.  The  siderite 
appears  always  as  an  undoubted  product  of  replacement,  while 
many  veinlets  of  quartz  have  in  part  resulted  from  the  filling 
of  open  small  fissures.  Evidences  of  gradual  transitions  from 
ore  to  country-rock  are  abundant,  and  are  especially  prominent 
in  the  mines  carrying  low-grade  ore,  as,  for  instance,  in  the 
Helena  and  Frisco.  In  the  exposures  underground,  as  well  as 
in  the  specimens  and  thin  sections,  the  evidence  of  replacement 
is  complete  and  positive. 

The  greenish-grey  fine-grained  quartzite,  which  constitutes 
the  prevailing  country-rock,  contains  no  sulphides  when  fresh. 
It  is  composed  of  small,  rounded,  or  subangular  quartz  grains, 
closely  packed — often,  indeed,  jointing  closely,  as  in  a  normal 
quartzite.  Usually,  however,  a  little  sericite,  in  bunches  of 
small  fibers,  is  present  as  cementing  material  between  the 
grains.  This  sericite  is  apparently  an  autogenetic  mineral, 
formed  during  the  metamorphism  of  the  sandstone  to  a  quartz- 
ite. Occasionally  small  foils  of  it  project  into  the  quartz,  show- 
ing a  slight  incipient  sericitization  of  the  latter  mineral.  There 
are  few  other  minerals,  except  a  little  feldspar  in  clastic  grains, 
small  prisms  of  tourmaline,  and  some  grains  of  calcite.  Near 
the  veins  minute  specks  of  siderite,  zinc-blende,  pyrite  and 
galena  appear  in  this  quartzite;  and  these  scattered  grains 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  601 

gradually  merge  into  bodies  containing  3  per  cent,  and  more 
of  galena,  thus  forming  a  merchantable  ore.  The  thin  sections 
show  how  the  rock  near  the  veins  is  filled  with  small  grains  of 
branching  and  irregular  form,  which  consist  of  siderite,  de- 
veloped by  attack  first  upon  the  ground-mass  and  then  upon 
the  grains  of  clastic  quartz.  This  process  is  well  shown  in 
Fig.  16,  which  is  reproduced  from  a  thin  section  of  Helena  and 
Frisco  country-rock.  Accompanying  the  siderite  are  small 
grains  of  zinc-blende,  cubes  of  pyrite  and  irregular  wiry  masses 
of  galena.  All  these  sulphides  appear  not  only  in  or  near  the 
siderite,  but  also  in  the  cementing  sericite,  and  in  the  apparently 
perfectly  fresh  quartz  grains. 

At  a  more  advanced  stage  (Fig.  17)  these  areas  of  siderite 
extend  until  they  join,  and  thus  completely  replace  the  rock. 
In  the  specimen  from  which  Fig.  17  was  taken,  masses  of  sid- 
erite are  seen  to  be  merging  gradually  into  the  fresh  quartzite. 
In  the  resulting  ore  lie  scattered  many  small  quartz  grains, 
representing  remnants  of  the  clastic  constituents  of  the  quartz- 
ite. Occasionally  larger  masses  of  zinc-blende  appear  to  form 
directly  in  the  quartzite  by  metasomatic  replacement  of  the 
quartz.  The  sericite  in  the  quartz  then  disappears,  though 
once  in  a  while  small  foils  of  it  may  be  detected.  During  the 
transition  stage,  seams  and  narrow  veinlets  in  the  altering  rock 
are  filled  with  sericite,  apparently  segregated  there,  when  driven 
out  from  the  main  mass.  In  other  specimens  from  the  Helena 
and  Frisco  mine,  the  replacing  siderite  has  a  strong  tendency 
to  idiomorphic  development.  Imperfect  rhombohedral  forms 
are  often  seen,  sometimes  cutting  straight  across  the  clastic 
grains  (Fig.  18).  Certain  specimens  from  the  Bunker  Hill  and 
Sullivan  mine  show  quartzose  greyish  masses  of  irregular  out- 
line, and  apparently  merging  gradually  into  the  normal  green- 
ish quartzite.  These  quartzose  masses  consist  of  very  irregular 
interlocking  grains  of  quartz,  not  in  the  least  similar  to  the 
quartz  usually  deposited  by  processes  of  filling,  but  having 
every  appearance  of  resulting  from  the  silicification  of  the 
quartzite.  This  silicified  portion  contains  irregular  grains  of 
pyrite,  galena  and  brown  zinc-blende,  with  a  very  little  siderite. 

The  process,  as  outlined,  is  remarkable,  as  involving  a  meta- 
somatic replacement  of  quartz  by  siderite,  pyrite,  galena  and 
zinc-blende,  and  is  the  only  clearly  defined  occurrence  of  this 
kind  of  which  I  am  aware. 


4302  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

This  description  would  not  be  complete  without  mention  of 
certain  interesting  veinlets  produced  by  replacement  in  the 
Bunker  Hill  and  Sullivan  quartzite.  Certain  specimens  from 
this  mine  show  a  dark  greyish-green,  very  fine-grained  quartz- 
ite, traversed  by  minute  veinlets,  carrying  quartz  and  sur- 
rounded "by  a  greenish  material.  Under  the  microscope  the 
rock  is  seen  to  be  a  typical  fine-grained  quartzite  or  quartzitic 
sandstone.  The  grains  are  separated,  not  only  by  fibers  of 
muscovite,  but  also  by  a  green  mica,  probably  related  to  bio- 
tite.  The  veinlets  are  clearly  formed  by  replacement  along 
narrow  cracks,  and  contain  a  mass  of  green  mica  in  fine  dis- 
tribution, diminishing  away  from  the  seam,  together  with 
quartz,  garnet,  brown  zinc-blende,  and  small  prisms  of  tourma- 
line, and  a  small  quantity  of  galena.  I  have  mentioned  these 
peculiar  products  of  replacement  because  they  differ  so  com- 
pletely from  the  deposits  as  described  above.  Their  formation 
must  be  sought  in  some  local  cause,  involving  a  change  in  the 
mineral-bearing  solutions,  or  in  the  conditions  of  the  deposi- 
tion. The  presence  of  garnet  in  these  veinlets  is  especially  re- 
markable, as  this  mineral  rarely  occurs  in  fissure-veins. 

13.  Sericitic  Lead-Silver  Veins. 

The  dausthal  Veins. — The  alterations  produced  in  the  clay 
slates  adjoining  the  vein-system  of  Clausthal  have  been  de- 
scribed by  v.  Groddeck.*  The  fissure- veins  at  Clausthal,  which 
principally  carry  galena,  pyrite  and  zinc-blende  in  quartzose 
gangue,  are  enclosed  in  black  clay  slate  belonging  to  the  Culm 
formation ;  and  to  the  eye  these  slates,  when  enclosed  in  the 
vein  or  lying  close  to  it,  ordinarily  present  no  alteration,  except 
such  as  may  result  from  mechanical  deformation  or  crushing. 
By  a  series  of  analyses,  v.  Groddeck  has  shown  that,  as  a  mat- 
ter of  fact,  these  wall-rocks  have  suffered  alteration  consider- 
able in  degree,  although  not  apparent  to  the  eye.  Some  aver- 
age analyses  are  given  in  Table  VI. 

Comparing  the  first  two  analyses,  it  is  apparent  that  a  large 
part  of  the  protoxide  of  iron  has  been  carried  away,  and  that 
at  the  same  time  the  magnesia  has  been  considerably  reduced. 
These  subtractions  result  in  an  apparent  increase  of  the  other 

*  "  Studien  iiber  Thonschiefer,  Gangthonschiefer  und  Sericitschiefer." 
buck  der  konigl.  preuss.  geol  Landesanstalt,  1885,  pp.  1  to  53. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 


603 


TABLE  VI. — Analyses  of  Clausthal  Hocks. 


I. 

II. 

III. 

SiO2       

Per  cent. 
56.59 

Per  cent. 
59.31 

Per  cent. 
79  12 

A1,O« 

23.14 

23.72 

13  93 

Fe9O,  . 

.61 

1.13 

.44 

Feo!..:.:  

4.87 

1.06 

MnO  

MgO..., 

1.80 

1.11 

CaO 

35 

.36 

K,O 

3  05 

3.91 

3  18 

Na2O 

75 

.80 

64 

H2O 

4.01 

4.60 

1  56 

Rutile 

38 

.23 

not  dt 

Carbon 

.64 

.95 

not  dt 

Pyrite 

.67 

.85 

not  dt 

Apatite.      .           ...       ... 

.14 

not  dt 

Carbonates  

2.56 

2.02 

1  60 

I.  Black  normal  clay  slate  of  the  Culm  formation.  Average  of  three  analy- 
ses.— II.  Black  clay  slate  adjoining  the  vein  or  enclosed  in  it.  Average  of  seven 
analyses.  These  black  altered  clay  slates  are  always  present  in  or  along  the 
veins. — III.  Variegated  clay  slate  adjoining  the  vein.  Average  of  four  analyses. 
These  variegated  slates  are  apparently  extreme  forms  of  alteration,  and  are  con- 
spicuous by  means  of  their  red  or  yellow  color.  It  is  remarked,  however,  that 
this  form  of  alteration  is  an  unusual  one,  only  appearing  locally  in  a  few  mines. 
The  processes  to  which  these  altered  rocks  have  been  subjected  are  considered  to 
have  been  different  in  kind  from  those  producing  the  ordinary  black  altered 
slates. 

constituents.  Very  notable  is  the  fact  that  the  alkalies  remain 
nearly  constant,  and  that  no  soda  has  been  subtracted — a  most 
unusual  case.  The  lime,  rutile,  carbon,  pyrite  and  carbonate 
have  suffered  but  little  change.  The  amount  of  alumina  is 
almost  identical  in  the  two  analyses;  and  on  the  assumption 
that  this  constituent  has  remained  constant,  the  two  analyses 
can  be  directly  compared. 

Comparing  the  first  with  the  third,  a  very  strong  increase  in 
silica  and  decrease  in  alumina  is  noted,  accompanied  by  an 
almost  complete  disappearance  of  the  protoxide  of  iron,  mag- 
nesia and  lime,  the  alkali  apparently  remaining  practically  con- 
stant. It  is  clear  that  the  alumina  has  been  carried  away  to  a 
considerable  extent,  and  the  process  is,  on  the  whole,  similar 
to  the  alteration  which  results  from  the  action  of  the  solutions 
containing  free  sulphuric  acid  on  aluminous  rocks.  Sericite 
and  chlorite  form  part  of  the  fresh  rock,  and  the  former  is  a 
prominent  constituent  of  the  altered  rocks.  Basing  the  calcu- 
lations on  the  following  formulae  : 


604  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

Sericite,  2H20  +  (K,  ~Na2  Ca)  0  +  3  (Fe  Al)2  03  +  6Si02, 
and 

Chlorite,  4H20  +  5  (Mg  Fe)  0  +  A12  0,  +  3Si02, 

and  disregarding  the   small  amounts  of  carbonate,  pyrite,  etc., 
the  following  results  are  obtained  : 

Fresh  clay  slate.  Vein  clay  slate.    Variegated  clay 

slate. 

Per  cent.  Per  cent.  Per  cent. 

Sericite,       .         .         .         .39.24  47.45  34.89 

Chlorite,      ....     16.54  4.37  

Quartz,        .         .         .         .35.30  34.40  63.24 

These  are  the  averages  of  the  calculations  of  all  the  analyses. 
The  character  of  the  alteration  is  thus  clearly  seen  to  consist  in 
a  chemical  change  of  the  chlorite  into  sericite,  with  simultane- 
ous subtraction  of  FeO  and  MgO.  The  quartz  is  practically 
constant. 

In  the  case  of  the  variegated  clay  slates,  the  change  appears 
to  be  of  a  different  kind.  A  comparison  of  the  third  column 
with  the  first  shows  that  the  following  reactions  have  taken 
place :  1.  The  chlorite  has  been  completely  destroyed ;  its 
bases  have  been  carried  away,  and  its  silica  has  probably  been 
added  to  the  free  quartz.  2.  The  percentage  of  sericite  has 
been  diminished  (more,  in  fact,  than  the  4  per  cent,  shown  by 
the  comparison  of  the  calculations,  since  we  must  consider  the 
amount  of  the  bases  carried  away).  3.  The  percentage  of  quartz 
has  been  increased  by  the  introduction  of  free  silica  besides 
that  obtained  from  the  alteration  of  the  sericite  and  the  chlo- 
rite. It  must  again  be  emphasized  that  this  process  points  to 
the  action  of  a  solvent,  probably  sulphuric  acid,  capable  of  car- 
rying away  considerable  amounts  of  alumina. 

The  Democrat  Vein,  Hailey,  Idaho. — The  Carboniferous  strata 
near  Wood  river,  Idaho,  contain  masses  of  intrusive  granite, 
or,  as  more  specifically  determined,  quartz-monzonite.*  This 
rock  is  cut  by  fissure-veins  containing  galena,  sphalerite  and 
tetrahedrite,  with  siderite  and  calcite  gangue ;  the  ore  being 
due,  partly,  to  filling  of  open  fissures,  partly  to  replacement. 
For  a  few  feet  on  each  side  of  the  vein,  the  granite  is  altered 
and  contains  some  pyrite,  galena  and  zinc-blende.  The  altered 
rock  is  of  greyish-green  color  and  its  texture  unmistakably  in- 
dicates its  derivation.  The  biotite  of.  the  granite  is  converted 

*  W.  Lindgren,  20^  Ann.  Eept.  U.  S.  Geol.  Surv.,  part  iii.,  pp.  206  and  212. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINfe. 


605 


to  large  foils  of  muscovite ;  the  feldspars  are  also  completely 
changed  to  radial  tufts  and  scaly  aggregates  of  sericite,  mixed 
with  calcite  grains.  The  quartz  grains  are  in  places  vigorously 
attacked  by  sericitization  and  carbonatization,  in  the  manner 
illustrated  in  Fig.  13.  The  apatite  is  completely  unaltered,  and 
the  titanite  is  converted  to  bunches  of  rutile  needles.  A  little 
chlorite  remains.  For  complete  analyses  and  calculations,  the 
reader  is  referred  to  the  report  cited.  The  altered  rock  con- 
sists of:  Quartz,  55.07;  sericite,  31.78;  chlorite,  7.21;  calcite, 
4.39;  siderite,  0.05 ;  rutile,  0.40;  apatite,  0.23;  pyrite,  0.19; 
pyrrhotite,  0.07;  zinc-blende,  0.14;  water  (hygroscopic),  0.37; 
total,  99.90  per  cent. 

From  the  determination  of  specific  gravity  it  is  concluded 
that  no  change  of  volume  has  taken  place,  but  the  granite  has 
altered  to  an  aggregate  of  denser  minerals ;  the  result  being  a 
rock  of  considerable  porosity.  On  this  basis,  namely,  the  com- 
parison of  equal  volumes,  the  following  changes,  expressed  in 
kilograms  per  cubic  meter,  have  taken  place  : 

TABLE  VII. — Gains  and  Losses  of  Country-Rock  of  the  Democrat 
Vein,  Idaho,  During  Alteration. 


GAIN. 

Loss. 

Per  Cubic 
Meter  of  Origi- 
nal Rock. 

Percentage  of, 
for  Each  Con- 
stituent. 

Per  Cubic 
Meter  of  Origi- 
nal Rock. 

Percentage  of, 
for  Each  Con- 
stituent. 

SiO2... 

Kilos. 

Per  cent. 

423 
1500 

1550 

nearly  all. 
nearly  all. 
all. 

all.' 

Kilos. 
49 
3 
99 
10 

"*6" 
1 
3 
18 
33 
80 
5 

"*i" 

Per  cent. 
2.7 
2.3 
24.7 
61.6 

"8.5 

100.0 
100.0 
56.2 
29.0 
93.0 
35.8 

25.6 

TiO2  

ALO«... 

FeO... 

FeO 

22 
3 

MnO 

CaO     ... 

SrO  

BaO  

MgO  

K2O  

Na2O 

H2O  below  105°  C 

H2O  above  105°  C  
P2O-... 

31 

c62° 

43 

4 
3 

s. 

Fe         

Co,  Ni  

Zn  , 

2 

108 

308 

606  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

The  result  shows  a  total  loss  of  substance  of  200  kilograms 
per  cubic  meter.  The  losses  extend  over  all  the  bases  and  the 
silica ;  baryta  and  strontia  being  completely  removed  without 
the  appearance  of  barite  in  the  vein.  The  gains  chiefly  con- 
sist in  water,  carbon  dioxide,  ferrous  oxide,  sulphur  and  zinc. 
Both  potash  and  soda  are  removed ;  the  former  only  partially, 
the  latter  almost  completely.  Calculated  without  regard  to 
porosity,  by  comparing  equal  weights,  the  result  is  reached 
that  the  rock  has  received  an  addition  of  substance ;  but  the 
manner  here  indicated  is  doubtless  the  correct  way  of  regard- 
ing the  process. 

14.  Zeolitic  Copper- Veins. 

The  copper-deposits  of  Michigan  are  in  part  fissure-veins  cut- 
ting across  the  beds  of  melaphyre  and  other  basic  igneous  rocks 
so  common  in  that  district.  It  is  true,  however,  that  the  ore- 
bodies  of  the  large  mines  are  not  to  be  considered  as  fissure- 
veins,  but  rather  as  beds  or  strata  along  which  copper  has  been 
deposited  by  a  process  of  replacement.  R.  Pumpelly*  investi- 
gated the  copper-deposits  of  Michigan  and  published  part  of  his 
results  in  1873.  Further  contributions  to  the  same  subject  are 
found  in  his  celebrated  paper  on  "  The  Metasomatic  Develop- 
ment of  the  Copper-Bearing  Rocks  of  Lake  Superior. "f  In 
these  investigations  the  theory  of  metasomatic  replacement  was 
applied  to  American  ore-deposits,  and  in  this  field  Prof.  Pum- 
pelly is  clearly  the  pioneer  in  this  country.  The  copper- 
bearing  veins  contain  a  number  of  minerals  not  ordinarily 
present  in  fissure-veins,  and  are,  therefore,  of  special  interest. 
Among  these  minerals  are  the  zeolites  :  laumontite,  apophyllite 
and  analcite.  There  are  also  present  as  gangue  minerals,  preh- 
nite,  datolite,  chlorite,  delessite,  calcite,  orthoclase  and  quartz. 
The  principal  ore-mineral  is,  of  course,  the  native  copper.  Of 
sulphides,  chalcocite  and  bornite  are  sometimes,  but  very  rarely, 
encountered. 

According  to  Pumpelly's  description,  the  veins  must  be  due 
in  part  to  filling ;  but  very  largely,  perhaps  predominantly,  the 
ore  results  from  metasomatic  replacement.  The  stages  of  this 
alteration  Prof.  Pumpelly  considers  to  have  been  :  1.  A  forma- 

*  Oeol  Surv.  of  Mich.,  vol.  i.,  part  ii. 

f  Proc.  Am.  Acad.  of  Arts  and  Sciences,  vol  xiii.,  1877-78,  p.  253. 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  607 

tion  of  chlorite  in  the  amygdaloid  rock;  2.  Individualization 
of  non-alkaline  silicates,  such  as  laumontite,  prehnite  and  epi- 
dote;  3.  Deposition  of  quartz ;  4.  Introduction  of  native  cop- 
per, accompanying  which  there  was  a  replacement  of  prehnite 
by  a  green  earth  or  delessite,  often  intimately  connected  with 
the  copper;  5.  Appearance  of  the  alkaline  silicates,  such  as 
apophyllite,  orthoclase  and  analcite. 

This  occurrence  of  secondary  orthoclase  or  adularia  is  of 
special  interest  in  view  of  the  fact  that  the  same  mineral  has 
lately  been  found  to  form  an  important  gangue-constituent  in 
certain  Tertiary  fissure-veins  in  volcanic  rocks  of  the  West. 
It  is  considered  that  the  alkaline  silicates  represent  the  final 
stage,  namely,  the  decomposition  of  the  labradorite  of  the 
original  rock,  while  the  chloritization  represented  the  first 
stage  of  alteration,  namely,  that  of  ferro-magnesian  silicates  to 
chlorite.  Prof.  Pumpelly  thinks  that  copper  was  originally 
present  as  sulphides  in  the  rocks,  and  that  the  changes,  consist- 
ing in  leaching  and  re-disposition  in  veins,  have  been  effected 
by  surface-waters  carrying  carbonic  acid  and  some  atmospheric 
oxygen.  The  copper  was  deposited  after  the  destruction  of 
the  ferro-magnesian  minerals,  and  before  the  deposition  of  the 
products  from  the  decomposition  of  the  feldspars.  From  the 
state  of  sulphide,  copper  was  converted  to  silicate,  carbonate 
and  sulphate.  These  salts  were  then  reduced  to  a  metallic 
state.  He  thinks  also  that  there  is  a  close  genetic  relation 
between  this  metallic  copper  and  the  ferric  condition  of  the 
iron  oxide  in  the  associated  silicates.  The  oxidation  of  the 
iron  was  caused  by  the  reduction  of  the  oxide  of  copper  at  the 
expense  of  the  oxygen  of  the  latter. 

Prof.  R.  D.  Irving,  in  his  report  on  "  The  Copper-Bearing 
Rocks  of  Lake  Superior,"*  confirms  in  general  the  conclusions 
of  Prof.  Pumpelly.  He  considers  the  veins  as  very  largely 
replacement-veins  not  sharply  defined  from  the  surrounding 
rocks,  but  simply  the  result  of  a  rock-alteration  entirely  analo- 
gous to  that  which  has  brought  about  the  deposition  of  copper 
and  its  associated  vein-stone  minerals  within  the  cupriferous 
amygdaloids.  They  are  alteration-zones,  which  traverse  instead 
of  follow  the  bedding.  The  replacement  of  wall-rock  by  cop- 

*  Monograph  V.,  U.  S.  Oeol  Surv.,  1883. 


608  METASOMATIC    PROCESSES    IN   FISSURE-VEINS. 

per  masses  is  a  common  occurrence ;  and  the  paragenesis  of 
the  vein-minerals  is  identical  with  that  of  the  copper-bearing 
amygdaloid  rocks. 

Especially  remarkable  is  the  series  of  replacements  which, 
as  shown  by  Pumpelly,  has  taken  place  in  these  veins.  Preh- 
nite  is  pseudomorphic  after  plagioclase ;  and  many  amygdaloids 
are  largely  prehnitized.  This  prehnite  is  again  replaced  by 
orthoclase  ;  and  finally,  the  latter  may  change  into  epidote  and 
quartz.  Sericite  is  absent. 

These  copper-bearing  veins  are  clearly  very  different  from 
the  majority  of  fissure-veins,  and  have  been  formed  under  very 
different  conditions — in  fact,  probably  not  by  thermal  waters. 
Of  other  classes,  the  orthoclase-albite-zeolite  veins  of  the  Alps 
are  most  closely  related ;  while  a  certain  slight  resemblance 
also  exists  to  the  propylitic  veins,  emphasized  by  the  chloritic 
alteration  and  the  presence  of  orthoclase. 

The  veins  of  Kongsberg,  Norway,  and  Andreasberg  in  the 
Hartz  mountains,  both  of  which  also  carry  zeolites,  are  not 
sufficiently  known  in  their  metasomatic  aspects  to  be  discussed 

here. 

Observed  Alteration  by  Ascending  Waters. 

Extremely  little  exact  work  has  been  done  in  this  most  im- 
portant line  of  investigation,  namely,  to  ascertain  actual  altera- 
tions by  waters  of  known  composition.  In  veins  we  usually 
have  only  the  altered  rock  as  a  known  quantity,  and  must  en- 
deavor to  draw  conclusions  from  this  as  to  the  character  of  the 
waters. 

Most  interesting  and  well  known  is  Prof.  Daubree's  discov- 
ery of  the  alteration  which  the  old  Roman  bricks  and  mortars 
have  suffered  at  the  place  where  the  mineral  springs  of  Plom- 
bieres  break  through  the  granite,  ascending  on  fissures  carry- 
ing fluorite  and  quartz.  The  waters  are  thermal,  having  a 
temperature  of  70°  C.,  and  maybe  characterized  as  weak  min- 
eral waters,  containing  sulphates  and  chlorides,  with  a  little 
hydrogen  sulphide ;  silicates  of  potash  and  soda  are  also 
present  in  them.  In  the  bricks  employed  by  the  Romans  as 
curbing  for  the  spring,  a  number  of  minerals  have  been  depos- 
ited. Chief  among  them  are  the  zeolites.  Chabazite,  meso- 
type,  and  apophyllite  are  the  principal  minerals  formed  in  the 
pores  and  spaces  of  dissolution  in  the  old  bricks.  Besides 


METASOMATIC   PROCESSES    IN   FISSURE-VEINS.  609 

these,  opal  and  chalcedony  have  been  deposited ;  and,  on  one 
piece  of  mortar,  fluorite,  scalenohedrons  of  calcite,  and  prisms 
of  aragonite  were  also  found.  This  is  extremely  interesting, 
as  the  fissures  on  which  the  spring  rises  contain  much  fluorite. 
The  apophyllite  also  was  found  to  contain  a  notable  percentage 
of  fluorine.  An  analysis  of  this  altered  brick  gave  the  follow- 
ing result:  Si02, 19.39  ;  A1203, 17.33;  Fe203,5.37;  CaO,  51.40  ; 
MgO,  0.75;  K20,  5.94;  Na20,  0.33;  total,  100.51  per  cent. 

In  this  analysis  the  most  remarkable  fact  is  the  strong  preva- 
lence of  potash  and  the  small  quantity  of  soda  present.  It  is 
scarcely  to  be  assumed  that  the  ordinary  bricks  of  that  locality 
contained  the  alkalies  in  this  proportion.  The  porous  bricks 
were  evidently  specially  adapted  for  the  formation  of  new 
minerals,  and  the  large  percentage  of  lime  in  the  mortar  also 
facilitated  the  process.  Daubree  mentions  that  pieces  of  gran- 
ite enclosed  in  the  same  mass  show  no  zeolitization,  and  refers 
at  the  same  time  to  the  fact  that  pyroxene  and  feldspar  show 
no  alteration  in  the  same  superheated  glass  tubes  in  which 
glass  is  completely  transformed  into  zeolites  and  into  silica. 
This  shows  in  a  striking  manner  the  dependence  of  the  altera- 
tion of  the  country-rock  upon  its  structure  and  composition. 

Mr.  W.  H.  Weed  has  recently*  found  a  mineral  vein  in 
process  of  formation  by  a  weak  thermal  water  at  Boulder, 
Montana.  The  vein-filling  consists  of  quartz,  calcite  and  some 
stilbite,  while  the  adjoining  granite  is  partly  altered  to  sericite 
and  kaolinite ;  these  two  minerals  attacking  all  of  the  primary 
constituents  (Fig.  19).  A  little  free  silica  is  also  mixed  with 
the  kaolinite.  In  some  specimens  the  kaolinite  and  sericite 
are  subordinate  and  the  feldspar  appears  partly  silicified. 

CONCLUSIONS. 

Some  of  the  following  conclusions,  drawn  from  the  data 
presented  in  this  paper,  may  seem  trite  repetitions  of  already 
known  facts;  but  it  is  perhaps  well  to  remember  that  our 
knowledge  of  the  genesis  of  mineral  deposits  is  not  built  on 
such  firm  foundations  that  it  does  not  need  fortification  of  its 
position  by  conclusions  from  all  possible  view-points. 

1.  Almost  all  fissure-veins  are  bordered  by  altered  zones  of 

*  Communicated  to  me  from  an  unpublished  paper. 


610  METASOMATIC    PROCESSES   IN   FISSURE-VEINS. 

varying  extent  and  intensity  of  alteration.  In  the  so-called 
"  replacement-veins  "  this  altered  and  replaced  rock  contains 
the  valuable  ore. 

2.  The  metasomatic  processes  in  different  classes  of  veins 
show  an  almost  kaleidoscopic  variety.     In  one  class  of  veins, 
quartz  may  be  converted  into  calcite,  while  in  a  different  class 
calcite  may  be  converted  into  quartz.     The  action  is  usually  in- 
tense, involving  a  great  change  in  the  chemical  composition. 

3.  The  hydration  connected  with  the  alteration  is  only  very 
moderate. 

4.  The  most  prominent  mineral  formed  by  the  metasomatic 
processes  is  a  potassium  mica  (muscovite,  sericite,  zinnwaldite 
and  many  other  related  species).    The  most  prominent  process  is 
the  progressive  elimination  of  soda  and  concentration  of  potash, 
closely  connected  with  the  formation  of  potassium  mica. 

5.  The  metasomatic  processes  in  fissure-veins  differ  distinctly 
in  most  cases  from  those  involved  in  ordinary  static,  dynamic 
and  contact  metamorphism,  and  the  two  classes  of  change  have 
not  generally  taken  place  under  the  influence  of  the  same  con- 
ditions and  agencies.     Greisen  is  only  found  near  cassiterite- 
veins.      Granite,  thoroughly  changed  to   sericite,  calcite  and 
pyrite,  is  never  found  as  a  result  of  any  other  metamorphism 
than  in  fissure-veins,  nor  are  fluoritized  or  sideritized  rocks  so 
found.     The  propylitic  and  biotitic  alteration;    the    chloritic 
and  zeolitic  alteration  of  Lake  Superior  copper- veins ;  and  the 
silicificatioii  in  limestone  and  other  rocks   form    exceptions, 
being  similar  to  certain  developments  of  dynamic,  static  and 
hydrochemic  metamorphism. 

6.  Ordinarily,  the  alteration  consists  in  the  total  or  partial 
loss  of  certain  constituents ;  the  gain  of  others ;  and  the  intro- 
duction of  new  compounds  and  elements,  usually  carbon  diox- 
ide and  sulphur.      The  net  total  of  the  change  per  unit  of 
weight  or  volume  may  be  a  gain  or  a  loss,  perhaps  more  often 
the  former.     If  sulphides  are  abundantly  introduced,  the  result 
will  usually  show  a  strong  gain  in  mass. 

7".  The  processes  observed  are  such  as  can  only  be  explained 
by  aqueous  agencies.  Possible  exceptions  are  the  forms  of 
alteration  connected  with  cassiterite,  apatite  and  tourmaline- 
veins,  in  which  pneumatolytic  conditions  may  have  partly 
obtained.  >;.: 


METASOMATIC    PROCESSES    IN    FISSURE-VEINS.  611 

8.  The  intensity  of  the  processes  observed  indicates  that  the 
aqueous  solutions  acted   under  moderately  high  temperature, 
pressure  and  concentration.    No  cold,  pure  surface-water  could 
produce  such  results  as  are  ordinarily  found. 

9.  From  the  fact  that  the  substances  introduced,  such   as 
sulphur,  carbon-dioxide,  fluorine,  boron  and  heavy  metals,  are 
only  known  to  be  contained  in  noteworthy  quantities  in  ther- 
mal waters  ascending  on  fissures,  it  is  concluded  that  these 
waters  were  the  agencies  usually  active  in  the  process  of  altera- 
tion. 

10.  Many  of  the  substances  found  in  the  filling  of  the  open 
spaces  along  the  fissure  may  be  lacking  in  the  altered  rock, 
showing  that  the  latter  forms  a  septum  not  penetrated  with 
equal  ease  by  all  constituents  of  the  solution.* 

11.  The  ascending  waters  are  chiefly  surface-waters,  which, 
after  a  circuitous  underground  route,  have  found  in  a  fissure 
an  easy  path  on  which  to  return.     During  their  long  downward 
passage  they  doubtless  dissolve  much  material  from  the  rocks 
which  they  penetrate ;  and  this  solution  was  facilitated  by  the 
gradually  increasing  heat  and  pressure  with  increasing  depth. 
During  the  ascending  period,  much  of  this  material  is  depos- 
ited.    The   metasomatic   action   on   the   wall-rock   results  in 
further  exchanges  of  constituents,  some  being  dissolved  and 
others  deposited. 

For  many  veins,  this  genetic  theory  may  be  fully  sufficient. 
But  for  many  others,  perhaps  for  the  majority  of  fissure-veins, 
something  seems  to  be  lacking  in  this  explanation.  The  differ- 
ence in  the  metasomatic  processes  in  veins  and  in  other  forms 
of  metamorphism  must  be  taken  into  consideration,  as  well  as 
the  abundance  of  certain  constituents,  such  as  carbon  dioxide 
and  hydrogen  sulphide,  in  mineral  waters.  The  presence  of 
these  constituents  has  not  been  satisfactorily  explained,  and 
cannot  be,  except  in  certain  cases,  on  the  theory  of  solutions 
derived  from  the  solid  country-rock. 

I  believe  that  the  majority  of  fissure-veins  are  genetically 
connected  with  bodies  of  intrusive  rocks,  even  when  the  actual 
deposits  are  contained  in  the  overlying  surface  lavas.  It  is 
well  known  that  the  intrusive  rocks,  such  as  granite,  diorite 

*  The  existence  of  such  osmotic  conditions  was  first  suggested  by  G.  F.  Becker 
(U.  S.  Qeol.  Surv.,  Min.  Res.,  1892,  " Quicksilver  Ore-Deposits, "  p.  159). 

39 


612  METASOMATIC    PROCESSES    IN    FISSURE-VEINS. 

and  gabbro,  may  contain  at  the  time  of  their  intrusion  water, 
carbon  dioxide,  fluorine,  boron  and  sulphur.  Under  decreas- 
ing pressure,  these  substances  have  a  tendency  to  leave  the 
cooling  magma;  and  as  many  of  them  form,  with  the  heavy 
metals  also  contained  in  the  magma,  volatile  compounds 
with  a  low  critical  temperature,  these  heavy  metals  may  be 
carried  away  from  the  magma  along  with  the  "  mineralizing 
agents "  mentioned  above.  This  is  the  well-known  theory 
which  was  originated  by  Elie  de  Beaumont  and  Daubree,  and 
developed  by  other  French  investigators ;  but  until  recently  it 
has  hardly  received  the  attention  which  it  deserves.  The 
results  of  these  emanations  is  shown  in  the  contact  metamor- 
phism  and  in  the  mineral  deposits  often  appearing  near  the 
boundaries  of  intrusive  bodies.  Where  fissures  traverse  the 
cooling  magmas,  and  the  rocks  surrounding  them,  it  is  natural 
that  these  mineralizing  agents  carrying  their  load  of  heavy 
metals  should  ascend,  at  first  under  pneumatolytic  conditions, 
above  the  critical  temperature.  Reaching  the  zone  of  circu- 
lating atmospheric  waters,  it  is  natural  that  they  should  mix 
with  these,  which  probably  greatly  predominated  in  quantity. 
To  this  combination  of  agencies,  found  in  the  ascending 
waters  of  such  regions  of  igneous  intrusion,  the  formation  of 
most  metalliferous  veins  is  probably  due.  This  dependence  of 
veins  on  intrusive  bodies  is  most  clearly  perceived  in  certain 
cassiterite-,  apatitp-  and  tourmaline-veins;  but  from  these  all 
sorts  of  transitions  may  be  found,  to  veins  of  more  ordinary 
character. 

I  am  by  no  means  prepared  to  deny  that  some  classes  of 
veins  may  be  due  to  circulating  surface-waters  alone ;  but  I  do 
not  believe  that  the  dissolving  power  of  the  latter  is  sufficient 
to  account  for  ,all  classes,  or  even  for  the  majority,  of  fissure- 
veins. 


DISCUSSIONS. 

(SECRETARY'S  NOTE.)  The  following  discussion  of  the  papers  of  Van  Hise, 
Emmons,  Lindgren  and  Weed,  read  at  the  Washington  meeting,  February,  1900, 
and  printed  on  pp.  282  to  498  of  this  volume,  comprises  communications  to  the 
•Secretary,  received  at  various  times  before  the  Richmond  meeting,  February, 
1901,  and,  for  the  most  part,  presented  at  that  meeting.  These  communications 
are  introduced  at  this  point  in  the  present  volume,  in  order  that  they  may  precede 
the  papers  of  Vogt,  Kemp,  Lindgren,  Bickard,  etc.,  presented  at  Richmond,  and 
therefore  not  forming  part  of  the  material  considered  in  them.  Since  many  of 
the  contributors  have  mentioned  in  one  communication  several  of  the  papers  re- 
ferred to,  no  attempt  is  here  made  to  divide  their  remarks  and  distribute  the 
fragments  under  separate  headings.  In  each  contribution,  however,  the  several 
topics  are  indicated  by  sub- titles. 

R  BECK,*  Freiberg,  Saxony :  Prof.  Van  Rise's  Paper. — The 
paper  of  Prof.  Van  Hise  (p.  282)  represents  a  great  step  of 
scientific  progress,  in  that  the  circulation  of  underground 
waters  has  never  before  been  presented  with  such  clearness,  in 
the  light  of  modern  chemical  and  physical  knowledge.  The 
theories  of  the  formation  of  ore-deposits  which  follow  the 
author's  general  survey  of  the  currents  and  solvent  power  of 
atmospheric  waters  in  the  earth's  crust  do  not,  indeed,  seem 
to  be  novel,  being  essentially  an  amplification  of  Le  Conte's 
views;  but  the  proofs  adduced  in  their  support  are  in  many 
particulars  so  original  that  no  one  can  read  without  profit  this 
portion  of  the  paper. 

Entirely  new  (though  largely  in  agreement  with  the  papers 
of  Emmons  and  Weed,  presented  at  the  same  meeting  of  the 
Institute)  are  the  sections  dealing  with  the  formation  of  the 
rich  sulphides  of  the  precious  metals,  and  especially  the  re- 
generation of  normal  sulphides,  such  as  galena,  etc.,  in  vein- 
zones  immediately  beneath  the  ground-water  level. 

Nevertheless,  it  appears  to  me  that  Prof.  Van  Hise,  in  the 
course  of  his  most  instructive  exposition  of  unquestionable, 
yet  still  locally  limited,  phenomena,  has  been  too  much  biased 
in  favor  of  the  "  descensionists."  This  is  indicated  by  the 
small  importance  which  he  attaches  to  the  intimate  genetic  re- 
lation between  epigenetic  deposits  and  the  plutonic  hearths  of 
the  earth's  interior. 


*  Professor,  Royal  Saxon  Mining  Academy.    Translated  by  the  Secretary,  and 
translation  approved  by  the  author. 

(613) 


614  THE    GENESIS    OF    ORE-DEPOSITS. 

In  my  treatise,  just  published,*  I  have  proved  from  many  in- 
stances that  the  formation  of  ore-veins  is  frequently  a  direct 
consequence  of  the  plutonic  intrusion,  particularly  of  acid 
magmas.  Prof.  Van  Hise  recognizes  such  a  relation  only  to 
this  extent,  that  atmospheric  waters,  in  their  downward  course, 
may  have  happened  to  reach  eruptive  masses,  perhaps  long 
since  solidified,  though,  in  common  with  the  enclosing  rocks, 
still  warm,  and  may  have  extracted  the  disseminated  mineral 
compounds  from  these  old  magmas.  But  we  still  hold  to  the 
conception  of  an  immediate  relation  in  time  also.  We  hold  as 
a  primary  principle  that  the  gases  and  vapors  contained  in  the 
fused  magmas,  and  escaping  as  these  cooled,  must  have  played, 
as  carriers  of  metallic  compounds  upwards  from  the  region  of 
the  plutonic  hearth,  a  very  active  part.  Especially  does  the 
study  of  contact-metamorphism  (e.g.,  at  Kristiania,  Norway,  in 
the  Banat,  and  at  Berggiesshfibel  in  Saxony)  strengthen  us  in 
this  conviction. 

As  concerns  the  cassiterite-veins,  this  view  has  many  ad- 
herents. The  direct  connection  between  granite  intrusions  and 
the  formation  of  veins  carrying  tin-ore,  I  have  lately  been  able 
to  establish  still  more  firmly  by  showing  that  at  Zinnwald,  in 
Saxony,  small  cassiterite-veins  in  the  periphery  of  the  granite 
mass  of  that  district  are  cut  by  veins  of  a  fine-grained  "  vein- 
granite."  The  deposition  of  the  tin-ore  must  therefore  have 
been  still  in  progress  at  the  time  of  additional  intrusions  of 
granite  from  below. 

But  there  is  by  no  means  in  the  Erzgebirge  a  sharp  separation 
between  the  veins  of  cassiterite  and  those  of  silver-lead-ores. 
The  latter  sometimes  contain  constituents  characteristic  of  the 
tin-ore  group ;  and  they  are  likewise  connected  with  the  in- 
trusive plutonic  masses  of  the  Erzgebirge. 

The  latest  work  of  American  observers  upon  gold-veins,  es- 
pecially that  of  Spurr  and  of  Hussak  (Brazil),  has  shown  that, 
for  many  gold-quartz-veins  also,  there  must  exist  a  very  in- 
timate genetic  and  chronological  connection  with  deep  plutonic 
intrusions.  Thus,  the  nature  of  many  gold-quartz-veins  is 
closely  allied  to  that  of  the  pegmatites — those  peculiarly-modi- 
fied derivatives  from  deep  granitic  hearths.  In  this  depart- 
ment also,  the  purely  hydro-chemical  theory  of  Prof.  Yan 

*  Lehre  von  den  Erzlagerstatten,  Leipzig,  1901. 


THE    GENESIS    OF    ORE-DEPOSITS.  615 

Hise  appears  to  be  inadequate.  The  facts  suggest  too  strongly 
an  active  participation  of  subterraneous  plutonic  masses,  par- 
ticularly through  the  expulsion  of  gases,  which  may  have  be- 
come mixed  with  ascending  waters. 

The  Papers  of  Emmons  and  Weed. — The  meritorious  work 
of  Messrs.  Emmous  and  Weed  (pp.  433  and  473),  opening  as  it 
does  a  wide  field  hitherto  unknown,  or,  at  least,  entirely  ne- 
glected, will  certainly  call  forth  a  long  series  of  confirma- 
tory observations.  I  have  not  yet  found  time  to  ascertain 
by  closer  study  to  what  extent  our  Freiberg  district  shows  sec- 
ondary sulphide-enrichment  by  descending  solutions.  To  a 
limited  degree  it  is  certainly  present,  e.g.  in  the  not  infre- 
quent thin,  sometimes  dendritic,  coating  of  silver-glance  or 
native  silver  on  cross-fissures  in  older  vein-fillings,  or  the  druses 
of  beautifully  crystallized  rich  silver-ores  in  geodes.  The 
crystals  of  stephanite  in  the  interstices  of  a  breccia  in  the  Him- 
melsfiirst  mine,  for  instance,  may  fairly  be  considered  as  later 
deposits  from  descending  waters.  But  it  is  very  doubtful,  to 
say  the  least,  whether  our  great  bonanzas  belong  in  this  cate- 
gory. In  our  case,  the  question  is  exceedingly  complicated, 
because  the  ground-water  level  has  probably  been  more  than 
once  displaced,  upward  or  downward. 

Our  veins,  admittedly  formed,  for  the  most  part,  before  the 
Cretaceous  period,  may  have  stood  long  already,  at  the  time  of 
the  great  Cenomanian  disturbance  and  erosion,  with  their  upper 
zones  above  ground-water  level.  For  only  a  couple  of  miles 
from  Freiberg,  and  about  at  the  same  altitude,  Cretaceous  strata 
are  now  found  lying  upon  the  gneiss  (in  that  locality  deeply 
decomposed)  which,  near  the  town  of  Freiberg,  encloses  the 
veins.  Thick  masses  of  Cenomanian  Cretaceous  sandstones  were 
unquestionably  denuded  again,  in  the  Freiberg  mining  district 
itself,  during  the  Tertiary.  The  vein-zones  which,  during  the 
Cretaceous,  were  crowded  deep  below  the  ground-water  level, 
must  have  been  elevated  again,  therefore,  in  Tertiary  times, 
above  that  level. 

Exact  observations  and  assured  conclusions  are  moreover 
made  difficult,  practically,  by  the  circumstance  that,  at  the 
present  time,  only  those  vein-zones  are  being  mined  which  lie 
far  below  the  natural  ground-water  level. 


616  THE    GENESIS    OF    ORE-DEPOSITS. 

Students  at  a  distance  might,  perhaps,  infer  from  descriptions 
of  this  district  that  the  rich  sulphide-ore-bodies  found  in  our 
"  barytic  lead-ore  formation,"  at  its  crossings  with  the  veins  of 
the  "  pyrite-blende-lead-ore  formation,"  belong  in  the  category 
of  enrichments  so  well  described  by  Emmons  and  Weed.  The 
mineralogical  composition  of  these  bonanzas,  with  its  abun- 
dance of  argentite,  proustite,  pyrargyrite,  acanthite,  stephanite, 
polybasite,  and  native  silver,  is  indeed  similar  to  that  of  the 
bonanzas  in  Montana  silver- veins.  Yet  the  veins  of  our  barytic 
lead-ore  system  do  not  at  all  exhibit  the  characteristics  of 
"  descensive  "  formations — their  abundance  in  fluorite  alone 
contradicts  such  a  view.  The  rich  ore-bodies  at  the  intersec- 
tions referred  to  must  be  rather  explained  as  simply  due  to 
chemical  reaction  between  the  masses  of  normal  sulphides 
(pyrite,  galenite,  chalcopyrite,  arsenopyrite  and  sphalerite)  in 
the  older  veins,  and  the  ascending  solutions  in  the  fissures  of 
the  later  barytic  lead-ore  system.  Emmons  himself  (p.  472) 
concedes  the  probability  of  such  reactions  in  many  cases. 

However  great  may  be  our  pleasure  and  praise  in  connection 
with  these  latest  victories  of  science,  we  must  nevertheless  be 
warned  not  to  attach  to  them  too  universal  a  significance. 

Mr.  Lindgren's  Paper. — With  regard  to  Mr.  Lindgren's 
paper,  I  will  frankly  say  that  since  the  death  of  Stelzner 
nothing  has  appeared  in  which  the  methods  of  microscopic- 
chemical  research  have  been  applied  with  such  splendid  suc- 
cess to  the  subject  of  ore-deposits.  I  agree  (with  insignificant 
exceptions)  so  thoroughly  with  the  conclusions  which  the 
author  has  drawn  from  his  brilliant  investigations,  that  it 
would  be  useless  for  me  to  offer  at  this  time  any  detailed 
criticisms.  I  can  only  express  my  delight  that  Stelzner's 
method  has  found  in  Mr.  Lindgren  an  adequate  American 
representative,  master  at  the  same  time  of  the  European 
literature  of  the  subject. 

L.  DE  LAUNAY,*  Paris,  France  :  Papers  of  Emmons  and  Weed. — 
The  ideas  set  forth  by  Mr.  Emmons  (p.  433)  on  the  secondary  en- 
richment of  ore-deposits,  and  by  Mr.  Walter  Harvey  Weed  (p.  473) 

*  Prof. ,  iZcole  Superieure  des  Mines.  Translated  by  the  Secretary,  and  transla- 
tion approved  by  the  author. 


THE    GENESIS    OF    ORE-DEPOSITS.  617 

on  the  enrichment  of  mineral  veins,  agree  almost  entirely  with 
my  own  ;  and  I  can  only  congratulate  myself  upon  finding  their 
observations  so  completely  in  accord  with  those  I  have  had 
occasion  to  make,  and  thank  them  for  the  very  kind  way  in 
which  they  have  been  good  enough  to  cite  rny  writings.  I 
have  recently  twice  reiterated  my  opinion  on  these  subjects : 
first,  in  an  article  in  the  Revue  Generate  des  Sciences*  on  "  The 
Variations  of  Metalliferous  Veins  in  Depth;"  secondly,  in  a 
little  text-book  on  practical  geologyf  (in  the  chapters  on  super- 
ficial formations  and  the  alterations  of  outcrops,  pp.  50  to  72). 
t  have,  therefore,  little  to  add.  As  I  have  said  in  these  essays, 
I  attach  more  and  more  importance  to  the  phenomena  of  sec- 
ondary alteration,  which  have  produced  a  number  of  important 
modifications  (whether  enrichments  or  impoverishments)  in 
those  portions  of  metalliferous  deposits  accessible  to  exploi- 
tation ;  and  I  fully  adopt  the  conclusion  of  Mr.  Weed  as  to 
the  necessity  of  taking  very  careful  account  of  these  phe- 
nomena in  practical  and  industrial  estimates.  I  think,  like- 
wise, that  in  these  secondary  and  comparatively  recent  reac- 
tions should  be  sought  the  interpretation  of  many  of  the  phe- 
nomena of  substitution,  lateral  alteration,  or  metasomatism,  in 
the  form  in  which  they  are  now  observed ;  while  I  continue  to 
admit,  with  the  school  of  Elie  de  Beaumont  and  Daubree  (to 
which  Mr.  Waldemar  Lindgren  brings  valuable  support),  the 
primary  influence  of  volatile  mineralizers.  These  must  have 
prepared  the  way  by  introducing  into  the  enclosing  rocks,  or 
simply  by  depositing  in  the  vein-fissures,  elements  such  as  sul- 
phides, fluorides,  chlorides,  etc.,  which  subsequently,  dissolved 
anew  by  the  circulation  of  superficial  waters,  have  rendered  to 
the  latter  essential  aid  in  the  processes  of  alteration.  In  this 
manner  have  been  produced  the  large  altered  zones  which  are 
seen,  for  example,  around  pyritic  masses  in  the  south  of  Spain. 
This  point  I  have  fully  elaborated  in  my  "  Contribution  to  the 
Study  of  Metalliferous  Deposits."! 

In  order  to  formulate  the  study  of  the  phenomena  in  ques- 
tion, I  have  been  led  to  distinguish  in  a  very  general  way,  in 
the  alterations  of  terranes  and  of  deposits,  three  zones  (from 

*  For  1900  ;  p.  568. 

t  Geologie  Pratique.     Published  by  Armand  Colin,  Paris,  1900. 

t  A  book  of  116  pp.,  Paris,  1877. 


618  THE    GENESIS    OF    ORE-DEPOSITS. 

the  surface  downward)  which  correspond  rather  to  those  of  Mr. 
Weed*  than  to  those  of  Mr.  Emmons, f  the  two  first  zones  of 
Mr.  Emmons  (the  reality  of  which  I  am  far  from  denying) 
having  been  comprised  in  the  first  of  mine ;  and  I  have  thus 
defined  them  :J 

1.  First  superficial  zone  of  oxidation,   subject,  in  its  upper 
part,  to  physical  disintegration :  a  zone  characterized  by  the 
peroxidation  of  iron,  and,  in  the  case  of  metalliferous  deposits, 
by  the  presence  of  native  metals,  oxides,  carbonates  or  chlorides 
(Mr.  Weed's  "  zone  of  weathering  "). 

2.  The  far  more  important  zone  of  cementation,  of  de-calcifi- 
cation, and,  more  generally,  of  complex  chemical  reactions  (such 
as  the  formation  of  secondary  sulphides),  liable  to  show  at  its 
base  an  increase  of  certain  substances,  which  have  been  dis- 
solved in  the  upper  part  and  carried  away  by  the  descending 
waters  (the  "  zone  of  enrichment "). 

3.  The  zone  of  unaltered  equilibrium  (unchanged  sulphides), 
below  the  hydrostatic  level  (the  "  zone  of  primary  sulphides  "). 

With  regard  to  the  process  of  this  alteration,  I  believe  with 
Mr.  Emmons  that  we  ought  not  to  attribute  too  absolute  a 
value  to  what  is  called  the  hydrostatic  level  ("  ground-water 
level "),  and  I  have  insisted  at  different  times  in  my  "  Geologie 
pratique  "  (pp.  52,  152,  etc.)  on  the  necessary  irregularities  of 
this  so-called  "  level,"  due  to  the  variable  structure  of  the  ter- 
rane,  and  leaving,  for  instance,  beneath  a  former  hydrostatic 
surface,  a  zone  in  which  the  circulation  of  surface-waters  rich 
in  oxygen  and  carbonic  acid  could  still  take  place. 

Moreover,  it  must  be  noted  that,  even  in  the  deep  zone,  the 
waters  could  not  be  absolutely  still  or  incapable  of  exercising 
oxidizing  chemical  reactions,  especially  if  there  be  great  fissures 
or  faults,  permitting  the  introduction  and  rapid  circulation  of 
waters  from  the  surface,  such  as  appear  to  exist  as  correlatives, 
opposed  to  the  ascent  of  thermal  waters, §  and  as  Mr.  Weed 

*  "  Enrichment  of  Mineral  Veins  by  Later  Metallic  Sulphides,"  Bull  Geol  Soc. 
of  Am.,  vol.  xi.,  p.  181  (1900)  ;  "  Enrichment  of  Gold-  and  Silver- Veins,"  Trans., 
xxx.,  424  ;  this  vol.,  pp.  473-497. 

f  "Secondary  Enrichment  of  Ore-Deposits,"  Trans.,  xxx.,  177;  this  vol., 
pp.  433-472. 

J  Geologie  pratique,  p.  54  ;  Revue  generate  des  Sciences,  1900,  p.  568. 

\  Traite  des  Sources  thermo-minerales  (Baudry,  Paris,  1899)  ;  chapters  on  the 
origin  and  outflow  of  thermal  springs,  in  which  I  have  called  attention  to  the 


THE    GENESIS    OF    ORE-DEPOSITS.  619 

has  well  pictured  in  his  Fig.  1.*  This  may  explain  the  ab- 
normal occurrence  of  certain  alterations  and  secondary  enrich- 
ments more  deeply  situated  than  might  have  been  at  first  ex- 
pected. Here  is  a  very  interesting  fact  which  Mr.  Weed 
deserves  the  credit  of  bringing  to  light. 

Perhaps  also,  besides  the  descending  waters,  the  ascending 
waters,  heated  by  their  deep  circulation,  or  even  by  contact 
with  eruptive  phenomena,  have  in  certain  cases  played  a  part 
which  their  high  temperature  may  have  augmented,  although 
we  may  suppose  them  to  have  been  robbed  of  oxidizing  re- 
agents by  their  subterranean  circulation.  We  know,  indeed, 
that  Daubree  observed  at  Plombieres,  Bourbonne,  etc.,  evident 
reactions  of  this  kind,  produced  upon  metals  by  prolonged  con- 
tact with  thermal  waters  of  extremely  low  mineralization ;  and 
certain  minerals,  especially,  which  may  be  considered  as  sec- 
ondary in  copper-deposits,  are  produced  under  these  condi- 
tions : — secondary  sulphides  such  as  those  studied  by  Mr. 
Weed,  who  has  elsewhere  mentioned  the  possibility  of  this  in- 
tervention of  hot  volcanic  waters. 

Furthermore,  as  I  have  long  since  remarked,  when  we  are 
confronted  with  secondary  reactions,  the  persistence  of  which 
in  depth  is  surprising,  and  appears  to  contradict  existing  theo- 
ries, there  is  reason  to  inquire  whether  the  surface  of  the  earth 
was  not,  by  reason  of  remote  tectonic  accidents,  very  different 
at  the  time  when  these  reactions  took  place  from  what  it  is  to- 
day. I  am  very  happy  to  see  that  in  their  admirable  study  of 
the  copper-mines  of  Butte,  Messrs.  Emmons  and  Weed  have 
been  led  not  only  to  adopt  a  similar  hypothesis,  but  to  give  it 
a  local  geological  confirmation. 

Finally,  I  beg  again  to  mention  an  idea  which  I  have  never 
had  occasion  to  state  heretofore  except  incidentally,  but  which 
seems  to  me  to  deserve  more  thorough  study.  Namely,  in  re- 
gions of  complex  fractures,  with  numerous  systems  of  inter- 
secting veins,  such  as  those  studied  so  minutely  in  Saxony, 


fact  that,  to  constitute  a  thermal  spring,  there  must  «xist,  below  the  hydrostatic- 
level,  an  active  circulation  which  I  have  compared  to  that  which  might  be  pro- 
duced in  a  pipe-elbow,  plunged  in  a  basin  of  water  (op.  tit.,  pp.  23  to  31).  The 
moving  waters  thus  rapidly  brought  by  accident  into  contact  with  the  lower  por- 
tion of  a  deposit  might  exercise  upon  it  an  unforeseen  metamorphosis. 
*  Trans.,  xxx.,  428  (p.  477  of  this  volume). 


620  THE    GENESIS    OF    ORE-DEPOSITS. 

Bohemia,  etc.,  there  is  doubtless  reason  to  attribute  a  very  im- 
portant role  to  secondary  phenomena  of  enrichment,  as  explain- 
ing the  variations  in  successive  fillings,  which  have  usually 
been  interpreted  as  primary  phenomena,  and  the  cause  of 
which  has  been  sought  in  a  series  of  internal  movements  more 
or  less  independent,  separated  by  long  intervals  of  time.  Per- 
haps, for  example,  the  occurrence  of  a  late  deposit,  of  highly 
argentiferous  mineral,  often  accompanied  with  calcite  and  co- 
balt, such  as  has  been  noted  at  Freiberg,  Przibram,  Wittichen, 
etc.,  is  only  the  result  of  a  simple  secondary  concentration. 
The  same  may  be  true  of  the  cobaltiferous  fillings  with  calcite 
and  barite,  which  have  been  observed  in  sundry  faults  travers- 
ing the  cupriferous  schists  of  Mansfeld ;  and  I  believe  that,  in 
a  general  way,  it  is  the  cause  of  many  enrichments  noticed  at 
the  intersections  of  veins,  at  the  junctions  of  cross-courses,  etc,, 
such  as  those  described  by  Smith  at  Broken  Hill  and  by  Spurr 
in  the  Aspen  district,  which,  judging  from  the  published  de- 
scriptions, Mr.  Weed  appears  to  me  to  have  interpreted  very 
justly. 

ARTHUR  L.  COLLINS,  Telluride,  Colo. :  Papers  of  Emmons 
and  Weed. — Mining  engineers  owe  a  great  deal  to  the  suggestive 
papers  of  Messrs.  Ernmons  and  Weed  (pp.  433  and  473),  which 
throw  much  light  on  numberless  facts  in  connection  with  ore- 
deposits,  especially  those  of  copper-  and  silver-ores. 

In  recent  papers  on  this  subject,  no  reference  has  been  made 
to  the  remarkable  copper-veins  of  Cornwall,  which,  only  60 
years  ago,  furnished  the  major  part  of  the  world's  copper- 
supply,  but  already  seem  to  be  almost  forgotten.  These  de- 
posits were  described  by  a  host  of  capable  observers,  includ- 
ing such  men  as  Delabeche,  Henwood  and  Smythe ;  and  the 
separate  zones  of  weathering,  enrichment  and  unaltered  ore 
which  they  exhibited  were  so  strongly  marked  and  so  commer- 
cially important  that  one  wonders  that  the  relations  of  these 
zones  were  not  recognized  at  the  time. 

The  zone  of  weathering  ("  gossan  ")  was  often  of  great  ex- 
tent, reaching  not  only  below  present  water-level,  but  far  below 
the  level  of  the  neighboring  sea.  Thus,  at  Fowey  Consols,  the 
gossan  extended  100  fathoms  below  the  adit-level ;  and  at  Dol- 
coath  "  some  of  the  earthy  brown  are  was  found  as  far  down 


THE    GENESIS    OF    ORE-DEPOSITS.  621 

as  the  197-fathom  level."*  These  gossans  generally  showed 
traces  of  copper ;  and  it  was  recognized  that  they  proved  the 
former  existence  of  sulphide-ores,  from  which  they  had  been 
formed. 

Immediately  below  came  the  great  ore-bodies,  such  as  that 
at  Clifford  Amalgamated,  "  16  or  18  ft.  wide,  of  cindery  copper 
pyrites  from  wall  to  wall;"  or  the  "  30  or  40'  ft.  of  dredgy  cop- 
per ore  in  the  best  parts  of  Devon  Consols. "f 

These  gradually  gave  place  to  poorer  ores,  until,  one  after 
another,  the  mines  were  abandoned.  Some  16  years  ago,  when 
one  of  these  old-time  Cornish  bonanzas,  the  Tresavean  mine, 
was  reopened,  the  hard  quartz  ore,  sparingly  sprinkled  with 
pyrite,  mispickel  arid  chalcopyrite,  which  was  encountered, 
seemed  to  justify  fully  its  former  abandonment.  The  recog- 
nition of  the  essentially  superficial  origin  of  rich  copper  sul- 
phide ore-bodies  of  this  type  will  be  discouraging  in  many 
cases.  But  it  only  confirms  an  opinion  long  held,  on  other 
grounds,  by  mining  engineers. 

It  is  noteworthy  that  the  reaction  mainly  relied  upon  for  the 
removal  of  copper  from  the  zone  of  weathering,  namely,  the 
decomposition  of  copper  sulphides  by  ferric  sulphate,  is  (or 
was,  many  years  ago,  when  I  was  familiar  with  the  district) 
employed  at  Rio  Tinto  on  a  very  large  scale  in  the  commercial 
treatment  of  copper-ore.  The  liquors  from  the  lixiviation  of 
heap-roasted  ore  were  run  over  "  raw  "  fine  ore — originally  (as 
I  recollect)  to  lessen  the  consumption  of  iron  in  the  precipitat- 
ing-tanks,  and  to  secure  a  cleaner  precipitate.  But  this  was 
found  to  be  also  an  efficient  method  of  extracting  part  of  the 
copper-contents  of  raw  pyrites.  And  great  heaps  of  mixed 
"  raw  fines,"  and  lixiviated  roasted  ore,  aggregating  millions  of 
tons,  gradually  giving  up  their  copper  in  solution,  largely  by 
means  of  this  reaction,  became  a  feature  of  the  Rio  Tinto  land- 
scape. 

The  supposed  reaction  for  the  re-precipitation  of  copper  in 
secondary  copper-ores,  from  cupric  sulphate  solutions  by  pyrites, 
can  hardly  take  place  under  these  conditions — it  would  upset 
the  commercial  process. 

The  evidence  of  secondary  enrichment  in  gold-  and  silver- 

*  T.  H.  Collins,  Journal  Royal  Inst.  of  Cornwall,  No.  38. 

f  Sir  "W.  Smythe,  Trans.  Royal  Geol.  Soc.  Cornwall,  vol.  xi.,  part  iv. 


622  THE    GENESIS    OF    ORE-DEPOSITS. 

veins  is  less  striking  than  in  copper-deposits.  As  to  gold  in 
particular,  we  are  accustomed  to  look  for  far  higher  values  in 
the  oxidized  surface-ores  than  in  the  sulphides  immediately  be- 
neath. This  may  be  due  as  much  to  the  ease  with  which  gold 
is  precipitated  from  its  solutions  as  to  its  original  insolubility; 
for  the  native  gold  in  oxidized  ores  often  has  every  appearance 
of  secondary  deposition. 

As  to  the  Smuggler-Union  workings  (of  which  I  am  at 
present  in  charge),  a  personal  examination  might  give  Mr. 
Emmoris  reason  to  doubt  the  suggestion  that  the  richer  silver- 
minerals  have  been  re-concentrated  into  a  more  recent  foot-wall 
streak.  Nor  does  any  such  streak  remain  unaffected  by  the 
faulting  at  the  Pandora  crossing,  so  far  as  our  workings  show. 
The  great  changes  in  the  Smuggler-Union  vein  with  depth 
seem  rather  to  coincide  with  the  changing  strata  through 
which  it  passes. 

More  striking  cases  might,  I  think,  be  found  in  the  Silver 
Plume  district  of  Clear  Creek  county,  Colo.,  where  the  rich 
silver-minerals  of  the  upper  parts  of  the  veins  have  given  place 
to  low-grade  galena  and  ferruginous  blende  in  depth,  without 
any  corresponding  change  in  the  enclosing  rocks  or  gangue- 
minerals. 

H.  FOSTER  BAIN,*  Des  Moines,  Iowa  :  Paper  of  Van  Hise. — 
The  zinc-  and  lead-deposits  of  the  Mississippi  valley,  which  it 
has  been  my  fortune  to  study,  give  particularly  good  exam- 
ples of  many  of  the  principles  of  ore-deposition  formulated  by 
Prof.  Van  Hise.  Perhaps  there  is  nowhere  clearer  evidence 
supporting  his  fundamental  tenet,  that  ore-bodies  are  to  be  re- 
garded as  a  result,  and  as  merely  one  of  the  phases,  of  the 
work  of  underground  waters.  The  facts  regarding  the  mines 
of  the  upper  Mississippi  valley  have  been  given  in  some  detail 
for  Wisconsin  by  Prof.  Chamberlinf  and,  more  recently,  for  the 
mines  west  of  the  Mississippi  by  the  Iowa  Geological  Survey. % 
Fortunately,  also,  the  processes  of  underground  water-circula- 
tion have  been  studied  in  some  detail  in  connection  with  the 


*  Published  by  permission  of  the  Director  of  the  U.  S.  Geological  Survey. 

f  Geology  of  Wisconsin,  vol.  iv.,  pp.  367-571. 

J  Leonard,  A.  G..  vol.  vi..  pp.  9-66.     Calvin  and  Bain,  vol.  x.,  pp.  480-597. 


THE    GENESIS    OF    ORE-DEPOSITS.  623 

investigation  of  artesian  waters  throughout  the  region.*  In 
Missouri  and  Arkansas  the  mines  and  ore-bodies  have  been 
much  studied;f  but  the  general  problems  of  the  circulation  of 
underground  waters  have  been  neglected.  During  the  season 
just  closed  the  writer  has  been  engaged  in  a  re-study  for  the 
United  States  Geological  Survey  of  the  zinc-  and  lead-deposits 
of  the  Ozark  region,  with  special  reference  to  those  of  the 
Joplin  area ;  and  his  full  report  is  now  in  preparation.  It  has 
been  interesting  to  note  how  fully  the  statement  that  the  ore- 
bodies  result  from  the  general  action  of  underground  waters  is 
here  substantiated.  Treated  merely  as  parts  of  a  problem  of 
water-circulation,  many  of  the  difficulties  regarding  the  ore- 
deposits  vanish. 

In  brief,  the  Joplin  area  is  one  in  which  flowing  wells  would 
occur,  if  it  were  not  for  the  numerous  deep  fractures  which, 
permitting  the  free  outflow  of  springs,  has  had  the  same  effect, 
in  causing  loss  of  head,  as  the  placing  of  wells  too  close  to- 
gether. The  gathering-ground  is  the  central  plateau  of  the 
Ozarks ;  the  overlying  impervious  layer  is  the  Eureka-Kinder- 
hook  shale,  which  divides  the  Carboniferous  from  the  Siluro- 
Cambrian.  The  aquifers  are  the  porous  dolomitic  limestones 
and  interbanded  sandstones  of  the  Siluro-Cambrian.  At  an 
earlier  stage  much  of  the  water  was  transmitted  down  the  dip 
through  the  Carboniferous  limestones  under  a  coal-measure 
cover.  This  earlier  circulation  seems  to  have  been  more  im- 
portant in  bringing  about  the  recrystallization  of  the  limestone, 
and  probably  to  some  extent  its  replacement  by  chert,  than  in 
causing  actual  ore-deposition.  The  coal-measure  cover  is  now, 
however,  cut  through.  The  present  actual  difference  in  head 
is  about  700  ft.  Water  now  rises  in  the  Carthage  well  from 
the  Silurian  limestones  to  within  a  few  feet  of  the  surface,  and 
in  the  Redell  deep-rock  well,  at  Joplin,  to  within  80  ft.  of  the 
surface. 

That  the  ore-bodies  wer»  deposited  by  waters  rising  from 
these  deeper  limestones  is  proved  by  the  following  facts  : 

(a)  The  ores  are  everywhere  associated  with  great  quantities 

*  Leverett,  F.,  U.  S.  GeoL  Surv.,  Monograph  xxxviii.,  pp.  550-784.  Norton, 
W.  H.,  Iowa  GeoL  Surv.,  vol.  vi.,  pp.  115-428. 

f  See  especially  A.  Winslow,  Mo.  Geol.  Surv.,  vols.  vi.  and  vii.  ;  and  W.  P. 
Jenney,  Trans.,  xxii.,  171-225. 


624  THE    GENESIS    OF    ORE-DEPOSITS. 

of  dolomite.  The  lower  limestones  are  dolomitic,  while  the 
Carboniferous  limestones  (the  immediate  country-rock)  are  not. 
It  is  also  true  that  the  Carboniferous  limestones  show  no 
dolomitization  away  from  the  region  of  the  ore-bodies,  even 
though  they  have  clearly  been  worked  over  by  circulating 
water.  The  magnesia  was  evidently  brought  in  at  the  same 
time  as  the  ores.  The  magnesian  limestones  of  the  Siluro- 
Cambrian,  in  both  the  upper  and  the  lower  Mississippi  regions, 
are  almost  everywhere  associated  with  more  or  less  ore.  The 
Carboniferous  rion-magnesian  limestones  are  nowhere  associated 
with  ore,  except  in  this  particular  region,  where,  as  has  just 
been  pointed  out,  the  circulating  waters  passed  in  their  coarse 
from  the  one  to  the  other.  These  conditions  of  circulation 
have  been  stable  for  a  long  time. 

(b)  The  ore-bodies  of  the  Joplin  region  stand  in  relations, 
usually  close,  with  a  system  of  fractures  and  faults  of  such 
extent  and  character  that  we  cannot  but  assume  that  they  have 
broken  the  underlying  Eureka-Kinderhook  shale  and  allowed 
the  intermingling  of  the  two  circulations  above  and  below  it. 
These  fracture-  and  fault-planes  have  been  much  obscured  by 
the  irregular  manner  in  which  the  Carboniferous  limestone  and 
its  contained  chert  breaks  up,  and  the  very  considerable  solu- 
tion which  has  taken  place  in  this  limestone.  Nevertheless 
faults  occur,  of  a  minimum  throw  of  80  ft.,  traceable  across 
the  country  for  a  mile  and  a  half,  and  are  not  to  be  confused 
with  the  effects  of  mere  settling  as  a  result  of  surface-solu- 
tion. Neither  are  faults  of  140  ft.  throw,  accompanied  by  over- 
thrust,  to  be  referred  to  this  category,  or  confounded  with  the 
effects  of  the  pre-coal-measure  period  of  erosion.  Such  faults 
were  present  before  the  concentration  of  the  ore ;  and  the  ore- 
bodies  stand  in  close  relations  with  them.  They  served  as  the 
main  channels  for  the  upward  flow  of  the  ore-bearing  waters. 
Once  in  the  Carboniferous  limestones,  the  solutions  wandered 
widely,  and  deposited  ore  under  many  different  conditions. 

In  the  upper  Mississippi  region,  the  fact  of  general  artesian 
conditions  on  the  flanks  of  the  Wisconsin  axis  is  well  recognized. 
The  presence  of  alternating  pervious  and  impervious  beds 
affords  several  distinct  circulations,  one  above  the  other.  Dif- 
ferences in  pressure,  composition  of  the  waters,  etc.,  indicate, 
so  far  at  least  as  the  territory  west  of  the  Mississippi  has  been 


THE    GENESIS    OF    ORE-DEPOSITS.  625 

studied,  that  each  circulation  is  practically  distinct.  The  ores 
of  the  region  are  mainly  found  in  the  Galena-Trenton  lime- 
stone, and  especially  in  the  upper,  dolomitic  portion,  to  which 
the  name  Galena  is  specifically  applied.  This  lies  below  a 
heavy  bed  of  practically  impervious  shale,  to  which  the  terms 
Maquoketa,  Cincinnati,  and  Hudson  Kiver  are  variously  applied. 
There  are  minor  and  local  beds  of  shale  in  the  Galena-Trenton, 
and  a  thin  but  persistent  bed  cuts  it  off  from  the  St.  Peter 
sandstone  below.  At  an  earlier  period,  •  as  Prof.  Van  Hise 
shows,  the  waters  in  the  Galena-Trenton  were  under  hydrostatic 
pressure;  but  now  erosion  has  cut  deep  into  and  through  the 
ore-bearing  strata,  and  for  a  long  period  of  time  the  movement 
of  the  waters  and  the  concentration  of  the  ores  has  been  down- 
ward. There  are  locally -evidences  of  movement  in  the  oppo- 
site direction,  as  at  the  Kane  Brothers'  mine  near  Dubuque; 
and  throughout  the  district  there  are  certain  phenomena  which 
are  best  explained  by  the  suggestion  of  an  earlier  concentration 
by  water  under  considerable  head.  The  later  effects  of  present 
conditions,  however,  are,  in  most  of  the  Iowa  mines,  the  more 
striking. 

Prof.  Van  Hise  has  emphasized  the  importance  of  the  imper- 
vious layer,  not  only  as  directing  the  general  course  of  under- 
ground circulation,  but  often  as  closely  connected  with  the 
deposition  of  the  ore.  In  both  the  regions  under  discussion 
examples  of  this  phenomenon  are  exceedingly  common.  In 
the  Joplin  region  the  constant  association  of  ore  with  the  small 
outliers  of  coal-measure  shale,  and  the  common  tendency  of  the 
ore  in  soft  ground  to  "  make  "  against  a  bar,  are  essentially 
phenomena  of  this  sort. 

Decrease  of  temperature  and  pressure  cannot  be  invoked  to 
explain  the  ore-bodies  in  either  region.  There  are  neither  hot 
nor  warm  springs  in  either,  nor  is  there  any  independent  evi- 
dence that  any  such  have  ever  existed.  The  reactions  involved 
in  the  genesis  of  the  ores  are  all  such  as  take  place  under 
present  surface-conditions ;  and,  when  the  time  and  quantity  of 
water  are  taken  into  account,  there  is  no  necessity  for  other 
agents.  In  the  Dubuque  (Iowa)  region,  studies  of  the  artesian 
wells  make  it  clear  that  the  circulation  did  not  extend  to  a 
depth  sufficient  to  make  pressure  quantitatively  important.  In 
Missouri,  if  the  waters  be  limited  practically  in  their  lower 


626  THE    GENESIS    OF    ORE-DEPOSITS. 

circulation  by  the  crystalline  rocks,  the  same  is  true.  There  is 
no  independent  evidence  that  any  considerable  portion  of  the 
circulation  extends  into  the  crystallines ;  and  many  facts  sug- 
gest the  opposite  view. 

The  mingling  of  solutions  has  been  especially  important  in 
producing  deposition  in  both  regions.  In  the  Dubuque  and 
Wisconsin  regions,  this  is  shown  in  the  fact  that  the  main  ore- 
deposits  are  found  at  points  where  two  crevices  cross  each 
other.  For  instance,  in  the  Stewart's  Cave  mine,  near  Dubuque, 
there  are  two  parallel  E-W.  crevices,  about  60  ft.  apart.  Along 
the  south  crevice  a  great  deal  of  lead  has  been  found;  in  the 
north  crevice,  practically  none.  In  the  south  crevice,  ore  is 
found  only  at  points  where  there  are  cross-crevices.  In  fact, 
the  south  crevice  always  carries  ore  where  there  wras  a  chance 
for  the  waters  from  the  other  crevice  to  come  in.  In  this  case, 
one  crevice  evidently  carried  the  solution  which  contained  the 
mineral,  and  the  other  the  precipitating  agent.  Where  the 
two  solutions  came  together,  an  ore-deposit  was  formed. 

In  the  Joplin  region,  the  same  thing  was  clearly  shown  in 
the  fact  that  the  great  deposits  of  zinc  are  found  largely  in  the 
Carboniferous  limestones,  which  are  cut  off  from  the  Cambro- 
Silurian  by  a  series  of  shale  beds.  It  is  only  where  these 
have  been  broken  across  by  faults  that  ore-deposits  are  found. 
The  Carboniferous  limestone  carries  large  amounts  of  bitu- 
minous matter — so  much  that,  in  certain  of  the  mines,  when 
the  rock  is  broken  it  looks  like  asphaltum-mastic.  This  bitu- 
minous matter  is  widely  distributed  throughout  the  Carbonif- 
erous limestone  of  that  region,  and  the  waters  circulating 
through  these  beds  become  highly  charged  with  it,  and  hence 
are  reducing  agents.  The  sulphate  solutions  coming  from 
below  have  been  reduced  to  sulphides  in  the  limestone,  making 
the  ore-deposits. 

The  general  principle  of  the  reduction  of  one  sulphide  by 
another  does  not  seem  to  have  been  very  important  in  the 
Missouri  region,  although  we  do  find  evidence  there  of  that 
process.  In  the  Iowa  region,  however,  it  has  played  a  very 
important  part.  At  the  Pike's  Peak,  near  Dubuque,  it  is  con- 
stantly found  that  in  the  little  cavities  in  the  rock  there  is  a 
lining  of  iron  sulphide ;  that  is,  the  iron  sulphide  is  between 
the  zinc  and  the  rock,  and  apparently  acted  as  the  reducing- 


THE    GENESIS    OF    ORE-DEPOSITS.  627 

agent.     The  iron  sulphide  was  there  first,  and  the  zinc  sul- 
phate, coming  later,  has  been  reduced  by  it  to  zinc  sulphide. 

Papers  of  Emmons  and  Weed. — The  general  principle  of  sec- 
ondary enrichment,  discussed  by  Messrs.  Emmons  and  Weed 
also  (pp.  433  and  473),  finds  exemplification  all  through  the  Jop- 
lin  region.  One  of  the  best  cases  is  the  Boston-Get-There  mine, 
at  Prosperity,  just  south  of  Cartersville.  At  this  mine  about 
15  acres  have  been  mined  out  underground,  for  a  thickness  of 
from  10  to  20  ft.  The  mine  is  in  the  top  of  a  big  body  of 
chert,  underlying  limestone.  Between  the  layers  of  original 
white  flint  are  thin  sheets  of  black  secondary  chert;  and  in 
these  bands  the  ore  is  found.  The  beds  dip  slightly  SW.,  so 
that  the  waters  falling  there,  as  shown  by  the  drainage  of 
the  mines,  flow  from  !NE.  to  SW.  Going  KE.,  up  the  dip,  we 
encounter  more  galena  and  less  zinc  blende ;  and  often  we  can 
find  where  the  little  pieces  of  zinc  blende  have  been  dissolved 
out  of  the  chert  matrix  by  the  water,  leaving  cavities  which 
have  the  characteristic  form  of  the  zinc  blende  crystals.  It 
follows  that  blende  has  been  taken  away  by  the  underground 
waters,  and  carried  down  the  dip.  Farther  down  the  dip  we 
find  cavities  filled  with  clear,  sharp  and  apparently  new  crys- 
tals of  zinc  blende.  We  have  here  an  instance  of  the  removal 
of  zinc  blende  by  the  oxidizing  waters  and  its  redeposition 
farther  down  the  dip. 

The  general  processes  of  secondary  concentration  and  enrich- 
ment are  also  exemplified  in  the  common  fact  that  the  great 
bodies  of  zinc  blende  occur  at  and  below  the  ground  water-level, 
which,  at  Joplin,  occurs  almost  at  the  surface.  Until  pumping 
was  carried  on  vigorously,  water  was  found  at  a  depth  of  about 
30  ft.  Now  the  ore  is  mined  at  depths  of  150  and  200  ft.  by 
pumping  out  the  water.  That  the  general  process,  so  far  as  the 
formation  of  the  richer  bodies  is  concerned,  has  been  one  of 
concentration  downward,  is  shown  in  the  fact  that  at  the  sur- 
face, and  in  the  small  deposits  below  the  surface,  where  we 
have  direct  evidence  of  oxidation,  we  commonly  get  galena, 
while  at  lower  depths  great  bodies  of  zinc  sulphide  occur.  Of 
the  common  sulphides,  galena,  blende  and  pyrite,  the  galena  is 
the  last  to  go  into  solution  in  the  presence  of  oxidizing  waters ; 
hence,  where  we  have  the  three  together,  the  general  effect 

40 


628  THE    GENESIS    OF    ORE-DEPOSITS. 

of  the  downward-flowing  waters  is  to  carry  the  zinc  blende 
away  from  the  galena,  leaving  the  latter  at  the  surface,  and 
redepositing  the  zinc  in  the  lower  rich  bodies  of  ore. 

Another  important  principle,  which  is  well  exemplified  in  the 
region  as  a  whole,  is,  that  the  form  and  character  of  the  ore- 
body  are  controlled  by  the  character  of  the  rock  in  which  the 
ore  occurs.  This  is  largely  due  to  the  fact  that  the  fractures  in 
rock  are  controlled  by  the  character  of  the  rock.  Homogene- 
ous rocks  will  yield  under  stress  more  uniform  fractures  than 
heterogeneous  rocks.  In  the  Joplin  region,  the  Carboniferous 
rocks  are  interbanded  limestones  and  cherts,  which  break  irreg- 
ularly ;  while  the  Cambro-Silurian  limestones  are  homogeneous, 
and  break  with  more  regular  fractures,  like  the  Wisconsin 
limestones.  The  result  is  seen  in  the  very  irregular  form  of  the 
Joplin  ore-bodies  as  contrasted  with  the  usual  regular  vein-like 
form  of  the  deposits  in  the  central,  and  portions  of  the  south- 
eastern, districts. 

The  ores  of  the  Ozark  region  in  general,  away  from  the 
southwestern  district,  were  only  studied  for  the  light  they 
would  throw  on  the  problems  of  the  latter  region.  They  are 
different  in  form,  because  they  occur  in  a  different  sort  of  rock; 
but  enough  was  seen  to  justify  the  statement  that  they  are 
quite  as  closely  dependent  upon  the  general  circulation  of  the 
underground  waters  as  are  the  Joplin  ores.  In  all  essential 
particulars  they  follow  the  same  general  principles.  The  de- 
tails of  the  investigation  naturally  cannot  be  given  here. 

DR.  CHARLES  R.  KEYES,  Des  Moines,  Iowa:  Paper  of  Van 
Hise. — It  is  not  too  much  to  say  that  Prof.  Van  Hise's  paper 
(p.  282)  marks  a  new  epoch  in  the  science  of  ore-deposits. 
Few  who  are  not  expert  petrologists,  in  the  most  modern  sense 
of  the  term,  can  fully  appreciate  the  profound  significance  of 
his  remarks.  His  paper  shows  more  conclusively  than  ever 
before  that,  if  we  are  to  make  great  advancement  in  the  study 
of  ore-deposits,  it  must  be  largely  along  geological  lines.  Geo- 
logical occurrence,  geological  structures  and  geological  rela- 
tionships come  in  for  first  consideration. 

It  is  a  startling  statement  that  ore-bodies  are  essentially  sur- 
face-deposits, that  is,  they  are  mainly  confined  to  the  brittle 
shell  of  the  globe, — that  zone  near  the  surface  commonly  called 


THE    GENESIS    OF    ORE-DEPOSITS.  629 

by  the  geologist  the  zone  of  fracture.  Few  of  us  are  fully  pre- 
pared to  accept  this  proposition  without  some  reserve.  Yet 
a  little  reflection  will  show  that  it  could  hardly  be  otherwise. 
The  phenomena  connected  with  ore-deposition  are  merely 
special  cases  of  a  more  general  problem,  with  which  geologists 
have  long  had  to  deal. 

Specially  opportune  is  Prof.  Van  Hise's  discussion  of  the  upper 
limit  of  groundwater,  concerning  the  relations  of  which  to  the 
position  and  character  of  ore-bodies,  it  removes  at  once  many 
obstacles  which  have  long  stood  in  the  way  of  satisfactory  ex- 
planation of  apparently  anomalous  phenomena.  Any  change 
of  position  of  this  groundwater  level  necessarily  produces  im- 
portant changes  in  the  mineralogical  nature  of  the  ores.  Yet 
some  orogenic  movements  are  known  to  take  place  much  more 
rapidly  than  the  ores  are  altered  by  weathering  influences ;  and 
consequently  we  often  find  a  marked  discrepancy  between  the 
groundwater-line  and  the  local  character  of  the  ores  that  we 
should  expect  to  find.  In  the  broader  field  of  general  rock- 
alteration  we  assume  the  truth  of  the  observation  made  by 
Wadsworth  that  all  such  changes  are  from  a  less  stable  to  a 
more  stable  condition.  But  this  does  not  express  the  full  sig- 
nificance of  the  phenomenon.  The  conditions  themselves  are 
continually  changing.  The  process  is  essentially  continuous, 
yet  sometimes  in  one,  and  sometimes  in  directly  the  opposite, 
direction,  as  is  the  case  with  the  better  understood  analogous 
processes  in  what  we  call  the  organic  realm. 

I  am  not  sure  that  I  fully  understand  the  statement  of  the  third 
premise  of  the  paper,  that  "  by  far  the  major  part  of  the  water 
depositing  ores  is  meteoric."  In  the  absence  of  the  full  ex- 
planation it  may  be  well  not  to  discuss  this  point.  However, 
this  statement  very  materially  broadens  our  ordinary  conception. 
There  is,  perhaps,  need  of  a  new  term  here.  But,  as  it  stands, 
and  taking  into  consideration  the  related  "  minor  part "  in  all 
its  aspects,  the  statement,  reduced  to  its  lowest  logical  terms, 
merely  declares  that  water  is  water. 

Although  Prof.  Van  Hise's  paper  contains  but  little  regard- 
ing the  classification  of  ore-deposits,  it  has  an  important  bear- 
ing upon  that  subject;  and  I  am  particularly  interested  in  this 
aspect  of  it,  because  it  is  along  the  same  line  that  I  have  been 
working  for  some  time  in  a  humble  way,  and  it  is  on  practically 


630  THE    GENESIS    OF    ORE-DEPOSITS. 

the  same  basis  that  I  presented  the  first  outlines  of  my  own 
classification  in  my  paper,  read  at  the  same  meeting  of  the  In- 
stitute.* 

When  Prof.  Van  Hise,  summing  up  the  situation,  says  that 
a  "  complete  theory  for  many  ore-deposits  must  be  a  descend- 
ing, lateral-secreting,  ascending  theory,"  he  certainly  states  a 
conclusion  from  which  there  is  no  escape.  We  can  only  attain 
an  adequate  explanation  of  ore-deposition  by  considering  all  of 
these  currents,  sometimes  working  independently,  perhaps,  but 
usually  operating  in  conjunction  and  practically  contempora- 
neously. 

In  my  own  work  I  was  confronted  by  the  labyrinthine  com- 
plexity of  any  classification  based  directly  on  the  metamorphic 
processes,  as  we  know  them  operating  upon  the  rocks.  Prof. 
Van  Hise  appears  to  be  profoundly  impressed  in  the  same 
manner. 

My  own  position  is  that  any  classification  of  ores  in  order  to 
be  useful  to  the  fullest  extent  must  be,  first  of  all,  simple; 
secondly,  capable  of  being  readily  applied  in  the  field;  and 
finally,  useful  as  a  guide  to  proper  exploitation.  No  matter 
how  refined  and  well-fitting  a  scheme  we  have,  if  it  does  not 
meet  these  three  requirements,  it  will  not  be  adopted  or  even 
be  considered  by  practical  men. 

I  need  not  here  repeat  the  further  arguments  and  explana- 
tions of  these  propositions  which  I  have  set  forth  in  my  paper, 
above-mentioned ;  and  I  content  myself  with  saying,  in  conclu- 
sion, that  if  further  progress  is  to  be  made  in  the  study  of  ore- 
deposits,  it  must  be  along  the  lines  laid  down  by  Prof.  Van  Hise. 

Paper  of  Lindgren. — We  are  certainly  deeply  indebted  to  Mr. 
Lindgren(p.  498)  for  so  excellent  a  review  of  the  subject  of  molec- 
ular interchanges  associated  with  the  production  of  ore-bodies 
occupying  fissures.  The  importance  of  considering  the  changes 
of  the  wall-rocks  of  ore-veins  has  certainly  never  been  adequately 
recognized.  Lying,  as  it  does,  in  no-man's  land,  between  the 
territory  of  the  miner  and  the  province  of  the  petrographer, 
the  subject  has  been  sadly  neglected  by  both,  instead  of  being 
made  mutually  productive. 

*  "Origin  and  Classification  of  Ore-Deposits,"  Trans.,  xxx.,  323. 


THE   GENESIS    OF   ORE-DEPOSITS.  631 

While  there  is,  no  doubt,  great  need  of  an  agreed  technical 
terminology  to  express  the  multifarious  conceptions  and  the 
various  shades  of  meaning,  I  very  much  question  the  wisdom 
of  even  attempting  to  adapt,  at  least  in  its  entirety,  the  petro- 
graphical  nomenclature,  already  well  established,  to  the  recog- 
nized phases  of  ore-formation,  where  processes  are  not  so  well 
understood,  and  exact  terminology  must  necessarily  remain 
for  some  time  yet  indefinite. 

The  meaning  commonly  ascribed  to  metasomatism,  when 
applied  to  ore-deposits,  seems  somewhat  unhappily  chosen. 
We  sometimes  get  a  clearer  insight  into  things  by  referring  to 
them  under  older  and  entirely  different  names.  The  title 
metasomatism  as  used  by  Mr.  Lindgren  is,  I  take  it,  almost, 
if  not  exactly,  co-extensive  with  the  somewhat  older  term  of 
mineralogical  metamorphism.  The  latter  term  has  been  widely 
used  by  petrographers  generally,  and  has  come  to  have  a 
special  significance  in  connection  with  the  microscopic  study 
of  rock-masses. 

So  far  as  ore-deposits  are  concerned,  these  two  terms  may 
be,  without  serious  impropriety,  regarded  as  identical  and  in- 
terchangeable. But  the  fact  should  not  be  lost  sight  of,  that 
besides  strictly  metasomatic  change,  there  are  other  grand 
groups  of  molecular  changes  among  which  may  be  mentioned, 
in  particular,  paramorphic  change.  The  latter,  while  it  may 
have  no  immediate  connection  with  ore-deposits,  has  an  ex- 
tremely interesting  mineralogical  role,  which  cannot  well  be 
overlooked,  and  which  greatly  elucidates  some  of  the  broader 
phases  of  rock-metamorphism. 

As  generally  used  by  writers  on  ore-deposits,  the  term 
metasomatism  does  not  signify  a  simple  or  definite  process,  or 
an  assemblage  of  distinct  processes.  It  is  merely  a  vague  title 
given  to  an  indeterminate  group  of  ordinary  chemical  activities, 
in  which  the  only  essential  feature  which  the  idea  carries  is 
that  each  chemical  change  is  definitely  located  in  space. 
Among  ores  it  has  special  emphasis,  for  the  reason  that  chemi- 
cal substitution  takes  place  with  the  desired  stationary  residuum. 
Emmons  succinctly  states  the  vagueness  of  the  problem  when 
he  says  that  interchange  of  substance  is  "  not  necessarily  mole- 
cule by  molecule,"  but  "  in  such  manner  as  to  preserve  the 
original  structure,  form,  or  volume  of  the  substance  replaced." 


632  THE    GENESIS    OF    OKE-DEPOSITS. 

To  illustrate  more  clearly  for  present  purposes,  we  may 
fancy  a  point  of  limestone  bathed  by  a  stream  of  moving, 
mineral-laden  water.  If  the  limestone  substance  is  gradually 
carried  away  we  have  simple  solution ;  if  from  out  the  stream 
mineral  matter  is  left  upon  the  limestone,  we  may  have  simple 
precipitation  or  incrustation ;  but  if,  as  the  molecules  of  lime- 
stone are  dissolved,  new  molecules  immediately  take  their 
places,  we  have  substitution  or  replacement.  This  last,  how- 
ever, is  not  necessarily  metasomatism,  as  I  understand  it. 

To  the  student  of  the  general  metamorphism  of  rock-masses, 
metasomatism  is  a  sharply  defined  chemical  process  by  which, 
in  the  solid  rock,  usually,  mineralogical  transformation  goes  on. 
At  least  four  well-marked  phases  are  readily  distinguished.  A 
characteristic  molecule  may  break  up  into  two  or  more,  with 
little  or  no  addition  or  substitution  of  extraneous  elements. 
Or,  there  may  be  reactions  between  adjoining  crystals  or  sub- 
stances. Or,  thirdly,  some  of  the  elements  entering  into  the 
composition  of  the  new  minerals  may  be  brought  in  from  a 
distance.  A  fourth  phase  may  occur  when  a  foreign  substance 
entirely  displaces  a  component,  molecule  by  molecule.  There 
are  still  other  distinctions  that  may  be  made  reference  to  which 
is  not  necessary  at  this  time. 

In  all  of  these  cases,  the  interchanges  are  assumed  to  take 
place  in  the  rock-mass  with  no  aid  from  circulatory  waters 
other  than  those  which  may  move  through  the  ordinary  micro- 
capillary  pores  of  the  stone. 

In  the  mineralogical  metamorphism  of  a  rock-mass  in  a 
region  undergoing  dynamic  compression,  such  as  is  initiated 
by  mountain-making  forces,  the  so-called  circulatory  under- 
ground waters  are  only  of  secondary  importance.  The  fissures 
through  which  these  waters  pass  are  relatively  local  in  influ- 
ence ;  and  changes  that  may  take  place  along  their  walls  may 
be  regarded  as  affecting  only  a  very  small  part  of  the  rock-mass 
itself. 

As  thus  understood,  it  is  doubtful  whether  ore-deposits  of 
any  considerable  extent  are  ever  really  formed  through  true 
metasomatic  action.  The  conditions  under  which  chemical 
change  goes  on  in  and  immediately  about  cavities  in  rocks 
are  so  different  from  those  under  which  the  mineralogical 
changes  in  the  rock  itself  take  place  that  it  appears  inadvisable 


THE    GENESIS    OF    ORE-DEPOSITS.  633 

to  attempt  to  extend  the  definition  of  a  term  already  well  estab- 
lished in  microscopical  petrography,  and  thereby  to  do  away 
with  its  usefulness  altogether. 

Mr.  Lindgren  himself,  I  think,  recognizes  the  force  of  this 
factor  when  he  specifically  calls  attention  to  the  wholly  distinct 
character  of  the  alteration  taking  place  in  the  body  of  the 
rock-mass  (to  certain  phases  of  which  I  have  considered  the 
term  metasomatism  restricted)  from  that  of  the  change  or  re- 
placement occurring  in  fissures,  and  says,  "  the  metasornatic 
processes  in  wall-rocks  of  the  fissure-veins  differ  generally  from 
those  of  regional  (static  and  dynamic)  metamorphism." 

The  restricted  petrographical  idea  of  metasomatism  is,  no 
doubt,  very  attractive  for  application  to  ore-deposits.  But  the 
already  widely-used  term  replacement  seems  to  cover  more 
fully  and  more  appropriately  the  analogous  phases,  as  exhibited 
by  the  ores. 

The  main  usefulness  of  the  idea  of  metasomatism,  as  applied 
to  ore-bodies,  is  to  give  rise  to  a  great  taxonomic  group  of  de- 
posits which  are  formed  often  where  no  previous  cavities  ex- 
isted, and  hence  to  set  these  off,  geologically  and  genetically, 
from  all  other  classes  of  ore-formations. 

It  is  important  to  note,  in  this  connection,  that  the  period  of 
maximum  activity  in  the  mineralogical  change  of  rock-masses 
does  not  often  coincide  with  the  period  of  maximum  ore- 
formation.  As  a  rule,  the  latter  is  long  subsequent  to  the 
former,  and  is  the  immediate  outcome  of  activities  and  condi- 
tions wholly  distinct. 

In  its  more  extended  signification,  the  term  metasomatism  is 
not  very  far  from  meaning  practically  the  same  as  chemical 
change,  at  least  so  far  as  ore-deposits  are  concerned.  In  the 
sense  intended  by  Mr.  Lindgren,  replacement  appears  to  meet 
most  nearly  the  requirements  imposed  by  the  conditions  pre- 
sented by  the  ore-deposits.  The  exact  group  of  chemical  pro- 
cesses involved,  and  the  definite  set  of  conditions  existing  in 
each  particular  case,  are  not  what  are  first  sought  in  ore-ex- 
ploitation. The  usefulness  of  the  distinction  is  really  inversely 
proportional  to  its  success  in  avoiding  expression  of  exact 
values. 

In  metasomatism  proper,  as  a  mode  of  rock-alteration  due  to 
static  or  dynamic  metamorphism,  there  are  recognized  a  num- 


634  THE    GENESIS    OF    ORE-DEPOSITS. 

ber  of  distinct  phases,  the  results  of  varying  physical  conditions 
and  differences  in  chemical  composition  and  mineralogical  con- 
stitution. Such  are  uralization,  sericitization,  saussuritization, 
epidotization,  etc.  The  suggestion  of  analogous  alterations 
due  to  contact-metamorphism,  or  in  connection  with  fissure- 
veins,  does  not  appear  to  serve  a  similar  useful  purpose  ; -  and 
in  the  special  case  of  ore-replacement  in  veins  the  central 
idea  is  completely  lost.  Topazization,  tourmalinization,  scapo- 
litization,  fluoritization,  and  the  like,  do  not,  to  my  mind,  pre- 
sent practical  features  for  the  classification  of  ore- veins,  or 
features  which  can  be  made  use  of  in  ore-exploitation. 

FRANK  D.  ADAMS,*  Montreal,  Can. :  Paper  of  Lindgren. — Mr. 
Lindgren's  paper  (p.  498)  is  a  valuable  contribution  to  the  liter- 
ature of  ore-deposits,  bringing  together  as  it  does  a  great  num- 
ber of  facts  concerning  the  metasomatic  changes  developed  by 
vein-forming  solutions  in  the  rocks  which  they  traverse.  It  is 
also  of  much  interest  as  an  attempt  to  classify  mineral  veins 
according  to  the  character  of  the  metasomatic  changes  which 
accompanied  their  development,  and  especially  according  to 
some  predominant  metasomatic  mineral,  which  they  contain. 
This  principle,  however,  as  Mr.  Lindgren  remarks,  seems  to 
have  serious  limitations  when  adopted  for  purposes  of  classifi- 
cation— one  of  these  being  the  fact  that  the  same  waters  may 
give  rise  to  different  metasomatic  minerals  in  the  case  of  dif- 
ferent rocks. 

Furthermore,  just  as  the  various  magmas  with  which  Mr. 
Lindgren  considers  the  various  kinds  of  vein-making  solutions 
to  be  severally  connected  pass  into  one  another  by  impercep- 
tible gradations,  so  do  these  solutions  also;  and  thus, instead  of 
a  series  of  well-defined  classes  of  mineral  veins,  an  almost  con- 
tinuous series  will  be  met  with  in  nature.  This  difficulty,  how- 
ever, is  shared  by  all  systems  of  petrographical  classification, 
and  by  most  of  the  other  systems  proposed  for  the  classification 
of  mineral  veins. 

In  the  case  of  the  cassiterite- veins  (Mr.  Lindgren's  Class  I.), 
for  instance,  the  predominant  metasomatic  mineral  is  said  to  be 
topaz ;  but  in  the  most  extensive  deposits  of  this  class  which 


Prof.,  McGill  University. 


THE    GENESIS    OF    ORE-DEPOSITS.  635 

are  known — those  of  Cornwall — the  predominant  metasomatic 
mineral  would  appear  rather  to  be  tourmaline. 

In  the  apatite-veins  (Class  II.),  scapolite  is  taken  as  the  pre- 
dominant metasomatic  mineral.  This  is  true  of  the  Norwegian 
deposits ;  but  in  the  Canadian  deposits,  which  are  even  more 
extensive,  while  this  mineral  is  very  common,  it  cannot  be  con- 
sidered as  predominant.  These  Canadian  deposits,  while  in 
many  cases  at  least  occurring  in  association  with  basic  igne- 
ous rocks,  as  in  Norway,  are  usually  found,  not  in  contrac- 
tion-joints of  the  intrusive  itself,  but  as  veins  cutting  the  lime- 
stones and  associated  rocks  of  the  Laurentian,  which  are 
penetrated  by  these  intrusives.  The  apatite,  unlike  that  of 
Norway,  is  a  fluor-apatite,  not  a  chlor-apatite ;  and  the  pre- 
dominant metasomatic  mineral  is  malacolite.  So  notably  is 
this  the  case  that  the  prospectors  in  the  apatite-districts  always 
look  for  "  pyroxene,"  and  regard  it  as  an  almost  certain  indi- 
cation of  phosphate  in  the  vicinity.  Next  in  abundance  to  the 
malacolite  is,  perhaps,  mica  (phlogopite  and  biotite),  which  in 
some  cases  is  present  in  such  large  amount  that  apatite-mines 
which  were  abandoned  on  account  of  the  fall  in  price  of  that 
mineral  in  the  years  1893-94  have  been,  by  reason  of  the  more 
recent  demand  for  phlogopite,  opened  up  and  worked  anew  for 
this  latter  mineral.  While,  therefore,  the  Norwegian  and  the 
Canadian  apatite-occurrences  undoubtedly  belong  to  the  same 
class  of  deposits,  the  former  is  characterized  by  the  presence 
of  chlorine  minerals,  while  in  the  latter  this  element  is  largely 
replaced  by  fluorine,  which  is  also  so  commonly  found  in  as- 
sociation with  cassiterite-veins.  The  chlorine-bearing  scapolite 
thus  cannot  be  considered  in  all  cases  as  the  predominant  meta- 
somatic mineral  required  by  the  definition  of  Class  II. 

Mr.  Lindgren's  views  concerning  the  close  genetic  associa- 
tion of  most  mineral  veins  with  igneous  masses  seem  to  be 
abundantly  supported  by  the  facts,  as  also  his  conclusions  with 
regard  to  the  preponderating  influence  of  pneumatolitic  action 
in  the  case  of  the  cassiterite-  and  apatite-veins,  as  shown  by  the 
constant  association  of  chlorine-,  fluorine-,  boron-,  phosphor- 
ous-, titanium-  and  lithium-minerals  with  them. 


636  PROBLEMS   IN   THE    GEOLOGY    OF   ORE-DEPOSITS. 


Problems  in  the  Geology  of  Ore-Deposits. 

BY   PROF.    J.    H.    L.    VOGT,    UNIVERSITY   OF   KRISTIANIA,    NORWAY.* 

(Richmond  Meeting,  February,  1901.) 
TABLE  OF    CONTENTS. 

PAGE 

INTRODUCTION,       *        *        .        .        .        .        «.      •«        *        .       -» •••'*.  636 

I.  THE  ORIGINAL  SOURCE  OF  THE  HEAVY  METALS  OF  ORE-DEPOSITS,      .     637 

Distribution  of  Elementary  Substances  in  the  Earth's  Crust,         .         .     639 

II.  THE  KELATION  BETWEEN  ERUPTIVE  PROCESSES  AND  THE  FORMATION 

OF  ORE-DEPOSITS,  ESPECIALLY  SUCH  AS  HAVE  BEEN  PRODUCED  BY 

ERUPTIVE  AFTER- ACTIONS,                 4        .        .         .         .                 .  641 

Ore-Deposits  Formed  by  Magmatic  Segregation, 642 

Ore-Deposits  Formed  by  Eruptive  After- Actions,  .         .         .         .         .643 

Cassiterite- Veins  and  Apatite- Veins, 645 

Ore-Deposits  of  Contact-Metamorphic  Origin,          ....  648 

Pyritic  Deposits, 651 

Veins  of  Gold,  Silver  and  Lead-Ore,       ......  653 

Conclusions, 658 

III.  THE  NATURE  OF  THE  ORE-SOLUTIONS  IN  VEIN-FISSURES,  AND  THE 

METASOMATIC  ALTERATIONS  ALONG  THE  ORE-VEINS,         .        .        .  658 

The  Association  of  Vein-Minerals, 658 

Deposition  of  the  Vein -Minerals,  ...         .....  659 

Alteration  of  the  Country-Eock,     .        .  .'    • .  ,        .        .         .660 

Classification  of  Metasomatic  Alterations,      .         .        »         .        .         .  660 

Additional  Observations,        .........  661 

Kaolinization,           ..........  661 

Comparison  between  Cassiterite-Veins  and  Lead-Sulphide  Veins,  .  665 
Comparison  between  Formation  of  Greisen,  etc. ,  and  Propylitiza- 

tion,  etc.,     .         .         .     .  .,' 666 

Conclusions,    .         .         .         .        .   N     .         .        .         .        .         .  668 

IV.  DIFFERENCES  OF  DEPTH  IN  THE  ORIGINAL  POSITIONS  OF  EPIGENETIC 

DEPOSITS  ;  AND  THE  SECONDARY  ALTERATIONS  OF  DEPOSITS,  .  .  669 
Original  Differences  of  Depth,  .  *  ,... .  *,.«;'  .  670 
Secondary  Alterations  of  Ore-Deposits,  ....  .  .  .  675 

INTRODUCTION. 

IN  the  latter  part  of  November,  1900,  I  received  through  the 
Secretary  of  the  Institute  the  papers  of  Messrs.  Van  Hise,  Em- 
mous,  Lindgren  and  Weed,  presented  at  the  Washington 
meeting  of  February  in  that  year,  with  the  request  (urged  also 
by  Mr.  Emmons)  that  I  would  furnish  for  the  Richmond  meet- 


*  Translated  by  the  Secretary,  and  translation  approved  by  the  Author. 


PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS.  637 

ing  a  contribution  to  the  discussion  of  the  geology  of  ore-de- 
posits, with  reference  to  these  four  papers.  It  is  a  pleasure 
and  an  honor  to  comply  with  this  request.  I  entertain  a  high 
appreciation  of  the  progress  of  the  natural  sciences  in  America 
during  the  last  half  of  the  century.  We  Europeans  realize 
that  in  many  departments  of  these  sciences  America  is  taking 
the  lead ;  and  it  is  our  desire  that  the  Old  and  the  New  World 
may  come  closer  and  closer  together  in  scientific  union.  This 
consideration  has  impelled  me  to  the  preparation  of  the  present 
paper,  for  the  deficiencies  of  which  I  must  be  permitted  to  offer 
an  excuse  in  the  fact  that  it  was  necessarily  written  within  the 
period  from  December  3  to  December  31.  In  many  respects, 
therefore,  it  is  incomplete,  because  time  was  wanting  for  a  more 
thorough  and  comprehensive  work. 

I.  THE  ORIGINAL  SOURCE  OF  THE  HEAVY  METALS  OF  ORE- 
DEPOSITS. 

It  is  well  known  that  many  investigators,  even  in  most  re- 
cent years,  have  sought  to  derive  the  heavy  metals  of  ore-de- 
posits from  the  inaccessible  interior  of  the  earth.  This  hypo- 
thesis was  favored  by  the  remarkably  high  specific  gravity 
(about  5.6)  of  the  whole  globe,  which  was  explained  by  assum- 
ing that  the  heavier  metals  were  concentrated  in  its  interior. 
A  further  confirmation  was  sought  in  the  quantity  of  iron 
found  in  meteorites,  and  also  (by  spectral  analysis)  in  the  sun. 
The  earth's  interior  was  regarded  as  a  liquid  molten  mass,  and 
the  products  of  volcanic  eruption  as  furnishing  samples  of  this 
mass,  bringing  with  them,  from  the  richly  metalliferous  hearth 
of  interior  fusion  to  the  upper  horizons,  or  even  to  the  surface, 
small  quantities  of  metals  and  metallic  compounds.  In  support 
of  this  hypothesis,  the  beautiful  synthetic  production,  by  sub- 
limation, of  cassiterite,*  specular  iron,  etc.,  performed  by 
Daubree  and  other  French  experimenters  in  the  middle  of  the 
nineteenth  century,  and  received  with  universal  and  significant 
interest,  has  often  been  cited. 

This  hypothesis  is  seductively  simple,  but  cannot  be  main- 
tained. We  must  accept  as  now  proved,  that  the  interior  of 
the  earth  cannot  be  regarded  as  a  liquid  molten  mass.  In  the 

*  According  to  the  equation,  SnCl4  -f  2H2O  =  SnO2  -f  4HC1. 


638  PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS. 

words  of  the    distinguished    Swedish    physicist,    Svante  Ar- 
rhenius,* 

' '  Modern  investigations  of  astronomers  and  physicists  show  that  the  deforma- 
tions of  the  earth's  mass  under  the  influence  of  moon  and  sun  (tides  of  the  earth's 
crust),  and  the  variations  of  the  earth's  axis  (called  precession  and  mutation)  due 
to  the  same  outside  causes,  present  such  a  quantitative  order  as  to  be  irreconcila- 
ble with  the  assumption  of  a  liquid  interior." 

He  concludes  that  the  crust  of  the  earth  is  solid  to  the  depth 
of  about  40  kilometers.  At  the  temperature  of  about  1200°  C., 
and  the  pressure  of  about  10,840  atmospheres,  existing  at  this 
depth,  most  of  the  ordinary  minerals  are  fused,  and  dissolve 
the  less  fusible  materials.  That  is  to  say,  at  the  depth  of  about 
40  kilom.  begins  a  liquid  molten  condition,  which,  however, 
cannot  continue  to  much  greater  depth.  For  at  about  300 
kilom.  the  temperature  must  without  doubt  exceed  the  critical 
temperature  of  all  known  substances;  and  at  this  point  the 
liquid  magma  passes  gradually  to  a  gaseous  magma,  subject  to 
extremely  high  pressure.  The  viscosity  and  lack  of  compressi- 
bility of  this  gaseous  magma  may  be  greater  than  those  of  the 
liquid  magma. 

We  must  give  up,  therefore,  the  old  conceptions  of  the 
earth's  interior  condition.  There  is  no  reason  for  supposing 
that  the  heavy  metals  of  ore-deposits  have  come  from  the 
enormously  compressed  earth-interior — which,  as  some  physi- 
cists declare,  must  be,  in  consequence  of  such  compression, 
"  as  hard  as  steel."  In  fact,  no  connection  has  ever  been 
shown  between  ore-deposits  and  this  heavy  interior  mass. 

We  are  forced,  then,  to  the  conclusion  that  ore-deposits  are 
derived  from  the  crust  of  the  earth — this  crust,  however,  being 
regarded  as  not  one  or  two,  but  10,  25,  or  even  50  kilometers 
thick.  Indeed,  as  will  be  shown  below,  a  notable  number  of 
ore-deposits  may  be  referred  to  eruptive  processes  connected, 
not  with  the  heavy  interior,  but  with  the  crust,  of  the  earth. 
Many  deposits,  as  Van  Hise  has  recently  shown,  are  due  to  the 
action  of  ground- water. 

Moreover,  it  has  been  shown  within  recent  decades  that 
many  elements,  formerly  regarded  as  very  rare — often  as  totally 
absent — in  rocks,  are  in  fact  almost  invariably  present  in  de- 

*  Zur  Physik  des  Vulkanismus  (Geol.  Foren.  Forh.\  Stockholm,  1900. 


PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS.  639 

tectable  (though,  of  course,  generally  minute)  quantity.  On 
this  point  I  may  mention  the  investigations  of  the  American 
chemists,  F.  "W.  Clarke  and  "W.  F.  Hillehrand,  and  also  my 
own  paper  on  the  relative  distribution  of  the  elements,  etc.,* 
from  which  I  here  introduce  a  brief  passage. 

Distribution  of  Elementary  Substances  in  the  Earth's  Crust. 

Of  the  entire  earth-crust, — namely,  the  rocks,  sea  and  at- 
mosphere,— oxygen  constitutes  by  weight  about  one-half,  and 
silicon  about  one-quarter;  the  proportions  of  aluminum,  iron, 
calcium,  magnesium,  sodium  and  potassium  range  from  10 
down  to  1  per  cent. ;  those  of  hydrogen,  titanium,  carbon  and 
chlorine  from  1  to  0.1  per  cent.;  those  of  some  eight  elements, 
phosphorus,  manganese,  sulphur,  barium,  fluorine,  nitrogen, 
pretty  certainly  also  zirconium  and  chlorine  (but  probably  no 
others,  with  the  possible  exception  of  strontium),  from  0.1  to 
0.01  per  cent.  Between  0.01  and  0.001  per  cent,  come  nickel, 
strontium  (?),  lithium,  vanadium,  bromine,  and  pretty  certainly 
also  beryllium  and  boron,  but  probably  not  tin,  cerium  and 
yttrium,  or  other  elements.  Between  0.001  and  0.0001  per 
cent,  are  cobalt,  argon,  iodine,  rubidium,  pretty  certainly  tin, 
cerium  and  yttrium,  and  possibly  also  arsenic  and  lanthanum, 
but  probably  no  others.  In  summary,  therefore,  we  have : 

Terrestrial  Distribution  of  Groups  of  Elements. 

Number  of 
Percentage.  Elements. 

10          to  1, 6 

1          "  0.1,  ...         .         .         .,       .         .         .4 

0.1       "  0.01, 8 

0.01    "  0.001,  .        .        .......     7 

0.001  "  0.0001,  „ 7 

Similar  figures  are  obtained  for  the.  intervals  -60  to  5,  5  to 
0.5,  0.5  to  0.05  per  cent.,  etc.,  proving  that  there  is  a  law  of 
quantitative  distribution  of  the  34  most  widely  occurring  ele- 
ments, according  to  which  some  4  to  8  elements  fall  within 
each  decimally-reduced  interval.  From  this  law  we  may  with 
some  confidence  further  infer  that  of  the  remaining,  say,  37 
known  elements,  some  would  fall  within  the  next  following 

*  "  Ueber  die  relative  Verbreitung  der  Elemente,  besonders  der  Schwermetatte." 
Zeitsch.  /.  prakt.  Geologic,  1898,  pp.  235,  314,  377,  413,  and  1899,  p.  10. 


040  PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS. 

smaller  intervals,  for  instance,  between  0.0001  and  0.00001,  or 
between  the  latter  and  0.000001  per  cent. 

It  may  here  be  noted  that  all  the  more  widely  distributed 
elements  (0,  Si,  Al,  Fe,  Ca,  Mg,  IsTa,  K,  H,  Ti,  C,  Cl,  P,  etc.) 
have  relatively  small  atomic  weights.  The  25  elements  having 
the  lowest  atomic  weights  (up  to  and  including  iron)  constitute  at 
least  99.8  (more  probably  99.85  to  99.9)  per  cent,  of  the  earth's 
crust,  while  the  remaining  (say)  46  elements  (among  which 
barium,  strontium,  nickel,  etc.,  are  the  most  widely  distributed) 
make  up  a  total  of  0.1,  or  at  most  0.2  per  cent.  This  is  a  re- 
sult, on  one  hand,  of  the  laws  which  controlled  the  formation 
of  the  elements  themselves,  which  are  probably  to  be  conceived 
not  as  original  and  simple  substances,  but  as  compounds ;  on 
the  other  hand,  of  those  which  controlled  the  formation  of  the 
earth-crust  from  the  original  fire-mist  of  Kant  and  Laplace. 

The  elements  of  highest  atomic  weight  are,  then,  on  the 
whole,  relatively  the  rarest  in  rocks ;  but  that  they  do  exist 
therein,  though  in  minute  proportions,  and  doubtless  in  some 
rocks  as  original  constituents,  may  be  shown,  by  way  of 
illustration,  for  the  platinum  metals. 

These  metals  are  found  here  and  there — often  together  with 
segregations  of  chromite — as  primary  segregations  formed  by 
magmatic  concentration,  in  very  basic  eruptive  rocks  (peridotite, 
and,  as  reported  in  one  locality,  highly  basic  olivin-gabbro) — a 
fact  which  clearly  indicates  their  original  presence  in  minute 
proportion  in  these  rocks.  Moreover,  in  recent  years  a  small  pro- 
portion of  platinum-metals  has  been  found  (as  at  Sudbury,  Can., 
and  Klefva,  Sweden)  in  the  segregated  sulphide-ores  of  gabbro 
rocks — a  fact  which  requires  the  supposition  that  the  gabbro 
magma  originally  contained  them.  Some  conception  of  this 
original  tenor  of  platinum-metals  may  be  formed  from  the 
statement  that  the  nick'eliferous  pyrrhotites  of  Sudbury  contain, 
according  to  many  analyses,  from  25,000  to  90,000  times  as 
much  nickel  as  platinum-metals ;  while  the  original  propor- 
tion of  nickel  in  the  gabbro  magma  may  be  set  down  as  about 
0.05  per  cent.  Hence,  on  the  (somewhat  arbitrary)  assumption 
that  the  platinum-metals  were  concentrated  from  the  magma  to 
the  same  extent  as  the  nickel,  the  magma  contained,  roughly, 
0.000001  per  cent,  of  these  metals.  This  figure,  of  course,  has 
no  pretension  to  accuracy ;  but  we  have  at  least  learned  that 


PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS.  641 

even  the  platinum-metals  are  among  the  normal  constituents  of 
the  basic  eruptive  rocks. 

It  can  be  similarly  shown  that  minute  quantities  of  gold  and 
silver  belong  in  eruptive  magmas.  For  further  discussion  of 
this  subject,  and  of  the  relative  concentration  of  certain  ele- 
ments into  the  acid,  and  of  others  into  the  basic  eruptives,  I 
refer  to  my  treatise  cited  above. 

II.    THE   KELATION   BETWEEN   ERUPTIVE   PROCESSES    AND    THE 

FORMATION  OF  ORE-DEPOSITS,  ESPECIALLY  SUCH  AS 

HAVE  BEEN  PRODUCED  BY  ERUPTIVE 

AFTER-ACTIONS. 

In  his  latest  paper,  Prof.  Van  Hise  divides  ore-deposits  into 
three  groups,  namely,  those  of  direct  igneous  origin ;  those 
which  are  the  direct  result  of  sedimentation ;  and  those  which 
have  been  deposited  by  underground  water.  His  first  and 
fundamental  premise  is  that  the  greater  number  of  ore-deposits 
are  the  work  of  underground  water.  He  asserts,  further,  that 
the  material  for  ore-deposits  is  derived  from  rocks  within  the 
"  zone  of  fracture  " ;  that  by  far  the  greater  part  of  the  water 
depositing  ores  is  meteoric ;  and  that  the  flow  of  underground 
water  is  caused  chiefly  by  gravity. 

According  to  his  view,  by  far  the  larger  number  of  ore- 
deposits  are  formed  by  underground  water,  ore-deposits  of 
direct  igneous  origin  being  "  probably  of  limited  extent."  and 
the  same  being  true  of  those  which  are  the  direct  result  of  sedi- 
mentation (some  placers,  etc.) ;  while  possibly  some  are  due  to 
sublimation.* 

In  this  paper  I  shall  not  discuss  the  sedimentary  ore-deposits ; 
but  I  may  remark  here  that,  in  my  opinion,  there  has  been,  of 
late,  a  frequent  tendency  to  underestimate  in  this  connection 
the  importance  of  sedimentation  as  a  formative  agent. 

From  Prof.  Van  Hise's  interesting  paper,  so  rich  in  new 
theoretical  suggestions,  I  have  learned  much ;  I  believe  that 
he  has  furnished  the  key  to  the  genesis  of  numerous  ore-de- 
posits ;  yet  at  the  same  time,  in  my  opinion,  he  ascribes  to  his 
theory  too  great  a  range,  and,  in  particular,  attaches  too  little 
importance  to  the  direct  genetic  relation  between  ore-deposits 

*  "Some  Principles,"  etc.,  Trans.,  xxx.,  27,  passim;  this  vol.,  pp.  282-432. 


642  PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS. 

and  eruptive  processes.  Many  of  the  occurrences  classed  by 
him  among  the  effects  of  underground  water  are,  according  to 
my  view,  the  results  of  processes  intimately  connected  with  erup- 
tive magmas,  especially  through  eruptive  after-actions  (sublima- 
tion, pneumatolysis,  pneumato-hydatogenesis,  etc.)  by  which  the 
heavy  metals  were  in  great  part  extracted  from  such  magmas. 
In  order  to  make  my  view  clear,  I  will  here  briefly  mention 
a  number  of  groups  of  ore-deposits  : 

Ore-Deposits  formed  by  Magmatic  Segregation. 

Ore-deposits  formed  by  simple  magmatic  differentiation  are 
confessedly  infrequent,  and  therefore  relatively  subordinate  in 
importance  to  other  classes.  Under  this  head  may  be  named:* 
(1)  The  occurrences  of  titanic  iron-ores  in  basic  and  interme- 
diate eruptives,  perhaps  also  of  iron-ores  in  acid  eruptives;  (2) 
those  of  chromite  in  peridotites  and  their  secondary  serpen- 
tines (and  also,  according  to  J.  H.  Pratt,  those  of  corundum  in 
the  peridotites  of  N.  C.) ;  (3)  a  number  of  deposits  of  sulphide- 
ores,  particularly  the  nickeliferous  pyrrhotites  occurring  in 
gabbro  (at  Sudbury,  Can.,  Lancaster  Gap,  Pa.,  many  places  in 
Norway  and  Sweden,  and  Varallo,  in  Piedmont) ;  (4)  according 
to  some  authorities,  the  auriferous  pyrites  of  Rossland,  B.  C.  ;f 
(5)  according  to  B.  Lotti,  the  high-grade  copper-ores  occurring 
in  serpentinized  peridotites  in  Tuscany  and  Liguria,  Northern 
Italy  (for  instance,  at  Monte  Catini),  and  analogous  occurrences 
in  other  regions;  (6)  the  occurrence  of  metallic  nickel-iron 
(without  economic  value)  in  eruptive  rocks ;  (7)  those  of  the 
platinum-metals  in  highly  basic  eruptive  rocks, J  etc.,  etc. 

It  may  be  pretty  safely  assumed  that  the  foregoing  list  will 

*  See  my  articles  in  the  Zeit.f.  prakt.  Geologic  during  1893,  1894,  1895  and  1900 
(to  be  continued  in  1901). 

f  Other  authorities  explain  the  Kossland  occurrence  differently.  See  ' c  Bio- 
titic  Gold-Copper  Veins,"  in  Mr.  Lindgren's  paper,  p.  564. 

J  Already  mentioned  on  page  640.  It  may  be  added  here  that,  so  far  as  known, 
all  primary  platinum  deposits  were  formed  by  igneous  fusion,  and  that  the  plat- 
inum-metals are  either  wholly  wanting,  or  only  exist  in  minute  traces,  in 
deposits  from  aqueous  solution.  The  latter  fact  may  be  due  to  the  small  suscep- 
tibility of  these  metals,  which  are,  for  example,  much  less  soluble  in  aqua  regia 
than  gold.  (See  Zeitsch.  f.  prakt.  Geologu,  1898,  p.  321.) 


PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS.  643 

be  enlarged  by  future  investigations,  though  it  can  never  be- 
come very  extensive.* 

Ore-Deposits  Formed  by  Eruptive  After- Actions. 

But  a  different  case  is  presented  by  deposits  connected  with 
the  eruptives  by  pneumatolytic,  pneumato-hydatogenetic,  and 
other  similar  processes,  the  heavy  metals  of  which,  as  I  con- 
ceive, were  mostly  extracted  from  the  eruptive  magmas. 

To  explain  this  proposition,  let  us  first  remark  that  the  erup- 
tive magmas — at  least  those  of  deep  origin — are  admitted  to 
be  hydato-pyrogenic — i.e.9  to  contain  a  more  or  less  notable 
admixture  of  water,  with  other  constituents  of  hydrous  or 
gaseous  character.  This  is  shown  directly  by  observations  of 
volcanoes,  and  indirectly,  for  example,  by  inference  from  the 
contact-metamorphism  along  deep  rocks,  which  is  conceived 
as  a  recrystallization  under  the  influence  of  interpenetrating 
steam.  Another  indication  is  given  by  the  enclosures  of  car- 
bonic acid  in  quartz. 

Concerning  the  chemical  and  physical  action  of  water  upon 
the  magma,  I  quote  the  following  passage  from  the  work  of 
Arrhenius,  already  cited : 

"The  water  in  the  magma  .  .  .  acts  as  an  acid  (strong  as  compared  with  silicic 
acid),  liberating  free  silicic  acid,  H2SiO3,  and  free  bases.  By  mixture  with  the 
unaltered  magma,  these  become  acid  and  basic  silicates — the  access  of  water  hav- 
ing rendered  the  magma  more  liquid." 

As  is  well  known,  the  ionization  of  water  increases  rapidly 
with  its  temperature.  This  explains  the  activity  of  water  at 
high  temperatures.  Thus,  for  example,  Barus  has  shown  that 
water  heated  above  185°  C.  attacks  the  silicates  composing 
soft  glass  with  astonishing  rapidity;  and  an  experiment  by 
Lemberg  has  proved  that  water  at  210°  C.  slowly  dissolves  an- 
hydrous powdered  silicates. 

*  Prof.  K  Beck,  in  the  first  part  (which  has  just  appeared — Berlin,  1901)  of 
his  Lehre  von  den  Erzlayerstatten,  classes  (with  some  doubt)  the  tin-ores  of  Etta 
Knob,  in  the  Black  Hills  of  Dakota,  among  magmatic  segregations.  This  seems 
to  me  incorrect.  The  deposit  mentioned,  carrying  cassiterite  with  apatite,  tri- 
phyline,  tantalite,  columbite,  spodumcne,  etc.,  presents,  in  its  mineral  paragen- 
esis  as  well  as  in  its  geological  occurrence,  all  the  distinguishing  marks  of  the  tin- 
deposits  formed  by  pneumatolytic  processes — in  this  case  intimately  connected 
with  the  eruption  of  the  granite-pegmatite.  To  this  point  I  shall  recur  later. 

41 


644  PROBLEMS    IX    THE    GEOLOGY    OF    ORE-DEPOSITS. 

Of  special  interest  in  the  study  of  pneumatolytic  phenomena 
is  the  following  passage  from  the  same  work : 

"So  far  as  we  know,  all  gases  can  be  mixed  with  each  other  in  any  desired 
proportions.  In  the  interior  gaseous  magma  of  the  earth,  therefore,  there  should 
be  no  permanent  zones  of  segregation  ;  but  all  occurring  differentiations  should 
lead  to  continuous  transitions,  and  in  the  first  rank  of  the  forces  operative  in 
these  would  be  osmotic  pressures,  of  the  detailed  nature  of  which,  at  these  high 
temperatures,  little  is  yet  known. 

"In  cooling,  however,  it  is  highly  probable  that  this  magma — at  least,  if  it 
contained  sufficient  water — separates  into  two  layers,  after  it  has  assumed  a  liquid 
state.  The  division  takes  place  at  a  proportionately  lower  temperature,  the 
smaller  the  amount  of  water.  When  this  is  very  small,  the  products  of  the 
separation  appear  only  as  enclosures  of  water,  carbonic  acid,  etc.,  at  a  very  ad- 
vanced stage  of  cooling,  when  the  mobility  is  too  small  to  permit  the  small  drops 
to  flow  together  and  form  larger  masses.  On  the  other  hand,  when  the  water- 
content  is  considerable,  the  aqueous  gas  collects  in  larger  volumes,  and  in  these 
are  concentrated  the  bodies  which,  at  the  existing  temperature,  are  more  sol- 
uble in  water  than  in  the  silicate-magma.  Among  these  bodies  are  carbonic 
acid,  hydrogen  sulphide,  combinations  of  univalent  ions,  such  as  those  of  chloric, 
fluoric  and  boric  acid,  with  the  mostly  positive  ions,  like  the  alkali-metals,  and, 
less  frequently,  the  earthy  metals,  calcium,  strontium  and  barium.  The  univa- 
lent ions  have  a  strongly  marked  tendency  to  go  to  the  water,  because  their  com- 
pounds are  dissociated  electrolytically  with  extraordinary  force.  And  among 
them  the  foremost  must  be  those  which  possess  a  strong  tendency  to  ionization, 
or,  in  the  older  chemical  phrase,  show  strong  affinity.  Those  ions,  also,  the 
hydrates  of  which  are  highly  soluble  in  water  without  becoming  dissociated,  are 
favored  in  this  process.  This  group  includes,  among  others,  the  ions  of  carbonic 
and  boric  acid  and  hydrogen  sulphide.  Of  course,  silicic  acid  is  likewise  taken 
up  by  water  in  proportion  to  its  solubility.  (The  ions  of  the  bivalent  metals — 
iron,  zinc,  lead,  copper  and  tin — seem  also  to  follow  by  preference  the  negative 
ions  named.)  In  this  solution,  composed  of  bodies  so  various,  the  positive  and 
negative  ions  are  to  be  conceived,  not  as  bound  to  each  other  in  a  definite  way, 
but  as  mutually  independent,  as  in  an  ordinary  solution,  such  as  sea-water. 

"  The  cooling  and  the  consequent  separation  into  two  layers  occur  soonest  at 
the  surface  of  contact  between  the  eruptive  and  the  cool  adjacent  rock  ;  and  it  is 
natural  to  assume  that  later  aqueous  segregations  will  by  preference  accumulate 
with  the  earlier  ones.  Other  portions  are  gradually  collected  as  geodes  and 
veins  in  the  interior  of  the  magmatic  mass.  By  reason  of  the  greatly  superior 
mobility  of  the  aqueous  solutions,  as  compared  with  the  magma,  these  segrega- 
tions may  send  out  branches  in  the  form  of  the  finest  apophyses.  The  solution 
in  aqueous  gas  now  gradually  cools,  and  one  substance  after  another  separates 
from  it.  By  reason  of  the  great  mobility  of  the  solution,  and  its  consequent 
strong  capability  of  diffusion,  the  minerals  (provided  the  cooling  be  not  too 
rapid)  are  segregated  in  large  crystals,  such  as  characterize  a  so-called  pegmatitic 
structure.  Gradually,  also,  the  constituents  which  longest  retain  a  gaseous  form 
— such  as  water  and  carbonic  acid— escape. 

"According  to  this  view,  all  the  products  required  for  the  formation  of  '  pneu- 
matolytic minerals '  are  simultaneously  present  in  the  aqueous  solution ;  and  it 
is  not  necessary  to  imagine  that  they  come  in  gaseous  form  from  different  regions, 
to  meet  at  the  point  of  segregation." 


PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS.  645 

After  this  theoretic  explanation,*  we  may  return  to  our  con- 
sideration of  the  pneumatolytic  or  pneumato-hydatogenetic  ore- 
deposits,  beginning  with  those  of  tin-ore,  the  genesis  of  which 
has  been  especially  studied  by  French  investigators,  f 

Cassiterite-  Veins  and  Apatite- Veins. — As  is  well  known,  the 
cassiterite-veins,  of  the  type  found  in  Cornwall,  the  Erzgebirge, 
Banca  and  Billiton,  Tasmania,  etc.,  are,  everywhere  in  the 
world, J  in  connection  with  acid  eruptives,  namely,  granite 
and  (now  and  then)  the  veinstones  and  ejected  rocks  of  the 
granite  family,  such  as  quartz-porphyry,  liparite  and  rhyolite. 
Partly  for  this  reason,  and  partly  because  of  the  characteristic 
paragenesis  of  the  cassiterite-veins  (presenting  many  fluoride-, 
borate-  and  phosphate-minerals),  and  the  pneumatolytic  meta- 
morphism  of  the  country-rock  (forming  Greiseri),  Elie  de  Beau- 
mont and  A.  Daubree,  as  is  well  known,  concluded  as  early  as 
1840-1850  that  these  veins  were  connected  with  the  granitic 
eruptions,  and  that  in  their  formation  various  volatile  fluorides, 
boron-compounds,  etc.,  took  part.  Daubree  was  led  to  a  de- 
tailed theory  by  his  famous  synthetic  experiments  in  sublima- 
tion. § 

The  genetic  relations  between  the  cassiterite-veins  and  the 
granite-eruptions  may  be  followed  a  step  further.  It  is  first  to 
be  emphasized  that  the  cassiterite-veins  were  formed  imme- 
diately after  the  eruption — often,  indeed,  before  the  complete 
cooling — of  the  granite.  One  proof  of  this  (among  others)  is 
the  occurrence  of  the  tin-vein-minerals  in  many  veins  of  peg- 
matite with  the  granite.  ||  It  has  been  proved  also  by  K.  Dal- 
mer  in  a  thorough  geological  study  of  the  deposits  of  the 
Erzgebirge.  And  it  follows  that,  in  this  class  of  cases,  ordinary 
underground  water  cannot  have  been  active.  We  may  assert, 
further,  that  the  cassiterite-veins  are  genetically  independent  of 
the  immediately  adjacent  country-rock. 

*  An  attempt  to  explain  the  physics  of  magmatic  differentiation  under  the  in- 
fluence of  water  dissolved  in  the  rnagma  will  be  found  in  an  article  which  I  shall 
publish  in  an  early  number  of  the  Zeit»ch.  f.  prakt.  Geologie  for  1901. 

f  The  following  statement  is  mostly  a  resume  of  my  treatise  in  the  above-named 
journal  (Nos.  4,  9,  11  and  12,  of  1895). 

|  The  peculiar  silver-tin  veins  in  Bolivia,  described  by  A.  W.  Stelzner,  are  not 
here  classed  with  tin-ore  veins  proper.  Concerning  contact-deposits  of  iron-ore 
carrying  cassiterite,  something  will  be  said  below. 

I  See  above,  p.  637.  ||  See  footnote,  p.  643,  above. 


646  PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS. 

The  geological  features  of  these  veins  force  us  to  the  view 
that  their  material  contents  were  extracted  from  the  not  yet 
fully  congealed  granite ;  and  this  view  is  confirmed  by  their 
mineralogical  and  chemical  features.  We  find  in  these  veins 
exactly  the  series  of  elements  characteristic  of  the  granite  peg- 
matite-veins, such  as  potassium  and  lithium;  also,  tin,  tung- 
sten, uranium,  niobium,  etc.,  as  well  as  beryllium  (all  also 
occurring  with  considerable  frequency  in  the  pegmatite-veins) ; 
and,  finally,  boron  and  fluorine. 

Apatite- Veins. — At  this  point,  I  will  briefly  describe  the  Nor- 
wegian and  North-Swedish  apatite-veins.  These  veins  are 
analogous  to  the  cassiterite-veins,  from  which,  however,  they 
differ  in  many  very  instructive  particulars. 

The  tin-veins  are  connected  with  granite ;  the  apatite-veins 
with  gabbro ;  and,  in  the  latter  case  also,  it  can  be  shown  that 
the  veins  were  formed  soon  after  the  eruption  of  the  rock,  and 
that  they  cannot  be  explained  by  agencies  acting  upon  the 
already  congealed  gabbro. 

In  both  classes  of  veins  we  find  a  characteristic  pneumato- 
lytic  metamorphism  of  the  country-rock.  Each  class  has  in 
abundance  a  halogen-element :  the  tin-veins  carrying  fluorine 
(with  a  very  little  chlorine),  and  the  apatite-veins  chlorine  (with 
a  very  little  fluorine),*  which  occurs  (1)  in  the  mineral  scapolite 
(containing  about  2.5  per  cent.  Cl),  abundantly  represented  in 
the  metamorphosed  zone  along  the  vein-walls  ;f  and  (2)  in  the 
mineral  chlorapatite. 

In  the  tin-veins  also,  apatite  or  other  phosphates  are  almost 
invariably  found — sometimes,  even,  in  considerable  quantity. J 
This  is  specially  noteworthy,  because  apatite  is  wholly  (or 
almost  wholly)  lacking  in  lead-silver-ore  veins,  such  as  those  of 
the  Erzgebirge,  the  Harz,  Kongsberg,  Schemnitz,  the  Comstock 
Lode,  etc.,  and  in  gold-veins  generally. 

Instead  of  the  stannic  acid,  Sn02,  found  in  the  tin-veins,  we 
find  in  the  apatite-veins  titanic  acid,  Ti02,  as  rutile  (which  is 
often  so  abundant  as  to  be  mined),  ilmenite,  titanite,  etc. 

*  The  Canadian  apatite-veins  carry  a  larger  proportion  of  fluorine  than  the 
Norwegian. 

f  In  the  well-known  apatite-deposit  at  Odegaarden,  Norway,  there  is,  on  the 
whole,  some  2.5  or  3  times  as  much  chlorine  as  phosphoric  acid. 

%  For  example,  the  cassiterite-veins  at  Montebras  in  France  are  mined  chiefly 
for  the  lithium  phosphate,  amblygonite. 


PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS.  647 

The  potassium-  and  lithium-minerals  of  the  tin-veins  are  re- 
placed in  the  apatite-veins  by  minerals  of  magnesium  and  cal- 
cium-sodium. The  apatite-veins  often  contain  some  pyrites, 
and  also,  exceptionally,  a  little  tourmaline — that  is,  a  silicate 
containing  boron. 

While  the  characteristic  elements  of  the  tin-veins  (Si,  Sn,  K, 
Li,  Be;  also  W,  Ur,  Va,  Ta,  with  F,  B,  P,  etc.)  remind  us  of 
the  composition  of  the  granite,  we  find  in  the  characteristic 
elements  of  the  apatite-veins  (especially  P,  Ti,  Fe,  Mg,  Ca,  Na, 
Cl,  etc.)  a  close  analogy  with  the  composition  of  the  gabbro. 

We  conclude  that  the  material  of  the  apatite-veins  was  ex- 
tracted from  the  gabbro  magma  in  a  manner  similar  to  that  of 
the  extraction  from  the  granite  of  the  material  of  the  tin-veins. 

Since  the  halogens  chlorine  and  fluorine  respectively  are  so 
richly  represented  in  these  two  classes  of  veins,  we  may  con- 
clude, further,  that  the  magrnatic  extraction-process  is  based 
chiefly  upon  a  reaction,  in  the  pressure  of  water,  of  hydro- 
chloric (or,  as  the  case  may  be,  hydrofluoric)  acid,  dissolved  in 
the  magma. 

In  my  work  of  1895,  cited  above,  I  have  attempted  to  prove 
that  by  such  an  "  acid  extraction-process,"  operating  in  a  granite 
magma,  especially  the  elements  K,  Li,  Be,  Sn,  W,  Ur,  ISTb,  etc., 
together  with  B  and  P,  would  be  carried  into  the  aqueous  hy- 
drofluoric solution ;  while,  on  the  other  hand,  the  aqueous 
hydrochloric  solution  in  the  gabbro  magma  would  take  up 
especially  P,  Ti,  Fe,  Mg,  Ca,  Na,  etc.  For  this  view  I  now  find 
a  support  in  the  recent  account  by  Arrhenius  of  the  chemico- 
physical  reactions  of  aqueous  magmatic  solutions. 

Pegmatite-Veins.— A  similar  argument  can  be  made  concern- 
ing the  "  nephelin-syenitic  pegmatite-veins  of  the  southwest 
border-zone  of  the  augite-syenite  region,"  near  Langesund- 
Brevig,  in  southern  Norway,  which  have  received  so  masterly 
an  examination  from  "W.  C.  Brogger.*  We  note  specially  that 
we  encounter  here  a  whole  series  of  rare  minerals,  containing 
boric,  zirconic,  stannic  and  thoric  acid  (B203,  ZrO2,  Sn02,  ThO2), 
and  also  fluorine  and  chlorine ;  and  that  Brogger  has  established 
the  following  four  phases  of  the  vein-formation  :  (1)  the  phase 
of  magmatic  solidification ;  (2)  the  principal  phase  of  pneuma- 

*  Zeitsch./.  Kryst.  u.  Min.,  vol.  xvi.,  1890. 


648  PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS. 

tolytic  solidification ;  (3)  the  phase  of  the  formation  of  zeolites ; 
(4)  the  phase  of  the  fluocarbonates,  carbonates,  etc.  We  note 
also  that  these  veins  are  to  be  considered  as  contact  phe- 
nomena.' 

Here  we  learn,  on  one  hand,  the  action  of  the  aqueous  hy- 
drochloric-hydrofluoric solution  in  the  augite-syenite  magma, 
and,  on  the  other  hand,  the  various  stages  of  the  vein-formation, 
in  which  the  influence  of  (a)  chlorides  and  fluorides,  (6)  water, 
(c)  carbonic  acid,  etc.,  is  operative. 

From  this  brief  digression  outside  the  field  of  ore-deposits, 
strictly  so  called,  we  return  to  consider 

Ore-Deposits  of  Contact- Metamorphic  Origin. — These  we  may 
more  briefly  call  "  contact-deposits,"  in  a  limited  sense  of  that 
term.  As  examples,  we  may  take  the  iron-ore  deposits  of  the 
Kristiania  region,  bordering  the  post-Silurian  (pretty  certainly 
Devonian)  granites ;  also  those  of  southern  Hungary  (at  Vasko 
or  Moravitza,  Dognaska,  etc.,  in  the  Banat),  bordering  the  late 
Mesozoic  or  Tertiary  banatite  eruptives;  also  those  of  the 
island  of  Elba,  near  Tertiary  eruptives,  particularly  granite ;  and 
those  of  Dielette,  in  the  department  of  Manche,  France.* 

The  characteristics  of  this  group  of  deposits  are : 

The  ores  (mainly  magnetite  and  specular  hematite,  yet  often 
also  sulphides  of  copper,  ]ead,  zinc,  etc.)  occur  within  the  meta- 
morphosed contact-zone  of  deep  eruptives,  especially  granite. 
Frequently  they  lie  almost  immediately  at  the  boundary  between 
the  eruptive  and  the  country-rock;  frequently  from  0.5  to  2 
kilom.  from  that  boundary,  and  sometimes  even  farther  away 
(horizontally) ;  but  never  outside  of  the  metamorphosed  zone. 
Not  seldom  they  are  found  in  fragments  of  metamorphosed  slate 
or  limestone,  which  have  torn  loose,  and  surrounded  by  the 
adjacent  eruptive. 

More  particularly,  the  ores  occur  in  limestones,  marly  slates 
and  ordinary  clay-slates,  and  are  accompanied  by  the  usual 

*  I  believe  that  numerous  ore-deposits  belong  in  this  group  of  contact-deposits. 
But  it  is  sufficient  here  to  describe  these  from  typical  representatives,  upon  the 
following  authorities  :  For  the  Kristiania  region,  the  studies  of  Th.  Kjerulf  and 
my  own  earlier  ones  (with  references  in  the  Zeitsch.  /.  prakt.  Geologic  for  1894,  pp. 
177,  464,  and  1895,  p.  154) ;  for  the  Banat  (which  I  have  also  visited  personally, 
with  Prof.  F.  Beyschlag  of  Berlin),  the  work  of  B.  v.  Cotta  (1864)  and  Edward 
Suess  (Antlitz  der  Erde)  ;  for  the  Elba  deposits,  the  investigations  of  B.  Lotti ;  and 
for  the  French  deposits,  a  description  by  Michel- LeVy. 


PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS.  649 

contact-minerals,  garnet,  vesuvianite,  scapolite,  wollastonite, 
augite,  hornblende,  mica,  etc. — and  also  (in  the  clay-slates)  by 
chiastolite,  etc.  In  other  words,  the  phenomena  of  contact- 
metamorphosis  are  the  same  here  as  elsewhere,  except  that  the 
minerals  in  the  immediate  vicinity  of  the  ores  are  developed  as 
very  large  individuals ;  i.e.9  these  ores  have  occasioned  a  con- 
tact-metamorphism  of  high  potency. 

Sometimes  the  ore-deposits  are  traversed  by  apophyses  of  the 
eruptive,  such  as  veins  of  granite,  quartz-porphyry,  etc. 

The  Kristiania  Deposits. — A  study  of  the  Kristiania  contact- 
deposits  indicates  that  the  formation  of  the  ores  preceded  the 
solidification  of  the  granitic  magma.  Even  when  the  ores  occur 
in  slates  immediately  adjacent  to  the  granite,  or  in  the  small 
Silurian  fragments  completely  surrounded  by  granite,  they  are 
never  found  also  in  the  granite  itself.  This  is  to  be  simply  ex- 
plained by  the  supposition  that  from  the  still  liquid  magma  the 
ores  were  "  blown  into  "*  the  adjoining  rigid  rocks.  If  they 
had  been  introduced  later,  they  would  have  been  deposited  in 
the  granite  also.  In  the  Kristiania  field,  the  contact-ores  are 
found  in  pre-granitic  rocks  of  all  kinds — not  only  in  limestones, 
pure  and  impure,  and  clay-slates,  but  also  in  Archean  gneiss 
and  pre-granitic  porphyry-outflows.  Hence  this  final  deposition 
is  independent  of  the  chemical  composition  of  the  adjacent 
rocks.  The  presence  in  these  deposits  of  granitic  apophyses, 
already  mentioned,  is  another  proof  that  they  were  formed  be- 
fore the  solidification  of  the  granite. 

We  conclude,  further,  that  the  material  of  the  ores  was  de- 
rived, not  from  the  surrounding  rocks,  but  from  the  eruptive 
magma.  In  the  first  place,  their  chemical  composition  (in  the 
Kristiania  region,  as  often  elsewhere,  showing  a  predominance, 
now  of  iron,  now  of  copper,  or,  again,  of  zinc,  lead,  etc.,  asso- 
ciated with  some  bismuth,  arsenic,  antimony,  etc.)  is  independ- 
ent of  that  of  the  country-rock.  In  the  second  place,  we  often 
find  the  ores  in  rock-fragments,  completely  surrounded  by  gran- 
ite^ so  small  that  they  could  not  have  furnished  the  requisite 
amount  of  ore-material. 

Contact-rnetamorphism  is  usually  referred,  in  accordance  with 

*  I  adopt  this  expression  (eingeblasen)  from  my  deceased  teacher,  Th.  Kjerulf . 
t  Of  108  old  mines  and  prospecting-pits  in  the  Kristiania  district,  16  per  cent, 
are  in  small  Silurian  masses,  completely  enclosed  in  the  granite  ;  20  per  cent,  im- 


650  PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS. 

all  probability,  to  the  action  of  heated  steam  escaping  from  the 
eruptive  magma  and  pressed  into  the  surrounding  rocks,  where 
it  produces  a  re-crystallization,  in  most  cases  without  notable 
addition  or  subtraction  of  material.  Contact  ore-deposits  form 
a  special  class  of  this  metamorphism  (involving  "  ferrization," 
etc.),  and  are  explained  by  the  presence  of  metallic  compounds 
in  the  heated  steam. 

Other  Contact-Deposits. — There  is  thus  a  close  analogy  be- 
tween such  contact  ore-deposits  as  those  of  Kristiania,  the  Banat, 
Elba,  etc.,  on  one  hand,  and  the  tin-ore  veins  on  the  other — the 
latter  being  exclusively,  and  the  former  mainly,  connected  with 
granite  eruptions.  Indeed,  there  are  also  numerous  interme- 
diate transitional  cases  between  these  two.  We  may  mention 
as  instances  the  "  tourmalinization  "  within  zones  of  contact- 
metamorphism,  well  known  in  Saxony,  and  the  similar  "axin- 
itization  "  of  contact-metamorphic  zones  in  the  Pyrenees,  which 
A.  Lacroix  has  recently  described.  In  these  cases,  that  is  to  say, 
the  boro-silicates,  so  well  known  in  tin-veins,  have  been  conveyed 
in  great  abundance  into  the  metamorphosed  zone.  Fluorspar, 
tourmaline,  axinite,  etc.,  as  well  as  the  scapolite  (which  contains 
Na  Cl),  have  also  been  found  in  our  contact-deposits  of  iron-ore ; 
while,  on  the  other  hand,  specular  iron  is  sometimes  abundant 
in  cassiterite-veins. 

Moreover,  there  are  metamorphic  contact  ore-deposits  (char- 
acterized by  garnet,  augite,  hornblende,  etc.)  which,  besides 
magnetite,  specular  hematite,  and  sulphide-ores  of  copper,  lead 
and  zinc,  carry  also  cassiterite,  with  its  usual  accompanying 
minerals.  An  instance  is  Pitkaranta  in  Finland,  where,  accord- 
ing to  A.  E.  Tornebohm,  the  order  of  deposition  was  (1)  iron- 
ore  ;  (2)  tin-ore ;  (3)  copper-ore.  Another  instance  is  furnished 
by  the  "  bed-impregnations  "  near  granite,  at  Schwarzenberg  in 
the  Erzgebirge,  recently  described  by  K.  Dalmer,*  which  carry 
as  ore-minerals  magnetite,  specular  iron,  pyrites,  galena,  zinc- 
blende,  etc.,  with  cassiterite,  wolframite,  etc.,  further  accom- 
panied by  pyroxene,  actinolite,  garnet,  epidote,  wollastoriite, 
vesuvianite,  etc.,  with  fluorite,  axinite  and  titanite.  Under 


mediately  upon  or  near  the  contact  between  these  rocks  ;  44  per  cent,  within  the 
contact-zone,  but  farther  away  from  the  granite  ;  and  20  per  cent,  in  Archean 
rock  and  pre-granitic  porphyry  overflows,  near  the  border  of  the  granite. 
*  ZeUsch.  f.prakt.  Geologiei  1897,  p.  265. 


PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS.  651 

this  head  belongs  perhaps  also  the  peculiar  occurrence  of  cas- 
siterite  and  iron-ore  in  limestone  near  Campiglia  in  Tuscany,* 
2.5  kilom.  from  a  tourmaline-bearing  granite. 

Chemical  History. — Chemically,  however,  the  processes  form- 
ing such  contact-deposits  of  iron-ore,  on  one  hand,  and  the  cas- 
siterite-veins  on  the  other,  must  have  been  different.  As  already 
observed,  the  material  of  the  latter  was  derived  through  magmatic 
extraction  by  an  aqueous  solution  of  hydrofluoric  (and  hydro- 
chloric) acid;  but  in  the  ordinary,  non-stanniferous  contact- 
deposits  of  iron-ore  the  elements  characteristic  of  the  cassiterite- 
veins  (Sn,  "W,  U,  Li,  Be,  B,  etc.)  are  almost  or  wholly  wanting, 
and,  as  a  rule,  fluorine  is  scantily  represented.  For  these  cases, 
therefore,  an  extraction  by  hydrofluoric  and  hydrochloric  acid 
is  apparently  excluded.  On  the  other  hand,  we  may  assume 
that  the  magmatic  water  itself  has  here  played  a  specially  ener- 
getic part,  and  has  extracted  iron  from  the  magma.  The  de- 
tailed explanation  is  still  an  open  question,  in  connection  with 
which  I  may  recall  the  theoretical  proposition  of  Arrhenius, 
already  quoted,  that  the  water  of  the  magma  "  acts,  relatively 
to  Si02,  as  a  strong  acid." 

Pyritic  Deposits. — As  an  appendix  to  the  foregoing  contact- 
deposits,  I  mention  the  pyritic  deposits,  typically  represented 
at  Yigsnas,  E-oros,  Sulitelma,  etc.,  in  Norway;  Rio  Tinto, 
Tharsis  and  San  Domingo,  in  Spain  and  the  adjacent  part  of 
Portugal;  Agordo  in  Lombardy  ;  Schmollnitz  in  N.Hungary; 
etc.  To  these  I  would  reckon  also  Rammelsberg  in  the  Harz. 

Concerning  the  genesis  of  these  deposits,  opinions  notori- 
ously differ.  Some  observers  assert  a  sedimentary  origin,  while, 
in  accordance  with  many  others  preceding  rne,f  I  ascribe  the 
deposits  to  after-processes,  following  eruptive  intrusions.  { 

These  deposits,  which  almost  always  have  an  apparently 
stratiform  character,  occur  only  either  in  rocks  fully  altered  by 
dynamic  metamorphism  or  in  formations  somewhat  less  power- 
fully compressed,  and,  generally,  in  close  relation  with  erup- 

*  Described  by  B.  Lotti  and  K.  Dalmer,  Zeitsch.  f.  prakt.  Geologic,  1894,  p.  400. 

f  Th.  Kjerulf  in  Norway,  K.  A.  Lessen  in  Germany,  L.  de  Launay  in  France, 
Gonzalo  y  Tarin  in  Spain,  etc. 

J  For  my  own  works  on  this  question,  see  Zeitsch.  /.  prakt.  Geologie,  1894  (Koros 
and  Rammelsberg)  and  1899  (Huelva).  I  would  mention  also  the  studies  of  F. 
Klockmann,  who  defends  the  sedimentary  hypothesis,  Id.  for  1895,  p.  35,  and 
Sitzungsb.  d.  k.  preuss.  Akad.  d.  Wiss.,  Berlin,  1894,  pp.  1173-1181. 


652  PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS. 

lives.  This  last  feature  is  highly  characteristic  of  the  numer- 
ous Norwegian  deposits  scattered  between  59°  20'  and  70°  of 
N.  lat.,  along  the  old  mountain-range  which  consists  of  Cambro- 
Silurian  slates,  probably  folded  in  the  middle  Paleozoic  (Devo- 
nian) age.  Their  distribution  is  such,  however,  that  they  ap- 
pear only  in  those  parts  of  the  range  where  considerable 
outbreaks  of  eruptive  rocks  (gabbro,  often  accompanied  by  a 
granite  rich  in  soda)  took  place,  at  about  the  period  of  the 
mountain-folding. 

Of  28  Norwegian  pyrites-deposits,  enumerated  in  my  treatise 
of  1894,  26  were  proved  to  lie  very  near,  or  actually  within, 
regions  of  compressed  gabbro.  I  can  now  add  that  in  one  of 
the  two  cases  then  excepted  we  have  found  the  eruptive  rock 
near  the  mine.  Since  the  deposits,  moreover,  are  independent 
of  the  age  of  the  slates  (mostly  phyllite-  and  mica-slates),  their 
genetic  relation  to  the  eruptives  is  indisputable. 

Some  of  them  occur  on  shearing-planes  in  the  compressed 
gabbro;  but  the  great  majority  are  in  the  slates  surrounding  it, 
most  frequently  at  a  distance  of  from  50  to  500  meters  from 
the  eruptive  border,  and  rarely  somewhat  farther  away. 

We  may  note,  further,  that  the  pyritic  deposits  themselves 
(as  has  been  shown  by  A.  W.  Stelzner  and  others)  have  some- 
times been  compressed — i.e.,  they  were  completely  formed  be- 
fore the  end  of  the  folding  of  the  mountain-chain.  Moreover, 
in  many  places  they  are  traversed  by  apophyses  of  the  erup- 
tives, i.e.,  they  were  formed  before  the  solidification  of  the 
deeper  portions  of  the  eruptive  magma. 

It  follows  from  these  considerations  that  the  Norwegian 
pyritic  deposits  are  to  be  classed  as  phenomena  of  contact- 
metamorphism  connected  with  the  gabbro  and  its  peculiar 
accompanying  granite,  and  that  their  bed-like  appearance 
must  be  explained  by  the  occurrence  of  the  gabbro  eruption 
during  the  long  period  of  mountain-folding.  The  ores  were 
thus  formed  under  extremely  high  pressure,  which  favored 
their  introduction  up  and  along  existing  planes  of  stratifica- 
tion. 

The  analogy  of  these  cases  with  those  of  the  ordinary  con- 
tact-deposits already  described  covers  also  the  origin  of  the 
ore-material,  which  we  must  assume  to  have  been  somehow 
extracted  from  the  eruptive  magma.  This  view  is  supported 


PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS.  653 

by  (1)  their  independence  of  the  adjacent  slates;  (2)  their 
formation  immediately  after  the  gabbro  eruption ;  and  (3)  the 
resemblance  of  their  material  to  that  of  the  nickel-pyrrhotite 
deposits,  considered  to  be  products  of  magmatic  secretion.  The 
chemico-mineralogical  difference  between  the  two  classes  is, 
that  in  the  magmatically  secreted  pyrrhotite  deposits  nickel 
predominates  over  copper,  while  in  the  pyritic  deposits  the 
contrary  is  the  case.  Yet  in  chemical  respects  there  exist 
complete  intermediate  transitional  occurrences,  which  I  hope  to 
describe  at  some  future  day. 

The  detailed  explanation  of  the  magmatic  extraction  form- 
ing the  pyritic  deposits  is  an  entirely  open  question ;  but  we 
may  conceive  it  to  be  the  combined  action  of  water  with  a 
sulphur-compound. 

What  I  have  said  of  the  Norwegian  pyritic  deposits  holds 
good,  I  believe,  in  its  main  features,  though  with  modifica- 
tions of  detail,  for  the  other  deposits  of  this  class,  mentioned 
above. 

Veins  of  Gold,  Silver  and  Lead-Ore. — These  may  be  divided 
into  three  main  groups :  (1)  relatively  recent  gold  and  silver, 
or  silver-lead  veins ;  (2)  old  silver-lead  veins ;  (3)  old  gold- 
veins. 

Gold-  and  Silver-  or  Silver-Lead-Veins  of  Later  Age. — As  rep- 
resentatives of  this  class  we  may  name  those  of  Nagyag- 
Yerespatak  in  Transylvania;  Schemnitz-Kremnitz  and  Nagy- 
banya-Kapnik  in  upper  Hungary  (all  of  which  lie  along  the 
Karpathian  range);  Cripple  Creek,  and  many  other  Colorado 
occurrences  in  the  Boulder,  San  Juan,  Silver  Cliff,  Rosita 
and  other  districts ;  the  Horn  Silver  and  many  mines  in  Beaver 
county,  Utah;  the  Comstock,  Esmeralda,  etc.,  in  Nevada;  and 
San  Bernardino  in  California;  the  districts  of  Durango,  Fres- 
nillo,  Zacatecas,  Guanajuato,  Pachuca,  etc., in  Mexico;  Cerro  de 
Pasco  in  Peru;  Potosi,  Huachuca,  Oruro,  etc.,  in  Bolivia,  and 
many  others  along  the  South' American  Andes;  the  Coromandel 
peninsula  (Hauraki)  in  New  Zealand ;  and,  finally,  many  places 
in  Japan.  This  list,  though  far  from  complete,  may  serve  to 
give  a  notion  of  the  wide  distribution  and  the  economic  value 
of  the  deposits  of  this  group. 

Its  general  features  were  first  described  by  F.  v.  Richthofen, 
forty  years  ago.  We  may  also  refer  here  to  the  work  of  E. 


654  PROBLEMS   IN    THE    GEOLOGY    OF    ORE-DEPOSITS. 

Suess,*  and  to  numerous  treatises  which  have  appeared  in  re- 
cent decades. 

The  younger  gold-  and  silver-veins  stand  closely  related  to 
recent  (especially  Tertiary,  but  sometimes  late  Mesozoic,  and 
occasionally  to  Quaternary)  eruptive  rocks,  f  But  they  are  not 
confined  to  any  one  of  the  recent  eruptives.  Many  occur  in 
andesites ;  others  in  dacites ;  others,  again,  in  quartz-trachytes, 
rhyolites,  etc.,  and  some  in  phonolites;  so  that  they  are  to  be 
considered  rather  as  products  of  general  volcanic  activity.  In 
fact,  they  belong,  as  a  rule,  in  each  district  to  the  latest,  or  one 
of  the  latest,  epochs  of  volcanic  activity  for  that  district.  Hot 
springs,  solfataras,  etc.,  are  frequently  found  near  them. 

Very  often  they  carry  silver  and  gold  in  combination  (Corn- 
stock,  Schemnitz,  Nagybanya-Kapnik,  etc.),  the  gold  being 
sometimes  predominant,  with  little  silver  (Cripple  Creek,  Tran- 
sylvania), and  sometimes  vice  versa  (at  many  places  in  Mexico, 
Bolivia,  etc.).  Galena  is  in  some  cases  abundant,  but  often 
almost  or  wholly  absent  (Transylvania,  Cripple  Creek,  Corn- 
stock).  Ores  of  copper  and  zinc  are,  as  a  rule,  scanty ;  arsenic 
and  antimony  pretty  common  ;  and  the  frequent  abundance  of 
arsenical  and  antimonial  sulphides  is  noteworthy. 

A  special  sub-group  is  formed  by  the  tin-bearing  silver-lead- 
bismuth-ore  veins  of  Bolivia,  examined  some  years  ago  by  A. 
"W.  Stelzner,J  which  carry  cassiterite,  and  occasionally  also  the 
sulphide,  stannite,  while  the  accompanying  minerals  usual  in 
cassiterite- veins  are  wanting.  Cassiterite  has  been  found  also 
in  some  recent  ore-veins  in  Mexico  (and  wolframite  at  Kapnik, 
Hungary). 

Tellurium  occurs  abundantly  in  some  gold-veins  (Nagyag; 
Cripple  Creek  and  other  places  in  North  America — especially 
in  Colorado ;  Hauraki,  N.  Z.),§  but  is  lacking,  wholly  or  nearly, 
in  most  cases.  Selenium  occurs  occasionally. 

The  gangue-minerals  are  chiefly  quartz  and  carbonate-spars, 
sometimes  heavy  spar  (barite).  Fluorite  is  usually  absent,  but 

*  Zukunftdes  Goldes,  1877. 

f  What  follows  is  a  summary  of  my  views  as  expressed  in  the  Zeitsch.  /.  prakt. 
Geologic,  1898,  pp.  416-420,  and  1899,  pp.  10-12. 

J  Zeitsch.  d.  d.  geol.  Gesellsch.,  Bd.  xlix.,  51  (1897).  Published  after  Stelzner's 
death  by  Bergeat. 

g  The  large  tellurium-gold-veins  at  Kalgoorlie,  W.  Aust. ,  probably  belong,  not 
to  this  younger  group,  but  to  the  older  one  above  mentioned. 


PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS.  655 

occurs  here  and  there  in  abundance,  e.g.,  in  the  celebrated  tellu- 
rium-gold field  of  Cripple  Creek,  Col.,*  and  in  the  Judith 
mountains,  Montana. 

Of  the  characteristic  alteration  of  the  country-rock  along  the 
veins  to  propylite,  with  sericite,  kaolin,  carbonate-spars,  etc., 
Mr.  Lindgren's  recent  paper  in  these  Transactions  gives  a  gen- 
eral account.  I  shall  say  more  concerning  it  in  the  next  part 
of  this  paper. 

The  Older  Lead-Silver  Veins,  and  the  Older  Gold- Veins. — 
The  lead-silver  deposits  of  Freiberg,  Annaberg  and  Schneeberg 
in  the  Erzgebirge ;  Clausthal  and  Andreasberg  in  the  Harz; 
Kongsberg  in  Norway;  Przibram  in  Bohemia,  etc.,  and  also 
the  old  gold-quartz  veins  of  the  Mother  lode  in  Gal.,  Berezowsk 
in  the  Urals,  etc.,  show  in  numerous  instances  an  undeniable 
dependence  upon  eruptive  processes  and  mountain-foldings. 
But  here  also  it  is  impossible  to  establish  a  universal  relation 
between  a  given  kind  of  vein  and  any  particular  eruptive  rock. 
The  silver-ore  veins,  for  instance,  occur  in  connection  now  with 
basic,  now  with  acid  eruptions. 

Between  these  older  and  the  younger  veins  there  are  several 
well-known  differences.  The  presence  of  both  gold  and  silver, 
in  considerable  proportions  of  each,  displayed  by  many  of  the 
more  recent  veins,  has  never  been  observed,  so  far  as  I  know, 
in  the  older  ones. 

Again,  the  older  veins  do  not  exhibit  the  propylitization  of 
the  country-rock,  so  characteristic  of  the  later  ones ;  but  there  is, 
instead,  in  many  cases,  as  described  by  Liridgren,  a  somewhat 
similar  alteration  (carbonatization  or  sericitization).  Moreover, 
the  quantity  of  sulphides  or,  generally,  of  compounds  of  arsenic, 
antimony  arid  bismuth  (and,  in  Bolivia,  of  tin)  is,  on  the  whole, 
not  so  large  in  the  older  as  in  the  later  veins. 

Yet,  notwithstanding  these  and  other  differences,  we  must, 
in  studying  the  question  of  genesis,  emphasize  rather  the  anal- 
ogies between  the  two  classes.  There  is,  for  instance,  a  signifi- 
cant similarity  in  many  respects  between  the  late  lead-silver- 

*  Some  American  observers  have  assumed  a  genetic  relation  between  fluor-spar 
and  tellurium  (or  the  telluride  gold -ores).  This  I  cannot  accept,  in  view  of  the 
absence  of  fluor-spar  from  other  gold-tellurium  districts.  There  is  no  trace  of  it 
at  Nagyag,  and,  so  far  as  I  know,  none,  or  in  any  event  very  little,  at  Kalgoorlie 
and  Hauraki. 


656  PROBLEMS   IN    THE    GEOLOGY    OF    ORE-DEPOSITS. 

gold-veins  of  Schemnitz  and  the  old  lead-silver  veins  of  Claus- 
thal;  between  Zacatecas,  Pachuca,  etc.,  in  Mexico,  and  the  "  no- 
ble "  quartz-formation  of  Freiberg,  etc.  By  reason  of  these 
mineralogical  arguments,  Prof.  R.  Beck,  in  his  new  treatise,* 
does  not  separate  the  older  and  younger  vein-groups,  but  de- 
scribes them  together  in  categories  determined  by  their  min- 
eralogical character,  such  as  the  pyritous  lead-formation,  the 
carbonate-spathic  lead-formation,  the  barytic  lead-formation,  the 
precious  (silver)  quartz-formation,  the  noble  silver-copper  for 
mation,  etc. 

In  some  cases  it  is  doubtful  whether  veins  should  be  reck- 
oned as  belonging  to  the  older  or  the  younger  group.  For  in- 
stance, the  deposits  of  Pontgibaud,  in  central  France,  show,  on 
the  one  hand,  the  character  of  the  old  galena-veins,  but  lie,  on 
the  other  hand,  not  far  from  the  late  eruptives  of  Auvergne, 
and  parallel  with  the  volcanic  fissure  of  that  field. 

As  L.  de  Launay  has  pointed  out,  it  is  quite  possible  that  the 
older  and  newer  gold-silver-lead-veins  have  a  mutual  relation 
somewhat  like  that  of  the  formerly  so-called  "  old  "  and  "young" 
eruptives,  which  are  now  distinguished  as  deep  or  outflowing, 
their  structural  differences  being  ascribed  to  crystallization  at 
different  depths.  To  this  subject  I  shall  recur  later. 

Source  of  the  Ore. — We  may  now  inquire,  Whence  comes  the 
ore  of  these  veins  ? 

For  the  older  as  well  as  the  younger  ones,  we  may  declare 
that  a  clear  genetic  connection  with  eruptive  rocks  can  be  estab- 
lished. In  some  eruptive  districts  the  latest  eruptives  of  the 
series  exposed  are  even  later  than  the  ore-veins ;  hence  the  for- 
mation of  the  latter  must  have  occurred  during  the  eruptive 
epoch. 

Partly  for  this  reason,  and  partly  because  of  the  fact  that,  on 
the  whole,  the  veins  are  generally  independent  of  the  petro- 
graphic  nature  of  the  country-rock, f  I  think  we  are  warranted, 
in  this  department  also,  in  assuming,  as  a  working-hypothesis, 
that  the  ore-material  was  extracted  from  a  magma.  With  re- 
gard to  the  younger  veins  especially,  we  must  keep  in  mind  a 
possible  extraction  from  a  laccolitic  magma  in  depth. 

*  Lehre  von  den  Erzlagerstatten,  1901. 

f  In  many  cases  there  is  a  dependence  on  the  country-rock,  the  nature  of  which 
has  favored  ore-deposition — as,  for  instance,  in  the  fahlbands  of  Kongsberg. 


PROBLEMS   IN   THE    GEOLOGY   OF    ORE-DEPOSITS.  657 

In  support  of  this  hypothesis,  we  may  cite  the  transitional  or 
intermediate  occurrences  between  the  cassiterite-  and  the  sil- 
ver-lead-veins. Thus,  in  Cornwall,  the  tin-,  the  tin-copper-  and 
the  galena-veins  are  so  closely  related  topographically  and  geo- 
logically that  a  common  origin  must  be  assumed  for  them.  The 
same  is  true  of  the  cassiterite-veins  and  the  various  silver-lead 
ore-formations  of  the  Erzgebirge ;  and  the  peculiar  tin-bearing 
silver-lead  veins  of  Bolivia  may  be  recalled  in  this  connection. 

These  intermediate  groups  warrant  the  conclusion  that  there 
can  have  been  no  absolute  essential  difference  between  the 
genesis  of  the  cassiterite-  and  that  of  the  silver-lead-veins.  If 
the  tin-veins  are  to  be  explained  by  magmatic  extraction,  the 
silver-lead  veins  may  not  be  attributable  to  the  work  of  under- 
ground water. 

We  refer,  also,  to  a  recent  paper  by  E.  Hussak,*  describing 
an  auriferous  pyritic  quartz-bed-vein  at  Passagem  in  Brazil, 
and  asserting  that  this  vein  is  to  be  considered  as  an  ultra-acid 
granitic  apophyse. 

Between  the  ordinary  quartz-veins,  deposited  from  aqueous 
solutions  (and  at  high  temperature),  and  the  granitic  apophyses, 
rich  in  aqueous  solution  and  highly  siliceous,  there  seem  to  be 
gradual  transitionary  types. 

We  may  also  recall  the  fact  that  ore-veins  often  continue  to 
a  great  depth.  As  will  be  shown  later  on,  mining  is  carried  on 
in  many  places  at  a  depth  of  not  merely  0.75  to  1.25  kilom., 
but,  in  fact,  as  referred  to  the  original  surface,  3,  4,  5,  perhaps 
6  kilom. 

The  minerals  in  veins  and  the  alterations  of  country-rocks 
show,  in  many  cases,  that  the  solutions  in  the  vein-fissures  were 
specially  rich  in  carbonic  acid  and  compounds  of  sulphur  (hy- 
drogen and  alkaline  sulphides,  sulphates,  etc.),  and  to  these  is 
often  added  an  aqueous  solution  of  silicic  acid.  As  factors  in 
magmatic  extraction  for  such  cases  we  would  assume,  therefore, 
water,  carbonic  acid,  and  compounds  of  sulphur,  and,  in  gen- 
eral, not  hydrofluoric  or  hydrochloric  acid. 

Copper-Ore  Deposits. — The  copper-ore  veins  in  or  near  eruptive 
rocks  (e.g.,  Butte,  Mont.,  and  Cornwall),  and  also  the  quicksilver- 
deposits,  permit  the  adoption  of  a  similar  genetic  hypothesis. 

*  ZeitscLf.  prakt.  Geol.,  1898,  p.  345. 


658  PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS. 

Conclusions. — That  the  ore-deposits  first  mentioned  above,  viz., 
the  titanic  iron-ores  in  gabbro,  the  chromite-occurrences  in  peri- 
clotites,  the  nickel-pyrrhotite  deposits  in  gabbro,  etc.,  were 
formed  by  magmatic  extraction,  I  think  I  have  scientifically 
proved  beyond  doubt;  and  I  believe  that  the  magmatic-extraction 
theory  advanced  for  the  cassiterite-  and  apatite-veins  is  in  its 
main  proposition  correct.  For  the  ore-deposits  subsequently 
considered — the  contact-deposits,  the  pyritic  deposits,  the  gold- 
veins,  silver-lead  veins,  copper-ore  veins,  etc. — the  views  here 
offered  become  confessedly  more  and  more  hypothetical.  But 
they  have  much  in  their  favor ;  and  even  if,  following  in  partic- 
ular the  French  observers,  I  have  here  ascribed  to  magmatic- 
extraction  too  great  a  significance,  I  believe,  nevertheless,  that 
the  hypothesis  is  worthy  of  thorough  scientific  discussion. 

At  the  same  time,  I  wish  to  add  emphatically  that,  beyond 
doubt,  numerous  ore-deposits  may  have  been  formed  by  the 
action  of  underground  waters,  so  comprehensively  investigated 
and  described  by  Van  Hise;  e.g.,  many  deposits  of  iron-  and 
manganese-ores ;  the  veins  of  nickel  silicate  (garnierite) ;  pretty 
certainly  also  the  native  copper  of  Lake  Superior ;  and  many 
other  occurrences. 

The  precise  tracing  of  the  boundary  between  eruptive  aftec- 
action  and  the  work  of  the  underground  waters  is  a  labor  for 
the  future. 

III.    THE  NATURE  OF  THE  ORE-SOLUTIONS    IN   VEIN-FISSURES, 
AND  THE  METASOMATIC  ALTERATIONS  ALONG  THE  ORE-VEINS. 

The  composition  of  these  solutions  may  be  deduced:  (1) 
from  the  association  of  minerals  in  veins,  and  their  relative 
order  of  individualization  (Breithaupt's  "  paragenesis  ") ;  and 
(2)  from  the  alteration  of  the  country-rock  proceeding  from 
the  vein-fissures. 

The  Association  of  Vein- Minerals. 

Upon  a  knowledge  of  the  quantitative  relations  among  the 
various  minerals  which  crystallized  from  the  same  solution  we 
may  base  a  conception  of  the  physico-chemical  mass-actions 
obtaining  in  the  solution.  For  example,  if  a  vein  consists 
chiefly  of  calcite,  with  a  little  silver-glance,  the  silver,  as  well  as 
the  calcium,  must  have  been  present  originally  as  AgHC03 


PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS.  659 

and  CaH2(C03)2  respectively,  in  an  aqueous  solution  of  carbonic 
acid,  from  which  it  is  pretty  certain  that  the  silver  was  precipi- 
tated by  hydrogen  sulphide.  Such  a  case  is  furnished  by  the 
deposits  of  Kongsberg,  Norway.* 

By  parallel  investigations  of  the  paragenesis  of  the  veins  and 
the  metasomatism  of  the  country-rock,  supported  by  experi- 
ments in  mineral  synthesis,  the  chemical  nature  of  vein-solu- 
tions can  be  fairly  well  determined.  The  data  at  our  disposal 
are  now  so  abundant  that  this  question  must  soon  be  ripe  for 
final  scientific  decision. 

Deposition  of  the  Vein-Minerals. 

These  have  generally  crystallized  under  high  pressure  and 
somewhat  elevated  temperature.  Under  present  conditions  a 
depth  of  1  kilom.  in  the  earth's  crust  represents  an  increase  of 
about  275  atm.  in  pressure,  and  30°  C.  in  temperature.  In 
many  ore-veins,  as  will  be  shown  later,  it  can  be  shown  that 
the  minerals  were  formed  at  a  depth  below  the  original  surface 
of  3,  4,  or  5  kilom.,  or  perhaps  more.  If  we  assume  4  kilom., 
and  conditions  like  those  of  the  present  day,  there  must  have 
been  a  pressure  of  about  1000  atm.,  and  a  temperature  about 
120°  C.  higher  than  at  the  surface. 

But  it  must  be  considered  that  in  the  exceedingly  numerous 
deposits  connected  in  some  way  with  eruptive  processes,  and 
often,  indeed,  formed  in  the  later  periods  of  the  eruptive  activ- 
ity, the  nearness  of  the  igneous  rocks  must  have  caused  an  in- 
crease of  temperature  (and  also  of  pressure  ?).  This  is  often 
so  great  as  to  exceed  for  heavy  compounds  the  "  critical  tem- 
perature," as  shown  for  a  few  substances  in  the  following  list. 

Critical   Temperatures. 

Deg.  C.  Deg.  C. 

H2O,      ....    364  HC1,  ...      52 

H2S,       ....     100  AsCls,  .        .        .356 

CO2,       ....       31  SiCl4,  ...     230 

CO,  (about)    .         .         .140  SnCl4,  .         .         .319 

SO2,       ....     157  TiCl4,  ...     358 

We  note  especially  that  the  critical  temperature  of  water 
occurs  at  364°  (or,  according  to  earlier  determinations,  375°) — 

*  See  Zeitsch.f.  prakt.  Geologic  for  April  and  May,  1899.  Concerning  the  solu- 
bility of  silver  carbonate  as  AgHCO3  in  water  containing  free  carbonic  acid,  see 
a  treatise  by  Chr.  A.  Miinster,  cited  by  P.  Krusch,  Id.,  1896,  p.  103. 

42 


660       PROBLEMS  IN  THE  GEOLOGY  OF  ORE-DEPOSITS. 

a  temperature  which  certainly  must  have  been  exceeded  by 
magmatic  solutions  at  the  moment  of  leaving  the  magma.  In 
their  upward  course — especially  determined,  perhaps,  by  their 
lower  specific  gravity — the  solutions  cool ;  and  (partly  by  vir- 
tue of  this  cooling,  and  partly  through  the  encountering  of 
various  mutually  reacting  substances)  the  minerals  are  succes- 
sively precipitated. 

Alteration  of  the  Country-Rock. 

The  scientific  study  of  this  phenomenon  of  vein-walls  was 
begun  in  the  '40s  by  Elie  de  Beaumont,  A.  Daubree  and  others; 
yet  Waldemar  Lindgren's  recent  admirable  paper*  gives  us  for 
the  first  time  a  systematic  scientific  summary  of  the  transfor- 
mations which  it  involves.  Mr.  Lindgren's  classification  of 
veins  according  to  metasomatic  processes  I  here  condense  for 
convenient  reference. 

(1)  Topaz-cassiterite  ;  (2)  scapolitic  apatite  ;  (3)  tourmalinic  gold-copper  ;  (4)bi- 
otitic  gold-copper;  (5)  propylitic  gold  and  silver;  (6)  fluoride  gold  tellurium  ; 
(7)  sericitic  and  kaolinic  gold  and  silver  ;  (8)  sericiticand  calcitic  gold  and  silver; 
(9)  silicic  and  calcitic  quicksilver^ ;  (10) .sericitic  copper-silver;  (11)  silicic  and 
dolomitic  silver-lead  ;  (12)  sideritic  silver-lead  ;  (13)  sericitic  silver-lead  ;(14)  zeo- 
litic  copper  and  silver. 

Having  busied  myself  somewhat  with  this  class  of  problems, 
I  will  take  the  liberty  to  include  here  my  attempt  at  a  classifi- 
cation of  the  metasomatic  processes  caused  by  ore-solutions. f 

Classification  of  Metasomatic  Alterations. 

1.  Alterations  forminggreisen,  mica-rock,  cassiterite-rock, 
tourmaline-rock,  topaz-rock,  etc. 

2.  Scapolitization. 

3.  Propylitizatiori  (with  chloritization,  etc.). 

4.  Kaolinization. 

5.  Sericitization. 

6.  Carbonatization  (with  dolomitization,  etc.). 


*  "Metasomatic  Processes,"  etc.,  Trans.,  xxx.,  578  ;  this  vol.,  pp.  498-612. 

f  Taken  from  the  manuscript  of  a  half-finished  paper  which  I  began  to  write 
a  year  or  two  ago.  But  I  may  refer  also  to  my  article  in  the  Zeitsch.  f.  prakt. 
Geoloyie,  Nos.  4,  11  and  12  of  1895,  and  No.  12  of  1898. 

The  term  "  carbonatization,"  which  was  new  to  me,  I  took,  a  few  years  ago,  from 
W.  Lindgren's  paper,  "Characteristic  Features  of  California  Gold-Quartz  Veins" 
(Butt.  Geol  Soc.  of  Am.,  1895,  vol.  vi.,  p.  221)  ;  and  I  now  add,  still  following 
Lindgren,  the  term  dolomitization  (as  a  process' occurring  along  ore-veins). 


PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS.  661 

7.  Silicification. 

8.  Zeolitization. 

9.  Intense  contact-metamorphism. 

I  would  mention  also  the  formation  of  alum-stone ;  quartz- 
alunite  rocks;  quartz-diaspore  rocks,  etc.  ;*  and  also  the  forma- 
tion of  bauxites,  etc.  But  I  do  not  know  that  these  changes 
have  been  anywhere  observed  in  genetic  relation  with  ore-veins. 

Between  Lindgren's  classification  and  this  one  previously 
written,  though  not  published,  by  myself,  there  is,  on  the  whole, 
a  striking  resemblance.  My  final  heading,  "  Intense  contact- 
metamorphism,"  is  not  included  byLindgren;  but  I  believe 
that  it  plays  an  important  part  in  connection,  not,  indeed,  with 
the  vein-fissures  which  he  discusses,  but  with  the  contact-de- 
posits described  in  a  previous  part  of  this  paper. 

Additional  Observations. 

To  Lindgren's  thorough  treatise  I  venture  to  add,  by  way 
of  complement  and  confirmation,  a  few  isolated  and  fragmen- 
tary observations. 

Kaolinization. — As  is  well-known,  A.  Daubreef  called  atten- 
tion to  the  fact  that  many  of  the  principal  kaolin-deposits  in 
Cornwall,  central  France  and  the  Erzgebirge  accompany  the 
tin-ore  deposits  of  those  regions.  This  may,  perhaps,  suggest 
the  idea  that  the  formation  of  kaolin,  like  that  of  cassiterite, 
must  be  explained  in  some  way  by  the  action  of  fluorides. 
Long  ago,  however,  Forchhammer  (.1835)  and  Bischoff  (1855), 
followed  by  many  more  recent  authorities,  ascribed  kaoliniza- 
tion  to  the  attack  of  water  carrying  carbonic  acid;J  and  this 
must  be  the  correct  view,  for  the  following  reasons :  (1)  kaolin- 
ization  is  in  many  cases  a  surface-process,  affected  by  the  weak 
carbonic-acid  solutions  of  surface-waters;  (2)  at  somewhat 
greater  depths,  the  feldspars  of  the  rocks  are  often  converted 
by  similarly  weak  carbonic-acid  waters  into  kaolin,  sericite,  etc., 
as  well  as  calcite.  Other  instances  may  be  given,  in  which  the 
action  of  fluorides  is  excluded. 

*  See  W.  Cross,  "Geology  of  Silver  Cliff,  etc.,  Colo.,"  and  S.  F.  Emmons, 
"  The  Mines  of  Custer  Co.,  Colo  ,"  17 ih  Ann.  Rep.  U.  S.  Geol.  Sur.,  1896. 

|  Etudes  Synthetiques  de  Geologie  Experimentale,  1879  ;  and  also  in  his  earlier 
works. 

J  For  the  literature  of  the  subject,  see  under  "  Kaolin,"  F.  Zirkel's  Lehrb.  d. 
Petrographie,  1894,  vol.  iii. 


662 


PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS. 


It  is  notoriously  orthoclase  which  is  most  frequently  con- 
verted into  kaolin.  Forchhammer  states  the  reaction  as  follows 
(in  the  old  notation,  which  I  retain) : 


Orthoclase, 
Subtracted, . 
Added,  . 

Kaolin,   . 


A1A, 


K2O,    6SiO2 
K20,    4Si02 


2H2O 


A1203, 


2Si02,     2H20 


Other  feldspars  and  silicates  of  alumina,  such  as  hornblende, 
augite,  beryl,  topaz,  etc.,  are  known  to  be  occasionally  converted 
into  kaolin ;  •  but  the  study  of  the  primary  kaolin  occurrences 
of  granite  shows  that  the  potash-feldspar  is  much  more  easily 
or  rapidly  kaolinized  than  the  silicates  of  magnesia  and  iron 
(magnesia-mica,  etc.),  while  quartz  is  attacked  but  very  weakly. 

A  few  years  ago,  near  Josingfjord,  at  Ekersund-Soggendal, 
4  or  5  kilom.  from  the  ilmenite-deposit  of  Blaafjeld-Stor- 
gaiigen,  in  southern  Norway,  a  kaolin-deposit  in  labradorite- 
rock  was  discovered,  of  such  importance  that  it  is  now  worked 
commercially.  The  kaolin  was  formed  in  situ  from  the  labrador- 
ite,  in  which  it  occurs  in  pre-glacial  fissures.  The  various 
stages  of  the  alteration  are  illustrated  by  the  following  table  of 
analyses  (hitherto  unpublished),  some  of  which,  unfortunately, 
are  not  complete  :  * 

Analyses  of  Labradorite  and  the  Products  of  its  Kaolinization. 


Labra' 
dorite. 

Labradorite, 
Partly  Kaolin- 
ized. 

Massive  Kaolin,  More  or  Less  Pure. 

Normal 
Compo- 
sition 
of  Kao- 
lin. 

I. 

II. 

'• 

II. 

III. 

IV. 

V. 

SiO*     *  

Per 
cent. 
54.5 
27.0 
2.5 
9.0 
1.0 

5.0 
1.0 

Per 
cent. 

50.03 
28.60 
1.62 
4.21 
2.95 

)  about 

r  i.oo 

11.90 

Per 

cent. 
49.16 
29.60 
1.88 
3.47 
1.67 
1  unde- 
>•  term- 
j  hied. 
13.63 

Per 
cent. 
48.61 
29.45 
3.40 
068 
0.49 
)  unde- 
>  term- 
j  ined. 
16.38 

Per 
cent. 
48.06 

}  38.57 
< 
\  unde- 
!•  term- 
|  ined. 

12.95 

Per 
cent. 

47.83 
34.53 
1.70 
0.48 
0.59 
")  unde- 
>term- 
)  ined. 
13.76 

Per 
cent. 
47.72 
37.40 
1.59 
0.23 
0.11 

0.76 
0.44 

11.66 

Per 
cent. 
46.85 
37.56 
1.00 
trace, 
trace. 
)  unde- 
Uerm- 
j  ined. 
14.44 

Per 

cent. 
46.50 
39.56 
0.00 
O.t'O 
0.00 

o.oo 

0.00 
13.94 

Al2Os 

FeoO3    .. 

Cab  

MgO 

Na20  
K2O 

H2O  

Total 

100.0 

100.31 

(99.41) 

(99.01) 

(99.58) 

(98.89) 

99.91 

(99.85) 

100.00 

NOTE. — Labradorite- rock  consists  overwhelmingly  of  labrador-feldspar  (contain- 
ing about  56.25  per  cent.  SiO.J  with  a  couple  of  per.  cent,  of  ilmenite  and  hyper- 
sthene,  somewhat  more  richly  concentrated  here  and  there  in  spots.  Hence  the 
relatively  high  percentage  of  MgO  in  Analysis  I.  of  labradorite,  and  of  Fe2O3  in 
I.  of  kaolin. 


PROBLEMS  IN  THE  GEOLOGY  OF  ORE-DEPOSITS.       663 

Taken  together  with  the  macroscopic  and  microscopic  study 
of  the  transitional  stages,  these  analyses  show:  (1)  that  ilmen- 
ite  and  hypersthene  resisted  attack  better  than  the  labrador- 
feldspar ;  and  (2)  that  from  the  latter  its  alkali-silicates  were 
extracted. 

The  larger  the  amount  of  Na2O,  K20,  CaO  and  MgO  (with 
some  Si02  and  Fe203)  removed,  the  smaller  becomes  the  specific 
gravity.  That  of  the  labradorite  unaltered  is  2.727;  of  the 
slightly  kaolinized,  2.666;  of  impure  kaolin,  still  showing  the 
feldspathic  structure  (Analysis  IY.  of  kaolin,  with  47.72  Si02), 
2.254;  of  almost  pure  kaolin,  2.193  and  2.192;  and  of  the 
purest  kaolin  of  the  district,  2.178.  These  determinations  hold 
for  the  porous  masses,  including  the  pores :  pure  non-porous 
kaolin  has  a  specific  gravity  of  2.6. 

That  in  this  case  kaolinization.  has  resulted  from  the  action 
of  carbonic  acid  waters,  follows  from  the  fact  that  occasionally, 
though  rarely,  calcite  occurs  with  the  kaolin,  while  most  of  the 
Na.20,  K20,  CaO  and  MgO  (as  soluble  carbonates),  as  well  as 
the  dissolved  Si02,  have  been  entirely  removed. 

If  I  correctly  understand  Lindgren,  he  seems,  on  pp.  614  and 
664  of  his  paper,  to  intimate  that  stronger  agents,  such  as  sul- 
phuric acid,  may  have  operated  or  co-operated  to  form  kaolin. 
In  my  judgment,  it  is  not  necessary  to  assume  such  stronger 
agents,  especially  in  view  of  the  well-known  kaolinization,  by 
ordinary  weathering,  of  the  feldspars  of  rocks.  Moreover,  sul- 
phuric and  sulphurous  acid  appear  to  produce  transformations 
of  a  different  sort  (such  as  alunite,  etc). 

As  already  remarked,  kaolin  occurs  in  some  cassiterite-veins 
(as  well  as  in  their  metasomatized  wall-rocks),  and  also  in  cer- 
tain districts  of  sulphide-ores.  Examples  are  found  at  Nagyag, 
Puda  and  other  places  in  Transylvania,  where  propylitization 
has  been  occasionally  accompanied,  in  a  subordinate  degree,  by 
kaolinization.  According  to  the  descriptions  of  Bela  von  Inkey 
and  Semper,  this  kaolinization  took  place  along  the  veins,  and 
was  independent  of  recent  weathering  by  surface-agencies.* 

*  See  B.  v.  Inkey 's  Nagy&g  u.  Seine  Lagerstatten,  Budapest,  1885  ;  and  Bergas- 
sessor  Semper' s  Beitrage  zur  Kenntniss  der  Goldlagerstatten  des  Siebenbiirgischen  Erz- 
gebirges,  in  the  Abh.  d.  preuss.  geol.  Landesanstalt,  1900,  p.  23.  According  to 
Kolebeck's  analysis  (given  in  the  Oest.  Z.f.  B.-u.  Hiittenw.,  1888,  and  referred  to 
by  Lindgren),  the  so-called  kaolin  of  Nagyag  is  in  reality  mostly  sericite  or  sericite 


664  PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS. 

This  seems  to  be  true  also  of  the  kaolinization  of  the  Cripple 
Creek  district,*  where  occasionally  not  only  granite  but  also 
phonolite  and  andesitic  breccia  have  been  transformed  to 
kaolin.  That  this  is  kaolin,  and  not  sericite,  Hillebrand's 
analyses  prove. 

Again,  at  Schemnitz,  Hungary,  according  to  some  accounts, 
propylitization  has  been  accompanied,  here  and  there,  by 
kaolinization.  For  additional  examples,  I  refer  to  Lindgren's 
paper,  under  "  Sericitic  and  Kaolinic  Gold  and  Silver  Veins," 
and  also  to  the  article  "  Kaolin  "  in  C.  Hintze's  Handbuch  der 
Mineralogie.  On  the  whole,  kaolinization  along  ore- veins  is 
rather  scanty. 

We  note,  then,  as  the  result  of  many  observations,  that  the 
formation  of  greisen  (bordering  cassiterite-veins),  and  also  pro- 
pylitization and  sericitization,  and  probably  silicification,  are 
accompanied  here  and  there  by  kaolinization,  which,  on  the 
other  hand,  seems  to  be  wholly  absent  in  cases  of  carbonatization 
(along  ore-veins),  or,  as  Lindgren  says  (p.  614) : 

"  Wherever  abundant  carbonates  form  metasomatically,  to- 
gether with  sericite,  kaolinite  seems  to  be  absent." 

Calcite  is  also,  as  a  rule,  wholly  absent  from  the  primary 
kaolin-deposits,  formed  in  situ  from  granite,  gneiss,  etc.  Even 
in  the  kaolin-deposit  of  Ekersund-Sdggendal  there  is  scarcely 
any  lime,  though  the  original  labradorite-rock  carried  consid- 
erable calcite. 

Both  kaolinization  and  carbonatization  (or  the  latter  with 
sericitization)  result  from  the  attacks  of  carbonic  acid  water, 
but  with  this  important  difference,  that  in  the  former,  lime, 
magnesia,  potash  and  soda  are  almost  or  quite  removed,  leav- 
ing the  silicate  of  alumina ;  whereas  in  the  latter,  calcite,  and 
generally  also  the  potosA-alumina  silicate,  sericite,  are  deposited 
or  precipitated.  This  difference  is  due,  pretty  certainly,  to 
quantitative  variations  in  the  constituents  of  the  attacking 
solution.  Thus,  we  learn  from  the  weathering  of  granite,  etc., 
that  very  weak  carbonic-acid  water  can  remove  lime,  magnesia, 
alkalies,  etc.,  and  produce  kaolin;  and,  on  the  other  hand,  it 

mixed  with  kaolin.  The  masses  produced  by  kaolinic  transformation,  described 
by  Semper  as  rich  in  kaolin,  calcite  and  pyrite,  probably  contain  considerable 
sericite. 

*  Messrs.  Cross  and  Pen  rose,  in  ~L6th  Ann.  Rep.  U.  S.  Geol.  Sur.,  Part  ii.,  1-209. 


PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS.  665 

may  be  assumed  that  water  rich  in  dissolved  alkaline  and  earthy 
carbonates  favors  carbonatization  and  accompanying  sericitiza- 
tion. 

Comparison  Between  Cassiterite- Veins  and  Lead-Sulphide 
Veins* — The  elder  French  school  drew  an  absolutely  sharp  line 
between  the  tin-deposits  and  the  sulphide-bearing  veins.  Some 
went  so  far  as  to  divide  all  ore-veins  into  two  classes :  (1)  the 
filons  stanniferes,  products  of  fumaroles  in  granites;  and  (2)  the 
filons  sulfur  es  ditesplombi feres,  deposited  by  thermal  springs,  and 
supposed  by  some  observers  to  be  always  connected  with  basic 
rocks.  It  is  true  that  the  typical  cassiterite-veins  (Cornwall, 
Saxony,  etc.)  are,  so  far  as  known,  connected  with  acid  eruptions 
exclusively;  but  the  converse  proposition,  that  sulphide-veins 
are  connected  with  basic  rocks  exclusively,  does  not  fit  the  facts. 
As  a  single  instance,  instar  omnium,  we  may  mention  the  im- 
mense copper-silver-ore  deposits  in  theButte  granite, in  Montana. 

The  division  into  filons  stannif&res  and  plombiferes  is  quite  fit- 
tingf — only  there  are,  here  as  elsewhere  in  nature,  no  sharp 
boundaries,  but,  on  the  contrary,  gradual  transitionary  forms. 

Among  such  transitions  we  may  mention  the  frequent  occur- 
rence in  cassiterite-veins  of  arsenopyrite  and  other  sulphide 
ores;  the  tin-copper-ore  veins  in  Cornwall;  the  connection,  in 
the  Erzgebirge  and  in  Cornwall,  between  lead-silver  veins  and 
cassiterite-veins  ;  also  the  cassiterite-bearing  lead-silver  veins  of 
Bolivia,  and  veins  in  Tellemarken,  Norway,  which  I  have  briefly 
characterized  as  "  cassiterite-veins  carrying  copper-ore  instead 
of  cassiterite."  Again,  we  may  point  out  that  tourmaline  and 
other  boro-silicates  (axinite,  datolite,  etc.)  have  often  been  ob- 
served, even  in  abundance, in  veins  carrying  sulphide  copper-ores 
or  gold.  The  general  treatises  of  A.  v.  GroddeckJ  and  A.  W. 
Stelzner,§  and  a  series  of  other  publications  (some  of  which  Lind- 
gren  cites  under  "Tourmalinic  Gold-Copper  Veins  "),  are  author- 
ities for  this  statement.  Yet,  so  far  as  I  am  aware,  galena-silver- 
ore  veins  carrying  tourmaline  in  abundance  are  not  known. 

*  The  groups  here  indicated  under  these  titles  are  those  named  by  Daubre"e,  in 
his  Eludes  Synthetiques,  etc.  (1879),  les  filons  stanniftres  and  les  filons  sulfures  dites 
plombifcres. 

f  Deposits  of  iron-  and  manganese-ore  are  not  included  in  this  classification. 

t  Zeitschr.  d.  d.  geol.  Gessellch.,  xxxix.,  78,  237  (1887). 

\  Zeitschr.  f.  prakt.  GeoL,  1897,  p.  41. 


666  PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS. 

As  a  characteristic  miner alogical  difference  between  the  two 
classes  of  veins  under  consideration  (stanniferes  and  plombiferes) 
we  may  point  out  that  topaz,  so  characteristic  of  the  former, 
has  never  been  observed,  either  in  the  ordinary  sulphide-ore 
veins  (Freiberg,  Clausthal,  etc.),  or  in  the  tourmaline-bearing 
veins,  whether  with  sulphide  copper-ores  or  with  gold.  In  the 
ordinary  sulphide-ore  veins,  moreover,  apatite  and  other  pri- 
mary phosphates  are  wanting,  as  is  also  the  lithium-mica,  so 
characteristic  of  cassiterite'-veins. 

Comparison  Between  the  Formation  of  Greisen,  etc.,  and  Propyl- 
itization,  etc. — Turning  now  to  the  metasomatism  of  the  vein- 
walls,  we  find  that  topazization  and  the  formation  of  topaz- 
greisen  are  confined  exclusively  to  cassiterite-veins.  On  the 
other  hand,  we  never  encounter,  along  these  veins,  propylitiza- 
tion,  sericitization  and  carbonatization,  which  belong  to  the 
veins  of  sulphide-ore  or  gold. 

Kaolinization,  on  the  contrary,  takes  place  (although  subor- 
dinately)  here  and  there  alongside  of  veins  of  either  kind. 
The  same  is  true  of  silicification,  as  illustrating  which  I  may 
mention  the  formation  of  "  quartz-rock  "  alongside  of  cassiterite- 
veins;  also  the  silicification  (Yerkieselung)  of  the  walls  of 
some  later  gold-veins  (as  in  a  part  of  the  Verespatak  district,, 
in  Transylvania)  and  of  some  quicksilver- veins. 

Again,  here  and  there  along  the  cassiterite-veins  as  well  as 
the  sulphide-veins,  we  find  the  country  altered  to  mica-rocks, 
which,  although  not  for  the  two  classes  mineral ogically  identi- 
cal, present  so  many  analogies  that  they  must  have  been  formed 
under  pretty  similar  conditions.  The  mica-rock  along  the 
cassiterite-veins  is  petrographically  allied  to  greisen  (arid  tin- 
or  topaz-bearing  greisen),  topaz-rock,  etc.,  and  consists  chiefly 
(or  wholly  ?)  of  lithium-mica.  On  the  other  hand,  at  Tele- 
marken,  Norway,  a  biotite-granite  is  likewise  altered  to  mica- 
rock,  along  certain  quartz-veins  carrying  chalcopyrite  or  bor- 
nite ;  but  here  the  mica,  which  appears  often  in  large  crystals, 
contains  no  lithium,  being  a  potash-mica  (muscovite).  In 
the  same  locality,  subordinate  fissures  in  the  vein-material  are 
often  lined  with  mica  crystals  (1-2  cm.  in  diameter),  exactly  as 
are  the  similar  fissures  in  the  well-known  cassiterite-deposits  of 
Zinnwald,  in  the  Erzgebirge. 


PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS.  667 

As  in  the  ordinary  alteration  to  mica-rock  and  topaz-greisen, 
so  likewise  in  propylitization  with  chloritization  and  sericitiza- 
tion,  it  is,  as  a  rule,  the  iron-magnesium-silicates  (mica,  augite, 
hornblende)  which  first  (before  the  feldspars)  suffer  alteration 
— in  other  words,  offer  the  smallest  resistance  to  the  attacking 
solutions.  On  the  other  hand,  mica,  augite  and  hornblende 
are  more  resistant  than  the  feldspars  to  the  processes  of  altera- 
tion which  form  kaolin. 

Concerning  the  alteration  of  the  later  eruptions  (andesite, 
dacite,  trachyte,  rhyolite,  etc.,  sometimes  also  basalt)  to  propy- 
lite,  I  would  refer  in  particular  to  the  well-known  monograph 
of  G.  F.  Becker  on  the  Comstock  Lode  (1882),  and  the  investi- 
gations of  B.  v.  Inkey,  Dolter,  Judd,  Koch,  Szabo  and  many 
others.* 

In  propylitization,  as  is  well  known,  the  iron-magnesium 
silicates  (augite,  hornblende,  mica,  etc.)  are  converted  chiefly 
into  chlorite,  with  sericite,  actinolite,  epidote,  serpentine,  iron 
oxides,  spathic  carbonates,  etc.  The  feldspars  lose  their  luster ; 
their  cleavage  is  impaired;  and  they  are  impregnated  with 
products  of  decomposition,  particularly  chlorite,  epidote,  cal- 
cite,  etc.  Moreover,  the  re-formation  of  pyrite  is  very  charac- 
teristic; and,  as  a  rule,  the  further  propylitization  has  pro- 
gressed, the  larger  the  quantity  of  pyrite.  Becker  has  shown 
that  this  pyrite  has  been  derived  from  the  iron-magnesium  sili- 
cates and  the  iron  oxides  (magnetite,  ilmenite,  specular  hema- 
tite) of  the  original  rock,  through  the  action  of  solutions  con- 
taining alkaline  sulphides  or  hydrogen  sulphide.f 

Rosenbusch  describes  propylitization  as  "  a  process  of  solfata- 
ric  and  thermal J  alteration."  Nearly  related  to  it  are  chloritiza- 
tion and  sericitization.  It  is  confined  to  later  ore-veins,  con- 
nected with  extensive  rocks,  and  is  absent  in  the  corresponding 
veins  of  earlier  origin.  Possibly  the  reason  of  this  difference 

*  See  chapters  on  propylite  in  Kosenbusch's  Microsc.  Physiogr.  d.  mass.  Gesteine 
(1896),  ii.,  pp.  913-917  ;  ZirkePs  Lehrb.  d.  Petrographie  (1894),  ii.,  pp.  584-595; 
and  on  "  Propylitic  Gold-  and  Silver-Veins"  in  Lindgren's  paper,  this  vol.,  p.  565. 

t  Here  we  are  reminded  of  the  chemical  nature  of  the  solutions  of  the  recent 
quicksilver-deposits  at  Steamboat  Springs,  Sulphur  Bank,  etc.  (investigated  by 
Becker  and  others),  where  the  quicksilver  is  found  combined  with  a  sodium  sul- 
phide, HgS,  nNajS. 

£  SECRETARY'S  NOTE. — I  understand  this  term,  as  used  in  German,  to  mean 
the  action  of  heated  aqueous  solutions. — R.  W.  R. 


668  PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS. 

maybe  that  the  "  old "  veins  were  formed  at  much  greater 
depths,  and  hence  under  much  higher  pressure,  whereby  the 
escape  of  solutions  (and  especially  the  dissolved  gases,  H.,8, 
etc.)  into  the  country-rock  was  hindered.  I  shall  presently 
return  to  this  point. 

A  priori,  it  is  natural  to  conceive  the  metasomatism  along 
veins  has  been  generally  accompanied  by  a  considerable  change 
(now  addition,  now  subtraction)  of  material.  This  does  indeed 
occur  in  some  instances,  especially  in  topazization,  tourmalini- 
zation  (with  axinitization)  and  kaolinization ;  but  in  many 
other  metasomatic  alterations  the  change  of  material  is  rela- 
tively insignificant.  This  is  the  case  in  scapolitization ;  in 
intense  contact-metamorphosis ;  in  many  alterations  resulting 
in  greisen  and  mica-rock;  and  also  in  propylitization  with 
chloritization  and  sericitization.  How  small,  in  the  latter 
processes,  are  the  chemical  differences  between  the  original 
and  the  altered  rock,  I  have  learned  with  astonishment  from 
the  analyses  collected  by  Lindgren. 

Conclusions. — In  conclusion,  I  will  attempt  to  give  a  summary 
of  the  agencies  operative  in  processes  of  alteration : 

1.  Topazization,  the  formation  of  topaz-greisen,  tourmalini- 
zation,  axinitization,  etc.,  are  chiefly  due  to  the  action  of  fluo- 
rides— in  the  two  latter  cases,  of  boro-fluorides. 

2.  Scapolitization  is   due  to   re-crystallization   under  high 
pressure,  with  access  of  a  chloride  (particularly  sodium  chlo- 
ride) solution.* 

3.  Propylitization  is  a  solfataric  and  thermal  alteration,  ef- 
fected by  attacks  of  hydrogen  sulphide  or  alkaline  sulphides, 
and  often  also  of  carbonic  acid. 

4.  Kaolinization,  sericitization  and  carbonatization  are  pro- 
duced by  the  action  of  waters  carrying  carbonic  acid,  or  car- 
bonates of  alkalies  and  earths,  in  variable   proportions.     (In 
kaolinization,  the  waters  carry  so  much  carbonic  acid  that  the 
alkaline  and  earthy  carbonates  are  nearly  or  wholly  removed, 
together  with  the  dissolved  silica.     In  sericitization  and  car- 
bonatization, on  the  contrary,  there  is  a  deposit  of  potassium 
silicate  or  calcium  carbonate.) 

5.  Silicification   results  from  percolation  by  a  solution  of 
silicic  acid. 

*  See,  on  this  subject,  Zeitsch.  f.  prakt.  Geol.,  1895,  pp.  447,  455. 


PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS.  669 

6.  Zeolitization  is  also  produced  by  silicic  acid,  but  under 
different  conditions  (probably,  as  a  rule,  by  a  solution  contain- 
ing silicates  of  sodium,  potassium,  calcium  and  aluminum). 

7.  Intense  contact-metamorph ism  involves  a  recrystallization 
under  bigh  pressure,  with  penetration  by  heated  aqueous  vapor, 
and  is,  per  se,  accompanied  by  a  comparatively  subordinate 
change  of  material.     Sometimes,  however,  it  occurs  in  connec- 
tion with  ferrification,  silicification,  tourmalinization  or  axiniti- 
zation,  etc. 

8.  The  formation  of  alum-stone  or  alunite  is  chiefly  effected 
by  the  penetration  into  the  rock  of  a  solution  of  sulphuric  or 
sulphurous  acid. 

Frequently  several  of  the  above  agencies  operate  in  combina- 
tion, rendering  the  results  more  complicated. 

IY.  DIFFERENCES  OF  DEPTH  IN  THE  ORIGINAL  POSITIONS  OF  EPI- 

GENETIC  DEPOSITS  ;  AND  THE  SECONDARY  ALTERATIONS 

OF  DEPOSITS. 

The  attention  of  both  miners  and  geologists  was  long  ago 
drawn  to  these  theoretically  interesting  and  economically  im- 
portant problems ;  yet  only  in  recent  years  have  they  received 
thorough  and  comprehensive  treatment.  The  valuable  contri- 
butions made  to  the  Transactions  of  this  Institute  by  Don,  Em- 
mons,  Rickard,  Posepny,  Van  Hise,  Weed  and  others,  are  fa- 
miliar to  its  members,  as  well  as  the  work  of  R.  A.  F.  Penrose 
and  his  associates  of  the  U.  S.  Geological  Survey,  and  other 
American  observers  Much  may  be  learned  from  the  recent 
treatise  of  our  celebrated  professional  colleague,  Prof.  L.  de 
Launay.* 

These  two  phenomena — namely,  the  original  differences  of 
depth  connected  with  the  formation  of  ore-deposits,  and  the 
secondary  alterations  of  such  deposits,  occurring  often,  perhaps 
even  millions  of  years  later — are  in  many  cases,  as  genetic  fac- 
tors, very  widely  separated ;  yet  it  may  often  be  difficult  to  decide 
what  is  to  be  referred  to  the  primary  and  what  to  the  secondary 
process.  Partly  for  this  reason,  and  partly  because,  as  Van 

*  ' '  Les  variations  des  filons  metallif  eres  en  profondeur ' '  (Rev.  Gen.  des  Sci.  Pures 
et  Appliquees,  xi.,  1900;  discussed  by  P.  Krusch  in  Zeitsch.  f.  prakt.  Geol.,  Oct., 
19CO).  See  also  De  Launay 's  Contribution  d,  V  etude  des  gites  metallif 'eres  in  Ann.  d. 
Mines,  9  S^rie,  vol.  xiL,  p.  119  (1897). 


670  PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS. 

Hise's  last  paper  shows,  the  two  factors  go,  in  many  localities, 
hand  in  hand,  I  think  they  may  be,  with  advantage,  discussed 
together. 

Original  Differences  of  Depth. 

In  considering  the  original  differences  of  depth,  it  mnst  be 
kept  in  mind,  as  De  Launay  has  pointed  out  in  the  treatises 
just  cited,  that  the  present  surface  is,  in  general,  very  far  below 
the  surface  existing  at  the  time  of  the  ore-formation.  The  geolog- 
ical investigations  of  recent  decades  have  shown  that  the  work 
of  denudation  (or  abrasion  or  erosion)  must  be  measured  on  a 
larger  scale  than  was  formerly  suspected.  In  the  Archean  and 
Algonkian  mountain  chains  (now  often  removed  by  this  agency 
down  to  their  base-level),  and  also  in  the  Paleozoic  ranges 
(showing,  as  a  rule,  the  effects  of  extremely  energetic  denudation, 
as,  for  example,  the  Ural  and  the  Norwegian  mountains),  the 
difference  between  original  and  present  levels  is  to  be  generally 
reckoned,  not  in  such  units  as  0.1,  0.25,  0.33  or  0.5  kilom.,  but 
rather  on  the  scale  of  2,  3,  4  or  5  kilom.,  or  even  more.  Even 
in  the  Mesozoic  and  Tertiary,  many  denudations  of  astounding 
depth  have  been  recognized.* 

In  many  epigenetic  ore-deposits  of  Archean- Algonkian  or 
Paleozoic  origin  (e.g.,  Kongsberg,  Cornwall,  Przibram,  the 
Keweenaw  peninsula  at  Lake  Superior)  mining  has  been  carried 


*  As  instances  of  great  denudation,  the  following  may  be  named  : 

On  the  E.  side  of  the  Kristiania  fiord,  in  Norway,  this  process  has  removed,  ( 1 ) 
a  series  of  Devonian  conglomerates  and  porphyry  overflows,  with  Silurian  and 
Cambrian  rocks,  of  an  aggregate  thickness  (according  to  W.  C.  Brogger,  Nyt. 
May.  f.  Naturv.j  vol.  xxxviii.,  for  1900)  of  2500  meters  ;  (2)  also  a  large  part  of 
the  Archean  surface — first,  during  the  long  pe-iod  preceding  the  Cambrian,  and 
again  after  the  removal  of  the  Cambrian,  Silurian  and  Devonian  strata.  This 
thickness  must  also  be  measured  in  thousands  of  meters ;  so  that  we  have  here 
at  least  4000,  perhaps  5000,  6000  or  even  more  meters  of  thickness  removed. 

The  fiords  of  the  W.  coast  of  Norway  are  often  1 .5,  sometimes  2  to  2. 25  kilom. 
more  deeply  eroded  than  the  adjoining  high  plateau  ;  and  the  latter  frequently 
consists  of  deep  eruptives,  without  any  remains  of  the  extensive  overflows — show- 
ing that  on  the  plateau  a  very  extensive  denudation,  probably  to  be  measured  in 
kilometers,  has  taken  place. 

In  the  Aspen  silver-district,  Colo.,  o  kilom.  of  strata  (according  to  Spurr)  have 
been  removed  by  erosion  from  a  range  of  Tertiary  origin.  (I  quote  from  Krusch's 
review  of  De  Launay,  Zeitsch.f.  prakt.  Qeol..,  1900,  p.  317.  ) 

In  California,  according  to  Lindgren,  denudation  has  extended  to  a  depth  of 
500  to  1500  or  more  meters.  So  far  as  I  know,  this  denudation  has  taken  place 
since  the  beginning  of  the  Cretaceous  period. 

Numerous  other  similar  instances  could  be  easily  adduced. 


PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS.  671 

to  depths  of  0.75,  1  to  1.25,  and  1.25  to  1.5  kilometers.  Tak- 
ing the  depth  roughly  as  1  kilom.,  and  assuming  that  in  some 
districts  the  present  surface  has  been  denuded  3,  and  in  others 
4,  kilom.  below  the  surface  at  the  time  of  the  ore-formation, 
we  may  say  that  mining  has  reached  a  depth  of  3  to  4  or  4  to 
5  kilom.  below  the  original  surface. 

These  figures  are,  of  course,  somewhat  arbitrary ;  but  mod- 
ern investigations  of  the  extent  of  denudation  justify  us  in  say- 
ing that  they  are  not  too  high  for  some  districts  belonging  to 
the  ancient  geological  periods  above  named. 

It  may  be  observed,  also,  that  in  many  deposits  of  deep  and 
geologically  old  origin,  the  deepest  portions  of  *the  mines  have 
shown  no  change  in  the  nature  of  the  fissure-formation.  Occa- 
sionally, as  at  Przibram,  Bohemia,  and  Dolcoath,  Cornwall, 
the  richest  ore-bodies  have  been  encountered  in  the  deepest 
mine-workings. 

We  conclude,  then,  that,  under  favorable  circumstances,  the 
ore-veins  may  continue  at  least  to  a  depth,  below  the  original 
surface,  of  3,  4,  5  or  more  kilometers. 

In  opposition  to  this  view,  Prof.  Beck  declares*  that  he  has 
come  to  the  opinion 

"That  ore- veins,  and  mineral  veins  generally,  can  by  no  means  extend  to 
great  depths,  geologically  speaking.  .  .  .  Even  if  we  could  assume  the  exist- 
ence, at  a  depth  between  4000  and  COOO  meters,  of  fissures  filled  with  water,  it 
would  be  inconceivable  that,  at  that  depth,  mineral  deposits  could  be  made  from 
solutions. ' ' 

I  believe,  notwithstanding,  that  future  determinations  of  the 
extent  of  denudation,  together  with  the  mining  of  many  de- 
posits to  the  depth  of  1.25, 1.5,  or  even,  perhaps,  2  kilom.  below 
the  present  surface,  will  prove  that  Prof.  Beck's  conclusion  is 
not  correct. 

It  may  also  be  remarked,  in  passing,  that  mineral  deposits 
may  be  made  from  solutions  at  above  the  critical  temperature 
(364°  C.)  of  water — for  instance,  the  deposits  of  cassiterite, 
wolframite,  apatite,  topaz,  tourmaline,  and  even  pyrites,  in  many 
granite-pegmatite  veins. 

In  his,  latest  treatise,  which  is  rich  in  new  conceptions,  De 

*  Lehre  von  den  Erzlagerstatten,  1901,  p.  139. 


672  PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS. 

Launay  compares  ore-deposits  occurring  relatively  near  the 
surface,  in  less  denuded  regions,  with  those  deep  below  the 
surface  in  strongly  denuded  regions.  As  instances  of  the 
former,  he  takes  the  quicksilver-deposits,  which  occur  chiefly 
in  recent  rocks,  near  volcanic  eruptives,  while  from  older 
ranges,  partly  destroyed  by  erosion,  they  have  disappeared, 
with  other  debris.  As  instances  of  the  latter  class,  he  takes 
the  pyritic  deposits  (Roros,  Huelva,  Schmollnitz,  etc.),  which 
have  been  found  in  old  mountain-chains  or  in  districts  of  re- 
gional metamorpHsm,  and  are  to  be  explained  as  of  deep-seated 
origin.  He  also  mentions  very  briefly  the  lead-silver  veins. 

Induced  by  his  description,  I  have  already  suggested  in  this 
paper  the  hypothesis  that  the  differences  between  the  later 
gold-silver-lead  veins  (Nagyag,  Comstock,  Potosi,  etc.)  and  the 
old  gold  and  silver-lead  veins  (Kongsberg,  Erzgebirge,  Harz, 
Przibram,  etc.)  maybe  explained  by  their  formation  at  different 
depths.  The  relative  or  total  absence  from  the  older  veins  of 
the  propylitization  which  is  so  characteristic  of  the  later  ones 
may,  perhaps,  be  due  to  the  fact  that  hydrogen  sulphide  (or 
sodium  sulphide),  which  was  a  very  important  factor  in  this 
process,  could  not,  under  the  great  pressure  due  to  great 
depth,  make  its  way  from  the  solutions  in  the  fissures  into  the 
country-rock. 

The  later  silver-lead  veins  are,  on  the  whole,  richer  in  silver  than 
the  older  ones.  This  may  be  connected  with  the  fact,  inferred  on 
physico-chemical  grounds  by  Van  Hise,  that  at  great  depth  lead 
sulphide  separates  in  larger  proportion  than  silver-sulphide  or 
sulpho-salts.  According  to  this  view,  the  precious  silver-veins 
(carrying  relatively  little  galena  and  zinc-blende)  of  recent 
eruptive  ranges  become,  at  a  very  great  depth,  richer  in  galena 
and  zinc-blende.  This  seems  to  be  sometimes  the  case.  (In- 
stances are  given  further  on.) 

This  hypothetical  view  is  not  contradicted  by  the  fact  that 
many  of  the  older  silver-lead  veins,  as  at  Andreasberg  and 
Kongsberg,  are  highly  "  precious " — i.e.,  relatively  poor  in 
galena  and  zinc-blende;  for  this  character  may  be  due  to  the 
small  proportion  of  lead  and  zinc  in  the  original  vein-solutions. 

In  view  of  the  range  below  the  original  surface  through  which 
mining  is  carried  on,  beginning,  not  at  that  surface,  but  already 
thousands  of  meters  below  it,  we  may*  easily  see  that,  in  many 


PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS.  673 

districts,  the  directly  observable  differences  in  original  depth 
have  little  significance.  For  instance,  at  Kongsberg  there  is 
no  difference  in  the  character  of  the  veins  from  the  present 
surface  to  0.5-0.75  kilom.  below  it. 

In  other  districts,  however,  very  important  differences  of 
original  depth  have  been  established.  For  instance,  these  dif- 
ferences were  very  distinct  in  many  Cornish  mines,  where  the 
veins  carried :  (1)  at  the  uppermost  level  (in  the  tin-bearing 
gossan)  tin-stone  and  a  little  copper-ore  (the  latter  as  the  result 
of  a  secondary  process,  the  original  sulphides  having  been 
mostly  leached  out  of  the  gossan) ;  (2)  their  copper-ore,  with 
some  tin-stone  (in  the  Dolcoath  mine,  to  the  depth  of  0.3 
to  0.33  kilom.  below  the  present  surface);  (3)  still  deeper, 
first,  a  zone  of  mixed  tin-stone  and  copper-ore,  and  under  that 
almost  exclusively  tin-stone.  The  veins  traverse,  in  depth, 
chiefly  granite;  at  higher  levels,  slates.  But  zones  2  and  3 
are  not  confined  to  either  rock.  In  this  case,  then,  the  tin- 
stone was  originally  deposited  at  a  greater  depth  than  the 
copper-ore. 

In  many  silver-lead-zinc  veins  there  is  an  increase  in  the 
proportion  of  zinc-blende  with  depth.  The  Clausthal  veins, 
and  many  in  Mexico  (Pachuca,  Zacatecas,  etc.)  are  instances. 
In  the  latter,  very  important  differences  in  the  depths  of  orig- 
inal deposition  are  often  observed.  (1)  Near  the  surface  are 
very  rich  silver- ores  (the  so-called  color  ados,  containing  cerus- 
site  with  chloride,  bromide  and  iodide  of  silver,  and  native 
silver),  the  richness  of  which  is  the  result  of  secondary  pro- 
cesses.* (2)  Below  these,  after  an  intermediate  zone  of  tran- 
sition, appear  for  the  first  time  the  so-called  negros  ores — galena, 
silver-glance,  silver  sulpho-salts,  etc. ;  and  (3)  in  the  deep  work- 
ings, say  0.5  kilom.  below  the  present  surface,  the  so-called 
/we<70-ores,t  carrying  much  zinc-blende  and  galena,  with  a  scanty 
admixture  of  true  silver-ores.  It  is  possible  that  the  Tertiary 
Mexican  veins  have  in  depth  a  character  resembling  that  of  the 
older  rather  than  that  of  the  younger  group  described  in  a  pre- 
vious part  of  this  paper. 

*  According  to  the  Mexican  geologists  and  miners  at  the  Paris  Exposition  of 
1900,  these  ores  extend,  as  a  rule,  very  little  below  the  ground -water  level. 

t  That  is,  "fire  "-ores,  or,  in  other  words,  smelting-ores.  The  surface-ores  are 
treated  by  amalgamation. 


674  PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS. 

With  regard  to  the  increase  of  zinc-blende  in  depth,  which 
has  been  observed  in  many  places,  I  have  already  observed 
that  Van  Hise,  in  his  last  paper,  concludes  upon  theoretical 
grounds  that  from  an  ascending  solution  containing  zinc  and 
lead,  the  zinc  sulphide  would  be  deposited  lower  down  than 
the  lead  sulphide.  In  many  veins  carrying  copper  and  iron 
sulphides,  the  richest  copper-ores  are  found  at  the  higher  levels. 
As  Emmons  and  Weed  have  shown  for  the  Butte  district,  this 
is  in  numerous  cases  the  result  of  a  secondary  process.  In 
sundry  localities,  however,  the  influence  of  original  differences 
of  depth  may  be  recognized.  This  is  the  case,  for  instance,  at 
Vigsnas  in  Norway,  where  the  ore,  a  fine-grained  mixture  of 
chalcopyrite  with  pyrite,  occurs  in  several  (about  seven)  nearly 
vertical  "  stocks."  In  the  upper  levels  the  pyritic  mixture 
carried  easily  3  to  4  per  cent,  of  copper;  at  the  depth  of  735 
meters  the  thickness  of  the  mass  was,  on  the  whole,  tolerably 
well  maintained ;  but  the  copper-content  had  sunk  to  about  1 
per  cent.,  or  a  trifle  more. 

A  corresponding  phenomenon  is  not  presented,  however,  by 
the  flat-lying  pyritic  masses  or  "  lineals  "  at  Roros,  which  dip 
respectively  9°,  9°  and  15°,  and  have  been  worked  in  these  dips 
to  distances  of  1080,  1350  and  about  2000  meters. 

In  the  pyritic  deposit  at  Huelva  (at  Bio  Tinto,  Tharsis,  etc.) 
the  secondary  concentration  in  the  "  zone  of  enrichment," 
immediately  below  the  "  iron  hat,"  plays  a  very  important 
part;  but  there  appears  to  be,  besides,  a  primary  distribution 
according  to  which  the  copper  diminishes  as  depth  increases.* 

According  to  many  American  reports,  there  are  also  in  the 
United  States  and  in  Chile  many  known  instances  of  the  depo- 
sition, from  an  ascending  ore-solution,  of  pyrite  and  chalcopy- 
rite, in  which  the  former  was,  to  a  considerable  extent,  de- 
posited deeper  than  the  latter. 

Not  only  in  the  sulphide-ore  deposits,  but  also  in  those  of 
iron  and  manganese  oxides,  primary  differences  of  depth  are 
recognized.  Thus  at  Romaneche  in  the  Department  of  Saone 
et  Loire,  France,  the  ore-deposits,  occurring  in  granite,  consist 
of  psilomelane  (named  romanechite  by  Lacroix,  on  account 
of  its  constant  considerable  percentage  of  baryta)  and  specular 

*  See  Zeitschr.  f.  prakt.  GeoL,  No.  7,  1899. 


PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS.  675 

hematite,  with  quartz  and  heavy  spar,  a  very  little  fluor-spar, 
and  traces  of  calcite.  The  mine  is,  with  one  exception,  the 
largest  producer  of  manganese-ore  in  France.  For  our  present 
purpose,  the  interesting  feature  is  the  change  of  proportion,  at 
different  levels,  between  psilomelane  and  hematite.  Above,  the 
psilomelane  predominates;  going  down,  the  proportion  of 
hematite  increases  with  considerable  regularity.  During  a 
visit  which  I  made  in  the  summer  of  1900,  together  with  my 
friend  and  colleague,  Prof.  L.  de  Launay,  Mr.  L.  Chamussy, 
the  director  of  the  mine,  called  our  attention  to  the  fact  that 
this  relative  increase  of  iron-ore  in  depth  is  found  in  many 
manganese-deposits.  His  explanation  was,  that  the  solution 
containing  manganese  and  iron  compounds  came  from  below, 
and  the  ores  were  precipitated  mainly  through  oxidation  by  the 
oxygen  of  the  air  contained  in  surface-waters ;  that  iron  thus 
oxidizes  more  easily  (i.e.,  sooner)  than  manganese,*  and  there- 
fore, on  the  whole,  the  larger  proportion  of  iron-ore  would  be 
deposited  lower  than  the  manganese.  This  seems  to  me  quite 
plausible,  f 

Secondary  Alterations  of  Ore-Deposits. 

Concerning  the  secondary  alterations  more  or  less  directly 
connected  with  surface  agencies,  I  would  observe,  first,  that 
such  phenomena  have  very  little  importance  in  the  Norwegian 
and  Swedish  deposits,  which  are  generally  found  in  very  solid 
rocks,  such  as  gabbro,  gneiss,  granulite,  mica-slate,  phyllite, 
etc.  The  occurrrences  of  magnetite,  specular  hematite  and 
ilmenite  show,  as  a  rule,  no  trace  whatever  of  a  zone  of  weather- 
ing— except  that  here  and  there  apatite  has  been,  to  a  slight 
extent,  leached  out.  The  dense,  massive  magnetite  resists 


#  That  from  a  solution  containing  protoxides  of  iron  and  manganese  (e.g.,  in 
carbonic-acid  water)  iron  is  precipitated  by  oxidation  before  manganese  has  long 
been  known.  The  literature  of  the  subject  is  given  in  my  work  "  Salten  ogRanen" 
(1890-91),  in  which  a  geological  application  of  this  order  of  precipitation  was 
attempted.  See  also  Zeitschr.  f.  prakt.  Geol.,  1894,  p.  33,  and  1895,  p.  39;  also 
"The  Chemical  Kelation  of  Iron  and  Manganese  in  Sedimentary  Kocks,"  by  K. 
A.  F.  Penrose,  Jour,  of  Geol,  1893,  vol.  i.,  p.  356. 

f  I  regret  that  this  contribution  must  be  prepared  for  publication  in  such  haste 
that  I  have  not  time  to  obtain  by  correspondence  further  details  concerning  this 
primary  difference  of  distribution  in  the  manganese-deposits.  Nevertheless,  I 
venture  to  give  here  the  above  theoretical  explanation. 

43 


676  PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS. 

even  denudation,  so  that,  for  instance,  the  extraordinarily  large 
deposit  at  Efrunawara-Luossawara,  in  northern  Sweden,  forms 
a  real  "iron  mountain,"  rising  about  100  meters  above  the 
surrounding  rocks.  The  same  is  true  of  the  Taberg,  a  moun- 
tain of  titanomagnetite-olivinite,  in  southern  Sweden.  Even 
the  pyritic  deposits,  like  Roros,  Sulitelma,  Vigsnas,  etc.,  and 
the  nickel-pyrrhotite  deposits,  like  Erteli,  5  to  10  meters  in 
thickness,  show  a  zone  of  weathering  seldom  more  than  one  or 
two  meters  deep.  At  Fahlun,  where  the  pyritic  mass  was  very 
wide,  the  "  iron  hat "  was  probably  deeper. 

This  insignificance  of  the  secondary  alterations,  even  in  the 
pyritic  deposits,  is  probably  due  to  two  chief  causes:  (1)  that 
the  surface  was  polished  clean  by  the  Quaternary  ice-sheet; 
and  (2)  that  the  solidity  of  the  country-rocks  has  permitted 
very  little  circulation  of  water.* 

In  sharp  contrast  stand  the  thick  pyritic  deposits  of  Rio 
Tinto,  etc.,  in  the  Huelva  district,  where  the  "iron  hat"  ex- 
tends to  35-50  meters.  Here  the  Quaternary  ice-period  was 
lacking,  and  the  country-rocks  were  much  more  porous  than  in 
the  corresponding  Scandinavian  formations.  Concerning  these 
secondary  alterations,  I  would  refer  to  an  earlier  work  of  my 
own,  which  is  mentioned,  among  others,  in  the  papers  of  Messrs. 
Emmons  and  "Weed. "  Especially  noteworthy  here  is  the  re- 
formation of  rich  sulphides  in  the  "  zone  of  enrichment,"  and 
the  very  characteristic  re-formation  in  Mass  II.,  at  Rio  Tinto, 
of  a  narrow  zone,  rich  in  gold  and  silver,  on  the  boundary  be- 
tween the  "  iron  hat "  and  the  underlying  pyritic  mass. 

Concerning  the  chemistry  of  the  secondary  alteration  of  ore- 
deposits  I  can  add  little,  in  this  hasty  review  of  the  subject,  to 
the  excellent  discussions  of  Don,  Emmons,  De  Launay,  Pen- 
rose,  Van  Hise,  Weed  and  others,  f  Especially  interesting  are 

*  I  know  several  deep  mines  in  Norway,  in  which  the  lowest  pump-station  is 
only  about  250  meters  from  the  surface.  In  one  of  them,  water  for  use  in  drilling 
below  that  level  has  to  be  carried  down. 

f  I  will  only  introduce  some  observations  upon  the  solvent  effect  of  the  ferric 
salts,  Fe2(SO4)3  and  FeCl3,  upon  sulphide  ores.  To  test  this  point,  I  made  in 
November,  1896,  the  following  experiment  : 

Samples  of  6  grammes  each  of  pulverized  chalcocite,  bornite,  chalcopyrite, 
pyrrhotite  and  pyrite  were  separately  treated  in  Erlenmeyer  jars,  100  cub.  cm.  of 
neutral  aqueous  solution  containing  30  grammes  of  FeCl3  being  poured  upon 
ea  h  sample,  after  which  they  were  allowed  to  stand  quietly  at  the  ordinary 


PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS.  677 

the  proofs  furnished  of  late  years  from  North  America  that 
secondary  alteration  often  extends  far  below  the  ground-water 
level  and  the  re-formation  of  sulphides  in  the  zone  of  enrich- 
ment, investigated  especially  by  Emmons  and  Weed. 

I  would  here  refer  to  the  collection  of  specimens  from  the 
gold-district  of  West  Australia  which  was  exhibited  last  year 
at  Paris  under  the  direction  of  Mr.  A.  G.  Holroyd.  That  the 
gold  of  many  localities  had  been  first  dissolved,  most  probably' 
in  Fe2(S04)3,  and  afterwards  precipitated,  could  be  clearly  seen 
in  a  whole  series  of  specimens. 

1.  From  the  zone  of  weathering  in  many  veins  were  shown 
small  and  exquisitely  beautiful  crystals  of  gold,  sitting  upon 

house-temperature  of  about  14°  C.  After  a  few  weeks  the  chalcocite  was  almost 
entirely  dissolved,  and  the  bornite  had  been  very  strongly  attacked.  On  the  other 
hand,  at  the  end  of  nine  months  the  chalcopyrite  was  affected  but  slightly,  the 
pyrrhotite  a  little  more,  and  the  pyrite  not  at  all. 

At  the  present  time,  after  the  lapse  of  4  years  and  1  month,  the  chalcocite  and 
bornite  have  long  been  completely  dissolved  ;  the  pyrrhotite  is  almost  all  dis- 
solved ;  the  chalcopyrite  has  been  somewhat  further  affected  (by  far  not  so  much 
as  the  pyrrhotite),  and  the  pyrite  has  been  attacked,  though  very  slightly.  From 
the  first  lour,  and  probably  also  to  a  small  extent  from  the  pyrite,  sulphur  has 
separated.  The  filtrates  from  the  chalcocite  and  bornite  showed  with  BaCl2  a 
weak  trace  of  H2SO4  ;  that  of  the  chalcopyrite  a  somewhat  stronger  trace ;  and 
that  of  the  pyrite  a  trace  stronger  still,  yet,  after  all,  amounting  to  little.  The 
formula  is : 

Cu2S  +  4FeCl3  =  2CuCl2  -f  4FeCl2  -f-  S,  or  Cu2S  +  2Fe2(SO4)3  =  2CuSO4+  4FeSO4 

+a 

Weed  gives  the  formula  thus  :  . 

Cu2S  -f-  5Fe2(SO4)3  +  4H2O  =  2CuSO4  +  10FeSO4  +  4H2SO4. 

In  the  reactions  with  Cu2S  and  CuS,  however,  the  sulphur  does  not  appear  to 
be  oxidized  to  sulphuric  acid,  though  this  occurs  in  subordinate  degree  in  the 
reactions  with  FeS  and  FeS2. 

The  above  experiments  were  made,  as  stated,  at  ordinary  house-temperatures. 
At  higher  temperatures  the  process  is  very  much  more  rapid.  I  was  present  in 
1893  at  an  experiment  in  the  Siemens-Halske  metallurgical  testing-laboratory  at 
Berlin,  when  pulverized  unroasted  pyrites  from  Rio  Tinto,  containing  3  per  cent, 
of  copper  and  nearly  50  per  cent,  of  sulphur,  was  stirred  in  a  weakly-acid  solution 
of  ferric  sulphate  (50  grammes  of  iron  to  the  liter),  at  80°-90°  C.  After  6  hours, 
the  percentage  of  copper  had  been  reduced  to  0.4.  Zinc-blende  is  also  attacked, 
though  not  as  strongly  as  chalcopyrite.  These  reactions  are  metallurgically 
utilized  in  the  Siemens-Halske  electrolysis  of  copper-ores,  and  in  the  present 
leaching  of  pyrites  at  San  Domingo,  Tharsis,  etc.,  in  the  Huelva  district. 

Metallic  silver  also  is  very  rapidly  attacked  by  Fe2(SO4)3.  Gold  will  be  considered 
below. 

Pyrite  is  one  of  the  commonest  minerals  in  sulphide-deposits ;  its  weathering 
yields  Fe2(SO4)3,  which  plays  an  exceedingly  important  part  in  the  secondary 
alteration  of  ore-deposits,  as  I  have  shown  in  earlier  publications. 


678  PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS. 

cobalt-manganese-ore  (asbolite),  which  is  unquestionably  a  sec- 
ondary mineral,  yet  older  than  the  gold  which  has  been  pre- 
cipitated upon  it. 

2.  In  many  samples  from  gravels  or  placers,  gold  could  be 
seen  in  small  breaks  in  iron-ocher,  limonite,  etc. 

3.  Gold  appeared  also  in  stalactites,  or  "  drip-stones,"  con- 
sisting chiefly  of  iron-ocher  and  calcite.     In  this  case  the  gold 
was  unquestionably  in  a  ferric  solution. 

4.  Again,  gold  from  various  localities  was  seen  as  a  very 
thin  tarnish,  "  breathed,"  as  it  were,  upon  the  pebbles  of  the 
placer-conglomerates. 

5.  Several  tree-roots  were  exhibited,  upon  which  gold  was 
sitting.*      Here  the  gold  had  been  reduced  or   precipitated 
from  solution  by  organic  substances. 

6.  Finally,  gold  was  to  be  seen,  in  several   cases,  in  fine 
cracks  in  the   dried  clay  of  the  placers,  into  which  it  had 
percolated  while  dissolved,  to  be  precipitated  as  a  thin  coating 
upon  the  clay. 

I  am  aware  that  series  of  similar  instances  have  been  de- 
scribed already  from  America,  Australia  and  South  Africa; 
but  I  have  dwelt  upon  these  new  exhibits  from  West  Australia 
because  they  plainly  show  that  the  solubility  of  gold  may  play 
a  quantitatively  important  part.f 

The  same  collection  showed  beautifully  the  weathering  of  the 
telluric  gold-veins  of  Kalgoorlie.  The  mines,  as  is  well 
known,  carry  in  depth  (down  to  1150  feet,  in  the  year  1900) 
very  rich  gold-tellurides  (calaverite,  sylvanite,  kalgoorlite,  pet- 
zite),  sometimes  in  masses  of  extraordinary  weight  (50-100 
kilog).J  In  the  neighborhood  of  these,  the  ordinary  phe- 
nomena of  flake-,  sheet-  and  wire-gold  are  often  found,  the 
native  gold  being  sometimes  intergrown  with  the  telluride 
mass,  and  sometimes  independent  of  it.  In  the  highly  oxi- 

*  The  label  read  :  "  Great  Boulder  Main  Keef.  Boot  of  tree,  found  at  70-ft. 
level.  Two  pieces  of  wood,  with  gold-deposition.  ( Very  rare. )  W.  A." 

f  The  platinum  metals,  on  the  contrary,  are  to  be  regarded  as  practically 
insoluble  by  the  chemical  reagents  encountered  in  nature.  See  note  on  p.  131. 

J  I  will  not  enter  here  upon  the  discussion  of  so  many  years'  standing  con- 
cerning the  "mechanical"  vs.  the  "  chemical"  origin  of  gold -nuggets  in  placers. 
(Notwithstanding  the  solubility  of  gold,  I  adhere  to  the  "  mechanical"  explana- 
tion.) But  I  may  say,  in  passing,  that  in  West  Australia  the  masses  of  gold- 
tellurium  found  in  the  veins  are  as  large  as  the  placer-nuggets  of  other  regions. 


PROBLEMS    IN    THE    GEOLOGY    OF    ORE-DEPOSITS.  679 

dized  upper  vein-zones,  the  gold-tellurides  have  been  entirely 
decomposed,  metallic  gold  and  derivative  compounds  of  tellu- 
rium being  formed,*  and  this  metallic  gold,  appropriately 
called  "  sponge-gold,"  "  mustard-gold,"  etc.,  could  be  easily  dis- 
tinguished by  its  peculiar  structure  from  the  native  gold  occur- 
ring in  depth.  This  is  an  indication  that  the  deep  native  gold 
is  not  a  secondary  formation  from  gold-telluride,  but  a  primary 
metallic  precipitate.  Secondary  alteration  thus  helps  us  to 
decide  a  question  which  has  been  discussed  for  many  years, 
especially  in  Austria-Hungary,  where  each  of  the  views  just 
stated  has  been  held  by  many  observers. f 

It  is  well  known  that  in  numerous  ore-deposits,  all  over  the 
world,  unusually  rich  ore-bodies  have  been  formed  by  second- 
ary processes  more  or  less  directly  connected  with  the  surface. 
"We  need  mention  only  Pachuca  and  Zacatecas,  in  Mexico; 
Pasco,  in  Peru ;  Potosi  and  Oruro,  in  Bolivia ;  Chanarcillo, J 
in  Chile;  Broken  Hill,  in  Australia;  Mednorudjansk,  in  the 
Ural,  etc.  Our  knowledge  of  the  secondary  formation  of  very 
rich  bonanzas  is  now  specially  enlarged  by  the  investigations 
of  Emmons  and  Weed  on  secondary  sulphide-enrichments 
below  the  ground-water  level,  as  at  Butte,  Montana. 

Since  in  the  development  of  science  it  has  been  so  often  seen 
that  new  ideas  or  impulses  are  liable  to  be  overestimated,  I  will 
here  add  that  there  are  innumerable  rich  "  shoots,"  "  chimneys," 
"  edle  Balden,"  "  Adelsvorschiibe"  "bonanzas,"  etc.,  which  have 
nothing  to  do  with  secondary  processes,  being  of  exclusively 
primary  character,  and  dependent  upon  the  laws  which  gov- 
erned the  original  ore-deposition.  I  may  cite  as  examples 
Kongsberg,  Andreasberg,  Schemnitz,  the  rich  shoots  in  the 
Transylvanian  gold-veins,  etc.  And  my  study  of  the  literature 

*  The  same  is  known  to  be  true  of  Cripple  Creek. 

f  On  other  grounds,  I  have  formerly  expressed  my  adherence  to  the  latter 
view — namely,  the  primary  character  of  the  ordinary  native  gold  of  the  deep 
zones.  See  Zeitschr.  f.  prakt.  Geol,  1898,  p.  418  ;  1899,  pp.  179-180. 

4.  See  F.  A.  Moesta,  Ueber  das  Vorkommen  der  Chlor-,  Brom-  und  Jodveroindungen, 
u.  s.  w.,  besonders  in  Chili  (1870).  He  points  out  that  at  the  outcrop  of  the  silver- 
veins  of  Chanarcillo,  etc.,  the  relative  proportions  of  chlorine,  bromine  and  iodine 
to  one  another  are  about  the  same  as  in  sea- water,  to  the  percolation  of  which  he 
attributes  the  formation  of  these  haloids.  The  explanation  given  by  K.  A.  F. 
Penrose  (Jour,  of  Geol.,  vol.  ii.  (1894),  p.  34,  for  the  presence  of  silver-haloids  in 
the  arid  regions,  which  connect  them  with  neighboring  salt  lakes  and  marshes, 
seems  to  me  more  acceptable. 


680  PROBLEMS    IN    THE    GEOLOGY    OP    ORE-DEPOSITS. 

of  the   Comstock  lode  has  given  me  the  impression  that  its 
famous  bonanzas  were  of  primary,  not  secondary,  origin. 

The  question,  "What  is  of  primary  and  what  of  secondary 
nature  ?  will  doubtless  long  remain  an  interesting  and  often  dif- 
ficult problem  for  discussion. 

POSTSCRIPT. 

The  foregoing  contribution  is  in  many  respects  much  less 
complete  and  more  fragmentary  than  I  would  have  it.  If,  with 
some  hesitation  on  that  account,  I  have  decided  notwithstand- 
ing to  send  it  to  the  Institute,  it  is  in  the  hope  that  its  defects 
of  form  will  be  judged  in  the  light  of  the  fact  stated  in  the  in- 
troduction, that  the  manuscript  was  begun  on  the  3d  and  fin- 
ished on  the  31st  of  December. 

I  close  this  work  of  mine  on  the  last  day  of  the  nineteenth 
century,  with  a  miner's  hail,  "  Gluck  Auf !"  to  my  numerous 
American  colleagues,  unknown  to  me  personally,  yet  well 
known  through  their  scientific  labors,  and  held  in  high  esteem. 
Undoubtedly  the  new  century  will  fill  up  many  defects  and 
solve  innumerable  riddles  and  doubts  in  the  science  of  ore- 
deposits. 


THE   IGNEOUS   ROCKS   IN   THE   FORMATION    OF   VEINS.        681 


The  Role  of  the  Igneous  Rocks  in  the  Formation  of  Veins. 

BY  J.   F.    KEMP,   NEW  YORK  CITY. 
(Richmond  Meeting,  February,  1901.) 

CONTENTS. 

PAGE 

INTRODUCTION,     .        .        .        .        ...        •        ...       .        .  681 

I.  THE  COMPETENCE  OF  THE  IGNEOUS  HOCKS  TO  SUPPLY  THE  MATERI- 

ALS OF  VEINS,    .         .        .     :  .     .   ,        .        .        .        .        .-        .  683 

The  Demonstrated  Presence  of  the  Metals  in  the  Igneous  Hocks,  .        .  683 

The  Presence  of  the  Metals  in  the  Sedimentary  and  Metamorphic  Kocks,  684 

Conclusions,    .         .         .         .        '.""•'".         .         .         .        .  686 

The  Abundance  in  Igneous  Hocks  of  Vapors  or  Dissociated  Gases  which 

will  Yield  Water  on  Emission  and  Cooling,        .         ,     .  •  »  •  .     ..       .  687 

The  Sequence  of  Eruptions,  .         .         .         .         .         .         .        .         .  689 

The  Sequence  of  Vein-Formations,         .         .         .         ...         .  691 

Contact-Metamorphism,  .  .  .  .  .  .  .  .  .  692 

Pegmatites, •  „  -.:  .  ,  »  ,  .  693 

Frequency  of  Pneumatolitic  Minerals  in  Veins,.  ....  694 

Surface-Flows  of  Igneous  Eock  Unfavorable  to  Vein-Formation,  .  .  695 

II.  THE  GROUNDWATER,  ^  .        i        .        .        .        .        .        .        .         .  695 

The  Common  Conception  of  the  Ground  water,       .         .         ...  695 

Experience  in  Deep  Mines  and  Wells,    .         ,        .        .        .        ...  696 

Artesian  Basins,      .         .         .         .  .         .         .         .         .         .  702 

Hot  Springs, .        .        .  '      .         .  703 

The  Irregular  Distribution  of  the  Groundwater  near  the  Surface,  .         .  706 

III.  THE  DISTRIBUTION  OF  MINING  DISTRICTS,    .        .        .        .        ...  707 

KESUME, 708 

INTRODUCTION. 

THE  saying  that  "  of  all  the  known  regions  of  the  universe, 
the  most  unsafe  to  reason  about  is  that  which  is  under  our 
feet/'*  might  well  be  the  motto  of  the  present  paper,  in  view 
of  the  writer's  profound  appreciation  of  the  difficulties  and  un- 
certainties of  the  subject.  In  such  a  field,  the  temptation  is 
very  strong  to  announce  a  probable  proposition,  and  then  to 
defend  it  with  a  loyalty  insensibly  graduating  into  partisanship. 
Conscious  of  this  danger,  the  writer  has  endeavored  to  main- 
tain an  impartial  and  candid  form  of  statement,  though  others 
may  feel  that  he  has  not  been  wholly  successful. 

The  subject,  as  here  considered,  falls  naturally  into  two  di- 

*  Fisher's  Physics  of  the  Earth's  Crust,  p.  89. 


682    THE  IGNEOUS  HOCKS  IN  THE  FORMATION  OF  VEINS. 

visions.  In  the  first,  the  competence  of  igneous  magmas  to 
supply  both  the  contents  of  veins  and  the  solutions  which  are 
the  common  carriers  of  the  minerals  is  set  forth.  In  the  second, 
the  phenomena  and  the  more  or  less  current  conceptions  of  the 
groundwater  are  taken  up. 

This  paper  is  limited  to  "  veins,"  as  the  term  is  ordinarily 
understood.  It  practically  excludes  the  common  deposits  of 
those  metals  which  appear  in  appreciable  percentages  in  F.  W. 
Clarke's  latest  estimated  composition  of  the  earth,*  namely, 
Al,  8.16;  Fe,  4.64;  Ti,  0.41;  Mn,  0.07;  Or,  0.01;  M,  0.01. 
Of  these,  iron  and  manganese  are  admittedly  favorable  subjects 
for  circulating  meteoric  waters,  which  are  conceded  to  be  of 
themselves  effective  in  the  outer  1000  to  2000  ft.  of  the  thick- 
ness of  the  earth's  crust.  It  is  one  thing,  for  example,  that  de- 
posits of  iron-ore  in  the  Lake  Superior  region  should  result 
from  the  rearrangements  of  iron  and  silica  in  a  rock  which  con- 
tains 15  to  25  per  cent,  of  the  former,  and  quite  a  different 
thing  for  the  less  common  metals,  and  above  all  the  precious 
metals,  to  be  concentrated  in  veins  from  what  we  have  reason 
to  believe  is  a  condition  of  excessively  sparse  dissemination  in 
compact  rocks.  Experience  gained  with  the  former  conditions 
should  not  be  unduly  influential  in  the  study  of  the  latter. 

Of  the  commoner  metals  cited  above,  iron  (with  titanium), 
chromium,  nickel  and  perhaps  aluminum  are  at  times  abun- 
dant enough  in  the  original  minerals  of  igneous  rocks  to  con- 
stitute ores. 

It  may  be  interesting  and  valuable  as  an  aid  in  establishing 
a  correct  perspective  to  note  the  relative  proportions  of  the  or- 
dinary metals  in  the  product  of  the  United  States  for  1898, 
the  latest  year  for  which  statistics  have  been  furnished  by  the 
U.  S.  Geological  Survey.  Reducing  the  weights  to  grammes, 
and  taking  the  weight  of  the  gold-product  as  unity,  the  ratios 
are  found  to  be  as  follows :  Iron,  120,950;  copper,  2487;  lead, 
2098;  zinc,  1090;  aluminum,  26;  silver,  22;  quicksilver,  11. 
This  calculation  would  be  more  significant  if  it  covered  the 
product  of  the  world ;  but  the  necessary  data  are  not  available. 
It  affords,  however,  within  limits,  a  certain  conception  of  the 
relative  abundance  of  the  several  metals. 

*  Bulletin  of  the  U.  S.  Geological  Sumey,  No.  168,  p.  15. 


THE    IGNEOUS    ROCKS    IN    THE    FORMATION    OF  VEINS.          683 

I.  THE  COMPETENCE  OF  THE  IGNEOUS  ROCKS  TO  SUPPLY  THE 
MATERIALS  OF  VEINS. 

The  Demonstrated  Presence  of  the  Metals  in  the  Igneous  Rocks. 

Within  recent  years  many  assays  of  rocks  have  been  made, 
in  order  to  throw  some  light  on  the  source  of  the  metals  in 
ores.  In  selecting  the  samples  for  analysis,  certain  precautions 
are  essential.  Fresh  rock  must  be  taken ;  and  the  possible  im- 
pregnation with  small  amounts  of  infiltrated  metals  must  be 
avoided,  or  else  the  significance  of  the  results  will  be  vitiated. 
The  amounts  to  be  measured  are  excessively  small,  and  their 
determination  taxes  the  resources  of  the  chemist  to  the  utmost. 
For  example,  one  ounce  to  the  ton  means  ^  of  1  per  cent. ; 
and  in  some  dry  assays  even  fractions  of  a  grain — there  being 
480  grains  to  the  ounce — are  determined.  Reagents  (particu- 
larly the  litharge  used  in  dry  assays  for  gold  and  silver)  must 
be  pure  to  the  last  degree. 

All  these  precautions  have  been  observed,  however,  in  a 
large  number  of  cases;  and  a  very  considerable  amount  of 
trustworthy  data  has  been  accumulated,  going  to  show  that  the 
common  metals  are  certainly  present  in  igneous  rocks,  and  that 
one  or  another  of  them  is  contained  in  nearly  all  the  commoner 
igneous  types  (acid,  intermediate  and  basic).  Some  metals 
seem  to  favor  one  rock  and  some  another — a  feature  which  has 
been  treated  at  some  length  by  De  Launay*  and  Yogt,f  and 
more  briefly  summarized  by  the  writer.  J  It  has  been  shown 
also  that  the  ferro-magnesian  silicates  are  richer  in  the  metals 
than  is  the  rock  as  a  whole,  and  that  they  are  probable  sources 
of  the  metals.  The  metals  appear  in  them  either  as  bases  or 
as  metallic  inclusions. 

It  was  the  original  purpose  of  the  writer  to  tabulate  these 
results  ;  but  the  mass  of  data  was  found  to  be  too  large  to  be 
practicably  handled  in  this  way,  and  therefore  only  the  above 
general  statements  are  made.  Many  references,  however,  are 
given  in  the  work  last  cited. 

We  must  bear  in  mind  that  the  results  of  these  assays  and 

*  L.  De  Launay,  Annales  des  Mines,  August,  1897.     Reprint,  p  45. 
t  J.  H.  L.  Vogt,  Zeitsch.  fur  prakt.  Geologic,  vi.,  225  (1898). 
J  J.  F.  Kemp,   Ore-Deposits  of  the  United  States  and  Canada.     Third  edition 
(1900),  p.  35. 


684         THE    IGNEOUS    ROCKS    IN    THE    FORMATION    OF  VEINS. 

analyses  have,  to  a  large  extent,  but  general  interest  and  ap- 
plication. Only  from  the  point  of  view  of  a  lateral-secretionist 
of  the  Sandberger  type  does  it  follow  that  the  ores  in  a  vein 
have  been  derived  from  the  wall-rocks  which  are  accessible  for 
assay.  In  instances  like  Butte,  Mont.,  in  which  two  sets  of 
veins,  of  greatly  contrasted  mineral  contents,  are  found  in  the 
same  country-rock,  other  sources  must  be  assumed  for  at  least 
one  series  of  them,  no  matter  what  are  the  theoretical  predilec- 
tions of  the  observer.  Nevertheless,  it  is  a  fact  of  the  greatest 
importance  that  the  presence  of  the  metals  in  igneous  rocks 
has  been  established.  Not  all  igneous  rocks  have  yielded  such 
results  on  assay.  The  general  experience  has  been  that  when 
samples  of  several  varieties  have  been  collected  in  a  given  dis- 
trict, some  have  proved  barren;  and  it  must  be  admitted  that 
some  negative  results  have  been  obtained.  As  a  rule,  however, 
they  are  decidedly  fewer  than  the  positive  results.  It  is  like- 
wise true  that  not  all  igneous  districts  contain  veins  of  ore. 
Great  areas  of  surface-flows,  such  as  the  basalt  plains  of  Idaho, 
Oregon  and  Washington,  are  notably  barren,  probably  for  rea- 
sons that  will  be  subsequently  advanced. 

The  elements  of  the  minerals  which  form  the  common  varie- 
ties of  gangue  are  found  in  all  the  igneous  rocks,  and  in  the 
sedimentary  rocks  as  well.  Quartz  is  much  the  commonest  of 
the  gangue-minerals,  and  silica  is  universally  present  in  the 
rocks.  Calcite  and  fluorite  may  derive  their  calcium  -from  an 
equally  wide  range  of  rocks  and  minerals.  Barium  and  stron- 
tium are  "understudies"  of  calcium,  and  available  iron  for 
siderite  is  present  on  every  hand.  Where  rock,  in  a  stage  of 
greater  or  less  alteration,  forms  the  gangue,  it  has  no  special 
significance  in  this  connection ;  and  gangue-minerals  other  than 
those  cited  are  relatively  uncommon  and  unimportant. 

The  Presence  of  the  Metals  in  the  Sedimentary  and  Metamorphic 

Rocks. 

Wherever  the  metals  are  found  in  the  sedimentary  or  meta- 
morphic  rocks,  it  is  logically  necessary  to  refer  them  to  original 
sources  in  the  igneous  rocks,  from  which  they  have  been 
derived  either  by  solution  or  abrasion.*  In  the  former  case, 

*  Ore-Deposits  of  the  United  States  and  Canada.     Third  edition,  p.  32. 


THE    IGNEOUS    ROCKS    IN    THE    FORMATION    OF  VEINS.          685 

the  processes  of  introduction  are  essentially  those  to  be  sub- 
sequently discussed ;  in  the  latter,  except  in  the  case  of  placers 
(which  are  negligible,  in  this  connection,  on  account  of  their 
small  amount),  the  distribution  of  the  metals  is  extremely 
sparse.  If  we  begin  with  a  rock  which  contains  but  hun- 
dredths  or  thousandths  of  1  per  cent,  and  imagine  it  broken 
up  by  the  processes  of  erosion,  its  minerals  subject  to  solution 
and  dispersion,  and  to  commingling  with  foreign  matter, — or, 
if  they  are  heavy,  to  concentration  in  placers, — the  resulting 
sediment  is  a  less  favorable  source  of  supply  for  migrating  solu- 
tions than  was  the  original  igneous  rock.  The  assays  and 
analyses  which  have  been  made  confirm  this  general  state- 
ment, but  they  are  hardly  as  abundant,  taking  the  world  over,  as 
are  those  which  have  been  prepared  of  the  igneous  rocks.  An 
exception  is  the  really  remarkable  work  by  J.  R.  Don*  in 
Australia. 

In  making  assays  and  analyses  of  sedimentary  and  meta- 
m orphic  rocks,  it  is  important  to  observe  the  same  precautions 
as  were  outlined  for  the  igneous  rocks;  and,  in  interpreting 
them,  secondary  impregnation  must  be  guarded  against.  The 
following  brief  summary  of  the  results  of  several  workers  will 
give  an  idea  of  the  evidence  in  hand.  Dr.  Don  has  made  and 
tabulated  a  vast  number  of  analyses  of  the  wall-rocks,  chiefly 
sedimentary,  of  the  Australian  gold-veins.  He  was  able  to 
determine  the  presence  of  gold  in  fractions  of  a  grain  per  ton 
of  rock  in  a  large  number;  but  his  tests  indicated  that  only 
those  rocks  which  also  contained  pyrites  gave  any  returns  for 
gold.f  There  is,  therefore,  the  presumption  that  the  gold  and 
pyrites  were  introduced  as  an  impregnation ;  pyrites  not  being 
a  mineral  favorable  to  sedimentation.  Mr.  Winslow,J  in  con- 
nection with  his  most  valuable  investigations  of  the  lead-  and 
zinc-deposits  of  Missouri,  engaged  Mr.  J.  D.  Robertson  to  pre- 
pare a  series  of  analyses  of  the  rocks  of  Missouri,  both  sedi- 
mentary and  igneous,  for  lead  and  zinc.  The  samples  were 
taken  in,  near  and  remote  from  mines,  and  in  not  a  few  cases 

*  Trans.,  xxvii.,  564. 

t  It  may  be  again  remarked  that  a  grain  is  -^-^  of  an  ounce,  and  that  these 
values  were  therefore  thousandths  and  tens  of  thousandths  of  an  ounce  per  ton. 
If  one  thirty-thousandth  of  this  remote  decimal  is  then  calculated,  the  values  in 
true  decimals  will  Le  given.  They  are  almost  inconceivably  small. 

%  Arthur  Winslow.     Geol.  Surv.  of  Mo.,  vol.  vii.,  p.  479. 


686         THE    IGNEOUS    ROCKS    IN    THE    FORMATION    OF  VEINS. 

amounts  were  found  equal  to  several  thousandths  of  one  per 
cent.  When,  however,  we  compare  the  analyses  of  the  sedi- 
ments with  those  of  the  igneous  rocks,  we  find  that  the  latter, 
as  a  rule,  are  by  one  place  of  decimals  richer  than  the  former, 
and  to  that  extent  are,  generally  speaking,  more  favorable 
sources  of  the  metals.  These  results  justify  the  statement 
made  above  that  erosion  and  sedimentation  tend  to  disperse 
the  original  metallic  contents  of  the  igneous  rocks,  and  to 
place  them  in  conditions  less  favorable  for  concentration  by 
solution. 

With  regard  to  the  metamorphic  rocks  especially,  it  may  be 
said  that  increasing  experience  and  more  accurate  knowledge 
have  tended  to  prove  the  presence  among  them  of  crushed  and 
sheared  igneous  types,  whose  foliation  is  of  mechanical  origin. 
Considered  as  favorable  sources  of  the  metals,  the  same  re- 
marks would  apply  to  them  as  those  already  made  regarding 
the  unaltered  igneous  rocks.  A  good  illustration  is  the  gold- 
belt  of  the  Southern  States,  which  is  now  recognized  to  em- 
brace amid  its  schistose  types  a  very  large  proportion  which 
are  of  this  original  character. 

Conclusions. — Sedimentary  rocks  are  far  less  favorable  sources 
of  the  metals  than  are  igneous ;  but  the  statement  must  not  be 
interpreted  as  a  law,  though  preponderating  experience  justifies 
it.  Omitting  the  metals  excluded  in  the  opening  paragraphs, 
sedimentary  districts  not  associated  with  igneous  rocks  are,  as 
a  matter  of  experience,  pre-eminently  barren.  The  lead-  and 
zinc-deposits  of  the  Mississippi  valley  are  almost  the  only 
important  exceptions  which  can  be  suggested,  and  of  these 
it  is  fair  to  say  that  increasing  observation  gives  some  ground 
for  connecting  them  with  dislocations,  certainly  in  southwest 
Missouri,  and  to  a  less  degree,  perhaps,  in  southeast  Mis- 
souri, and  for  favoring  the  views  which  have  been  especially 
advocated  in  recent  years  by  W.  P.  Jenney.  The  ores  are, 
however,  confessedly  hard  problems.  Concentration  from  the 
neighboring  wall-rock  has  been  upheld  in  the  case  of  the  veins 
of  the  Upper  Mississippi,  more  especially  within  a  year  past, 
by  C.  R.  Van  Hise.*  Although  there  is  no  known  occurrence 
of  igneous  intrusions  in  the  two  regions  cited,  or  in  the  gash- 

*  "  Some  Principles  Controlling  the  Deposition  of  Ores,"   Trans.,  xxx.,  103 
(p.  77  of  pamphlet  edition)  ;  this  vol.,  pp.  282-432. 


THE   IGNEOUS   ROCKS   IN   THE    FORMATION    OF  VEINS.         687 

vein  district  of  Wisconsin,  yet  it  is  true  that  peridotites  have 
been  discovered  with  the  lean  veins  of  western  Kentucky,*  and 
rocks  of  this  type  have  elsewhere  been  found  in  regions  where  no 
eruptives  were  suspected  or  anticipated  on  the  basis  of  the  local 
geology. f  In  the  larger  lead-  and  zinc-districts,  however,  there 
is  no  reason,  based  on  observation,  for  thinking  that  such  rocks 
are  present ;  and  in  the  present  state  of  our  knowledge,  these 
districts  must  be  considered  as  exceptions  to  the  general  rule. 

The  Abundance  in  Igneous  Rocks  of  Vapors  or  Dissociated  Gases 
which  will  Yield  Water  on  Emission  and  Cooling. 

The  ordinary  analyses  of  cold  samples  of  igneous  rocks  are 
of  little  if  any  value  as  an  indication  of  the  vapors  and  gases 
which  were  present  in  the  hot,  fused  magma.  The  observer 
must  turn  to  active  volcanoes  and  streams  of  molten  lava  for 
his  evidence ;  and  from  these  we  may  judge  of  the  composition 
of  intruded  masses  of  rock  which  never  reach  the  surface. 
Practically  all  students  of  volcanic  phenomena  are  agreed  that 
steam  and  its  dissociated  representatives  in  the  molten  rock  are 
the  chief,  if  not  the  only  cause  of  eruption.  The  paper  by 
Prof.  J.  H.  L.  Vogt,  presented  at  this  meeting,!  discusses  at 
some  length  the  condition  of  water  in  the  fused  rock.  All 
observers  are  agreed  that  the  first  eruption  at  any  volcanic 
vent  must  be  caused  by  the  steam  which  is  brought  up  with 
the  lava  from  the  depths  of  the  earth ;  but  there  is  a  very  gen- 
eral disposition  to  refer  the  subsequent  outbreaks  to  meteoric 
or  oceanic  waters,  which  percolate  through  the  rocks  near  the 
vent,  and  which  in  some  way  become  involved  in  the  molten 
rock.  "When  the  pressure  produced  by  them  becomes  sufficient, 
an  eruption  occurs. 

It  is  very  generally  admitted  to  be  inconceivable  that  water 
from  any  outside  source  should  be  able  to  follow  cavities  larger 
than  capillary  size  through  solid  rock,  heated  nearly  to  fusion, 
to  and  into  molten  rock  at  a  temperature  of  over  2000°  F. 
Any  water  entering  even  the  outer  and  moderately  heated  solid 
rock  would  be  evaporated  and  driven  outward.  It  is  necessary 

*  J.  S.  Diller.  Mica-peridotite  from  Kentucky.  Amer.  Jour.  Sci.,  Oct.,  1892, 
286.  f  For  example,  at  Syracuse,  Manheim  and  Ithaca,  N.  Y. 

J  "  Problems  in  the  Geology  of  Ore-Deposits,"  Trans.,  xxxi.,  125  ;  this  vol.,  pp. 
636-680. 


688    THE  IGNEOUS  ROCKS  IN  THE  FORMATION  OP  VEINS. 

therefore  to  fall  back  on  the  capillary  conduits,  through  which 
to  introduce  into  the  magma  the  accessions  of  water.  In  order 
to  prove  the  possibility  of  this  introduction,  recourse  is  had  to 
Daubree's  famous  experiment,  which  has,  however,  been  shown 
by  Osmond  Fisher*  to  have  no  bearing  on  the  case  in  point. 
Daubreef  took  a  slab  of  sandstone,  two  c.m.  (about  0.8  in.) 
thick,  and  cemented  it  between  an  air-chamber  below,  and 
a  chamber  above  which  could  be  filled  with  water.  The  tem- 
perature of  the  lower  chamber  was  raised  until  the  air-pressure 
was  about  two  atmospheres.  The  water  from  the  upper  cham- 
ber was  drawn  down  by  capillary  attraction,  even  against  this 
pressure  of  two  atmospheres,  and  moistened  the  under  side  of 
the  slab.  It  is  evident  from  this  that  capillary  attraction  can 
draw  water  downward  against  a  pressure  •  but,  as  Fisher  acutely 
remarks,  the  capillary  force  was  effective  because  it  operated 
toward  a  free  air  space.  In  fact,  it  is  only  under  these  condi- 
tions that  the  difference  in  surface-tension,  which  is  the  real 
cause  of  capillary  movement,  appears  between  the  air  and 
water  on  the  one  side  and  the  water  and  walls  on  the  other. 
The  experiment  gives  no  ground  for  thinking  that  water  would 
move  through  the  heated  walls  confining  a  reservoir  of  molten 
rock  and  become  involved  in  the  latter.  There  is  also  some 
uncertainty  about  the  efficiency  of  capillary  force  in  rocks 
which  are  under  great  pressure.  As  I  learn  from  my  colleague, 
Professor  R.  S.  Woodward,  no  assumptions  of  its  efficiency  are 
based  on  experimental  data. 

Again,  active  volcanoes  are  known,  such  as  Cotopaxi  in 
Ecuador,  which  are  nearly  20,000  feet  above  sea-level.  They 
must  draw  on  reservoirs  below  tide,  and  yet  even  at  tide-level 
cavities  in  the  rocks,  through  which  water  might  reach  the 
magma,  will  have  become  impossible  by  reason  of  the  pressure. 

It  would  therefore  seem  necessary  to  believe  that  the  ejected 
steam  and  other  vapors  of  lavas  have  been  brought  up  with  them 
from  the  depths ;  but  it  is  only  fair  to  say  that  many  think 
otherwise,  although  apparently  without  careful  analysis  of  the 
problem.  Of  the  abundance  of  the  vapors  there  can  be  no 
question.  They  often  exceed  in  volume  the  lava  itself.  The 
question  of  their  origin  only  affects  in  a  minor  way  the  argu- 

*  Physics  of  the  Earth's  Crust,  pp.  91,  92.          f  Geologic  experimentale,  p.  236. 


THE  IGNEOUS  ROCKS  IN  THE  FORMATION  OF  VEINS.    689 

ment  to  be  subsequently  made  regarding  the  cause  of  move- 
ment of  the  groundwater. 

Beyond  question,  intruded  sheets  and  laccolites  are  provided 
with  gases  similar  in  all  respects  to  surface-flows ;  but,  in  the 
nature  of  the  case,  the  gases  are  yielded  much  more  gradually, 
and  through  longer  periods  of  time.  They  undoubtedly  continue 
to  appear  until  the  rock  is  nearly  as  cold  as  the  boiling-point 
of  water  at  the  depth  at  which  they  stand.  It  must  be  ad- 
mitted that  the  hot  vapors  and  waters  yielded  by  an  intrusion 
under  these  circumstances  are  extremely  vigorous  chemical  re- 
agents* and  are  incomparably  superior  to  the  ordinary  ground- 
water,  even  when  the  latter  exists  in  any  serious  amount  below 
1500  to  2000  ft.  It  is  also  important  to  remark  that  the  pres- 
ence of  even  a  very  small  dike  in  any  region  is  proof  of  the 
existence  of  a  relatively  very  large  reservoir  of  igneous  rock, 
at  some  point  beneath  the  surface,  and  at  unknown  but  not 
great  depth. 

The  Sequence  of  Eruptions. 

One  of  the  most  interesting  features  of  eruptive  districts  is 
the  sequence  of  the  eruptive  rocks.  One  kind  of  rock  has 
followed  another  until,  in  some  instances,  a  considerable  list  can 
be  made  up.  All  will  recall  von  Richthofen's  observations  on 
the  Pacific  coast  in  the  late  sixties,  which  led  him  to  infer  that 
eruptions  habitually  begin  with  rocks  of  medium  acidity,  pass 
then  through  a  series  with  increasing  silica  up  to  rhyolite,  and 
terminate  with  basalts.  Increasing  observation  has  shown 
many  exceptions  to  this  simple  rule ;  but  of  the  general  fact 
that  molten  rocks  are  poured  out  one  after  another  from  what 
would  appear  to  be  a  common  reservoir,  there  is  no  question; 
and  students  of  the  subject  have  been  more  and  more  disposed 
to  explain  them  by  a  breaking  up  of  some  original  parent 
magma  of  intermediate  composition  into  the  several  diverse 
products. 

This  succession  of  eruptions  holds  good  in  many  localities 
of  extensive  vein-formation.  At  Butte,  Montana,  for  example, 
a  basic  granite  was  followed  by  an  acid  granite,  and  both  by 
quartz-porphyry,  with  which  latter  the  introduction  of  the  ores 
seems  to  have  Had  some  connection.  After  the  ores  had  been 

*  Regarding  this  point,  a  very  valuable  paper  is  that  of  A.  C.  Lane,  Bulletin 
GeoL  Soc.  Amer.,  v.,  259. 


690         THE   IGNEOUS   HOCKS    IN   THE    FORMATION    OF  VEINS. 

deposited,  a  great  outbreak  of  rhyolite  took  place,  with  no 
attendant  vein-formation.  At  present  the  quartz-porphyry  is 
by  far  the  least  extensive  of  them'  all,  and  forms  but  a  few 
minor  dikes ;  yet  it  is  quite  possible  that  it  may  represent  some 
greater  intruded  mass,  far  below,  from  which  the  ores  have 
come ;  and  for  the  very  reason  that  it  is  visible  in  small  amount 
it  may  be  the  most  important  of  all  the  rocks  in  connection 
with  the  genesis  of  the  ores. 

Again,  for  example,  at  Douglass  Island,  Alaska,  albite-diorite 
(sodium-syenite)  and  gabbro  have  been  identified  by  G.  F. 
Becker  in  the  order  of  their  outbreak  through  slates;  but  it 
was  only  just  before  or  along  with  the  intrusion  of  a  small 
dike  of  analcite-basalt  that  the  ore  entered.  On  the  Comstock, 
we  find  a  considerable  variety  of  eruptives  in  sequence.  There 
is  a  decided  difference  of  interpretation  between  Mr.  Becker, 
on  the  one  side,  and  Messrs.  Hague  and  Iddings  on  the  other; 
but  if  the  latter  are  correct  in  considering  Mr.  Becker's  "  later 
diabase  "  as  the  same  as  the  "  basalt,"  which  is  the  youngest 
eruptive,  then  it  was  after  the  intrusion  of  the  "  black  dike  " 
of  diabase  or  basalt  which  is  met  in  depth,  that  the  ores  came 
in  along  a  line  of  faulting.  At  Mercur,  Utah,  a  great  stratum 
of  carboniferous  limestone  was  penetrated  by  a  sheet  of  quartz- 
porphyry,  which  itself  forked  into  two  thin  prolongations. 
Immediately  beneath  the  lower  fork  of  the  sheet  are  silver 
ores,  after  the  deposition  of  which  an  interval  ensued.  Later 
on,  gold-ores  were  deposited  beneath  the  upper  fork,  having 
been  introduced,  as  is  thought  by  J.  E.  Spurr,  through  the  in- 
fluence of  a  laccolite,  assumed  to  exist  in  depth. 

Dikes  may  not  at  first  be  evident  in  mines — as  was  the  case 
in  the  Ontario  at  Park  City,  Utah.  In  the  early  work  the  vein 
apparently  filled  a  fissure  in  quartzite,  but  in  depth  a  dike  was 
met,  which  formed  one  of  the  walls. 

Over  and  over  succeeding  eruptions  have  taken  place,  and 
then  at  some  stage  (usually  after  a  minor  intrusion,  so  far  as 
the  exposures  give  the  observer  an  indication)  the  ores  were 
introduced,  and  one  may  not  be  able  to  say  whether  they  came 
in  with  or  just  after  it.  It  is  thus  evident  that  some  eruptive 
rocks  are  unfavorable  in  themselves,  or  unfavorably  situated  in 
their  present  positions,  for  vein-formation,  and  that  one  may 
appear  later  whose  advent  is  a  signal  for  the  ores  to  enter. 


THE   IGNEOUS    KOCKS   IN   THE   FORMATION    OF  VEINS.         691 

The  Sequence  of  Vein- Formations. 

There  are  also  cases  of  successive  and  contrasted  vein-for- 
mation. More  than  fifteen  years  ago  R.  C.  Hills  recognized 
three  sets  of  veins  in  the  San  Juan  region  of  Colorado,  each 
with  different  ores;  and  the  recent  work  on  the  Telluride 
quadrangle  of  the  U.  S.  Geological  Survey  has  shown  in  detail 
many  of  the  structural  relations.*  There  are  in  this  district 
four  sets  of  fissures,  but  only  one  carries  the  ores — a  remark- 
able state  of  things  if  the  ores  are  due  to  the  universal  circu- 
lation of  the  groundwater.  In  one  instance,  the  Smuggler 
vein  is  faulted  by  the  Pandora,  a  later  vein  which  does  not 
carry  ores  sufficiently  rich  to  be  mined  profitably. 

The  district  of  Freiberg,  Saxony,  is  a  very  complex  case. 
If  we  include  with  it  some  of  the  veins  of  the  Erzgebirge  that 
lie  at  a  moderate  distance,  the  following  groups  may  be  distin- 
guished: Die  Zinnerzgdnge  ;  die  kiesige  Bleierzgdnge  ;  die  edle  Blei- 
erzgdnge  ;  and  die  edle  Quarzformation.  All  these  are  recognized 
as  genetically  connected  with  the  great  eruptions  of  granite 
and  porphyry  in  Carboniferous-Permian  times.  There  are,  in 
addition,  three  other  varieties  of  veins  which  have  usually  been 
considered  as  later,  and  even  middle  Tertiary,  viz.,  die  Kobalt- 
silbererzgdnge  ;  die  barytische  Bleierzgdnge;  and  die  Eisenmanganerz- 
formation.  They  have  been  referred  to  later  eruptions  of 
igneous  rocks.  K.  Dalmer,  however,  developsf  some  proofs 
that  the  first  and  third  date  back  before  the  late  Cretaceous, 
and  even  into  the  period  of  the  older  series.  But  the  point  of 
interest  here  is  the  connection  with  eruptive  rocks,  which  is 
emphasized  by  nearly  all  observers. 

It  is  often  assumed  in  such  cases  that  new  series  of  fractures 
have  tapped  new  sources  of  ores ;  but  the  hypothesis  is  not  to  be 
ignored  that  new  intrusions  may  have  been  responsible  for  the 
change  of  solutions — and  experience  thus  far  gained  gives  the 
latter  at  least  equal  claims  with  the  former.  Indeed,  new  series 
of  fractures  can  only  go  down  through  practically  the  same 
rocks  as  older  ones,  unless  new  material  is  brought  in  by 
igneous  intrusion ;  and  hence  the  second  hypothesis,  in  the 
absence  of  proof  to  the  contrary,  would  seem  to  have  prepon- 
derant claims  over  the  first. 

*  See  C.  W.  Purington,  18^  Ann.  Rept.  U.  S.  Geol.  Surv.,  part  iii.,  p.  745. 
f  Zeitsch.  fur  prakt.  Geologic,  Jan. ,  1896,  p.  1. 

44 


692    THE  IGNEOUS  ROCKS  IN  THE  FORMATION  OF  VEINS. 

Contact-Metamorphism. 

The  observed  facts  of  contact-metamorphism  and  the  conclu- 
sions which  have  been  drawn  from  them  have  an  important 
bearing  on  this  question.  It  is  well  known  that  some  intruded 
igneous  rocks  have  exercised  a  profound  influence  on  the  wall- 
rocks  through  which  they  have  come,  while  again  other  intru- 
sions have  produced  little  or  no  effect.  The  results  depend 
very  largely  on  the  nature  of  the  walls,  earthy  limestones  and 
argillaceous  strata  being  the  most  favorable,  and  quartzose 
sandstones  the  least  so.  Of  the  igneous  rocks,  all  kinds,  in  one 
place  or  another,  have  produced  notable  results,  but  the  acidic 
and  intermediate  are  the  most  efficient.  Abundance  of  dis- 
solved vapors  seems  to  be  the  essential  thing  for  profound  effects, 
as  relatively  dry  fusion  is  unfavorable.  The  intruded  igneous 
rock  should  also  stand  in  contact  with  the  walls  for  long  periods 
and  at  a  depth  reasonably  great  below  the  surface.  All  these 
points  are  very  much  the  same  as  those  which  have  already  been 
stated  regarding  the  igneous  rocks  as  producers  of  veins. 

A  divergence  of  views  exists  as  to  the  amount  of  material 
actually  contributed  to  the  metamorphosed  rock  by  the  igneous 
agent.  Observers  on  the  continent  of  Europe  have  considered 
the  amount  to  be  in  some  instances  large,  especially  of  soda ; 
while  from  facts  noted  at  Westmoreland,  England,  where  a 
basaltic  tuff  is  penetrated  by  granite,  a  limit  of  one-twentieth  of 
an  incn  is  set  by  Alfred  Harker  for  the  migration  of  material. 
The  changes  produced  in. contact-metamorphism  are  in  this  in- 
stance almost  entirely  those  of  rearrangement.  All  observers 
must,  however,  admit  the  general  introduction  of  fluorine, 
boron  and  steam,  because  the  distinctive  contact-minerals  are 
characteristically  provided  with  these  elements.  They  are 
therefore  described  as  miner alizers,  or  as  being  pneumatolitic  in 
their  nature.  Tourmaline,  fluorite,  fluoric  micas,  chondrodite 
and  topaz  are  illustrations  of  the  resultant  minerals;  while 
biotite,  garnet,  albite,  wollastonite,  vesuvianite  and  a  number 
of  other  silicates  are  common  associates.  If,  now,  ores  are 
found  associated  with  these  minerals  and  along  the  contacts 
with  igneous  intrusions,  and  not  extending  far  back  into  the 
wall-rocks,  the  inference  is  well-grounded  that  they  have  been 
derived  from  the  eruptive.  In  the  last  paper  of  Professor 
Vogt,  already  cited,  the  cases  of  tin-ores  and  iron-ores  to  which 


THE    IGNEOUS    ROCKS    IN   THE    FORMATION    OF  VEINS.         693 

these  views  apply  are  given  at  length ;  and  in  the  paper  of  Mr. 
Lindgren*  copper-deposits  of  similar  nature  are  cited.  Fissured 
wall-rocks  which  stand  immediately  above  laccolites  rich  in 
mineralizers  would  be  in  the  situation  most  favorable  for  these 
changes;  but  opportunities  for  observation  are  restricted  be- 
cause the  laccolite  is  only  revealed  by  their  removal.  When 
they  do  persist,  however,  and  are  thick,  the  existence  of  veins 
would  suggest  the  presence  of  the  laccolites. 

Pegmatites. 

Pegmatites  have  furnished  for  many  years  a  disputed  ques- 
tion. They  are  beyond  doubt  connected  with  great  masses  of 
intruded  rock,  more  often  with  granite  than  with  any  other, 
and  are  after-births  of  the  eruptive.  Whether  they  are  them- 
selves to  be  considered  as  true  eruptives,  or  whether  dissolved 
vapors  have  played  so  large  a  part  in  their  genesis  that  they 
are  veins  rather  than  dikes,  or  whether  some  belong  to  one  of 
these  types  and  some  to  the  other,  does  not  immediately  affect 
the  question  now  before  us — their  connection  with  eruptive 
rocks  being  the  important  point. 

Pegmatites  usually  present  the  mineralogy  of  the  granites  on 
a  very  coarse  scale,  but  they  have,  in  addition,  more  abundant 
amounts  of  the  pneumatolitic  minerals.  They  may  be  rich  in 
feldspar  and  less  rich  in  quartz,  or  they  may  be  extremely  rich 
in  quartz  with  only  subordinate  feldspar  or  other  minerals. 
The  writer  believes  that  in  some  regions  of  their  extensive  de- 
velopment all  gradations  can  be  found,  from  granitic  mixtures 
to  veins  of  pure  quartz.  The  north  shore  of  Long  Island 
Sound  is  a  case  in  point.  Pegmatites  are  abundantly  developed 
in  connection  with  granites,  and  all  grades  are  shown  up  to 
practically  pure  quartz.  The  great  quartz-vein  at  Lantern 
Hill,  Mystic,  Conn.,  is  one  of  the  largest  quartz-veins  known, 
being  apparently  1000  ft.  wide  across  the  comb-in-comb  struc- 
ture, which  is  at  times  pronounced.  I  think  it  belongs  in  the 
pegmatite  series,  and  is  only  a  huge  development  of  veins  of 
a  smaller  size  which  are  abundant  around  Narragansett  Bay 
and  elsewhere,  f  Certain  parts  of  the  Lantern  Hill  quartz  show 

*  "  The  Character  and  Genesis  of    Certain  Contact-Metamorphic  Deposits,'* 
Trans.,  xxxi.,  226  ;  also  page  716  of  this  volume. 
f  J.  F.  Kemp,  Bulletin  Geol.  Soc.  Amer..  x.,  372,  1899. 


694         THE    IGNEOUS    ROCKS    IN    THE    FORMATION    OF  VEINS. 

the  presence  of  ferruginous  minerals  and  have  yielded  on  assay 
a  few  cents  of  gold  per  ton. 

The  gold-bearing  pegmatite  of  Passagem,  Brazil,  described 
by  Hussak,*  has  been  referred  to  by  Prof.  Yogt.  In  the  Trias- 
sic  diabase  of  the  Palisades,  pegmatite  veins  richly  charged 
with  pyrite  are  not  uncommon.  Last  summer,  the  writer  spent 
several  days  at  Copper  Mountain,  on  the  Similkameen  river, 
near  Princeton,  Yale  Dist,  B.  C.,  and  found  a  great  mass  of 
gabbro,  shattered  along  a  wide  belt.  Into  the  minute  fissures 
bornite  had  been  introduced  in  some  places,  and  minute  veins 
of  pegmatite  in  others,  while  in  the  Copper  Cliff  and  Copper 
Reef  claims,  on  the  banks  of  the  river,  a  huge  pegmatite  vein 
or  dike  carried  here  and  there  large  masses  of  bornite.  The 
bornite  impressed  the  observer  as  being  as  much  an  original 
mineral  in  the  vein  as  any  of  the  other  components. 

In  view  of  the  above  facts,  which  could  indeed  be  much 
amplified,  the  following  statements  seem  to  be  justified  :  Peg- 
matites are  a  more  or  less  pronounced  pneumatolitic  result  of 
igneous  intrusion.  Pegmatites  grade  insensibly  into  quartz- 
veins.  Quartz-veins  not  visibly  associated  with  pegmatites  are 
open  to  the  same  interpretation  unless  there  is  positive  evi- 
dence to  the  contrary.  On  the  other  hand,  pegmatites,  although 
widely  developed,  are  but  rarely  provided  with  metallic  minerals 
in  notable  amounts,  and  the  same  is  true  of  the  quartz-veins 
visibly  associated  with  them.  But  it  is  also  true  that  many 
regions  of  great  development  of  pegmatite-veins  are  devoid  of 
ore-bearing  veins,  as,  for  instance,  New  England,  and  it  is  prob- 
able that  the  magmas  did  not  contain  the  necessary  metals  for 
their  production. 

Frequency  of  Pneumatolitic  Minerals  in  Veins. 

Some  of  the  common  gangue-minerals  contain  those  ele- 
ments which  are  justly  associated  with  pneumatolitic  processes. 
Of  these,  fluorite  is  the  most  important ;  and  while  it  cannot 
be  always  asserted  that  it  implies  the  neighborhood  of  eruptive 
rocks,  it  yet  creates  a  presumption  in  favor  of  their  genetic 
influence.  The  gold-ores  of  Cripple  Creek,  Colo.,  and  the 
Potsdam  ores  of  the  Black  Hills,  are  cases  in  point.  Lindgren 

*  Zeitsch.  fur  prakt.  Geologic,  October,  1898,  p.  345. 


THE    IGNEOUS    ROCKS    IN    THE    FORMATION    OF  VEINS.          695 

has  already  emphasized  this  connection  in  his  extremely  valua- 
ble paper  on  "Metasomatic  Processes  in  Fissure-Veins";*  and 
therefore  it  is  only  cited  here  in  a  brief  way. 

Surface-Flows  of  Igneous  Rock  Unfavorable  to  Vein-Formation. 

The  vapors  contained  in  surface-flows  of  igneous  rock  pass 
off  directly  into  the  atmosphere,  and  therefore  do  no  geologic 
work  of  this  character.  The  most  that  could  be  expected  of 
them  would  be  small  incrustations  in  the  cracks  in  their  upper 
and  first  chilled  portions,  such  as  the  copper-minerals  and 
specular  hematite  found  in  the  crevices  of  Yesuvian  lavas. 
The  absence  of  ore-deposits  in  flows  of  this  character  argues 
nothing  against  the  efficiency  of  other  forms  of  igneous  rocks. 

II.  THE  GROUNDWATER. 

The  Common  Conception  of  the  Groundwater. 
The  general  conception  of  the  groundwater,  that  has  been 
hitherto  held,  has  involved  the  existence  of  a  standing  body, 
quite  universally  present,  and  at  a  fairly  definite  depth  below 
the  surface,  which  depth  is  characteristic  of  the  particular  dis- 
trict. The  upper  surface  is  thought  to  be  sharply  marked  and 
to  be  revealed  by  the  boundary  between  the  oxidized  or  en- 
riched ores  and  the  unaltered  sulphides  in  an  ore-body.  The 
supply  of  water  is  kept  up  by  the  contribution  of  that  portion 
of  the  rainfall  which  neither  runs  off  nor  immediately  evapo- 
rates, but  which  sinks  into  the  ground,  feeds  wells  and  springs, 
and  necessitates  pumping  in  mines.  Rocks  being  more  or  less 
porous  and  crossed  by  faults,  joints  and  cracks,  it  has  been  in- 
ferred that  the  waters  continually  migrate  downward,  partly  by 
capillary  attraction,  partly  through  small  crevices  and  partly 
through  large  ones,  until,  meeting  the  hotter  interior  zones  of 
the  earth,  they  are  forced  by  the  head  of  the  descending  cur- 
rents (that  is  by  gravitative  stress),  reinforced  by  the  loss  of 
density  due  to  accessions  of  heat,  to  rise  again  to  the  upper 
world.  During  their  journeys  they  move  laterally  as  well  as 
downward,  pass  through  vast  masses  of  rock,  relieve  them  of 
their  mineral  and  metallic  contents,  and  deposit  this  dissolved 
material  more  especially  on  their  upward  journey.  The  fact 

*  Trans.,  xxx.,  691 ;  p.  498  of  this  volume. 


696         THE   IGNEOUS   ROCKS   IN   THE    FORMATION    OF  VEINS. 

that  we  find  a  great  body  of  standing  water  not  far  below  the 
surface  in  regions  of  heavy  or  moderate  rainfall  would  make  it 
necessary,  according  to  this  conception,  to  believe  that  the 
rocks  are  pretty  thoroughly  saturated  with  water  down  to  the 
depths  at  which  the  return  journey  begins;  in  fact,  as  Van 
Hise  often  expresses  it,  there  exists  a  sea  of  the  groundwater. 
Van  Hise  in  particular  rejects  specifically  the  igneous  rocks  as 
significant  contributors  either  of  material  or  of  energy,  and 
expresses,  in  the  premises  or  propositions  which  he  seeks  to 
establish,  his  belief  that  the  waters  which  fill  the  veins  with 
minerals  are  meteoric,  and  that  gravity  is  their  motive  power. 
It  is  fair  to  add  that  the  conception  is  a  time-honored  one,  and 
has  found  frequent  previous  expression ;  but  we  owe  to  Van 
Hise  an  exceptionally  clear  and  logical  exposition  of  it. 

There  are,  however,  grave  objections  to  this  conception,  and 
we  may  justly  examine  it  in  the  light  of  the  experience  which 
has  been  gained  in  very  deep  mines  and  wells,  as  well  as  on 
certain  general  theoretical  grounds. 

Experience  in  Deep  Mines  and  Wells. 

Mines  exceeding  2000  or  2500  ft.  in  depth  are  of  extremely 
modern  development.  In  several  important  instances  of  this 
class,  as  well  as  in  many  mines  of  smaller  depth,  it  is  possible 
to  impound  all  the  water  within  a  short  distance,  it  may  be 
within  500  ft.,  of  the  surface.  Below  this  level  the  workings 
are  dry  and,  in  a  few  cases,  dusty. 

The  copper-mines  on  Keweenaw  Point  are  most  favorable  in 
their  geological  structure  to  the  downward  passage  of  water. 
The  shafts,  several  of  which  are  now  between  4000  and  5000  ft. 
deep,  cut  a  series  of  sheets  of  trap  and  amygdaloid  that  dip  36° 
to  39°,  and  include  one  or  two  beds  of  conglomerate.  They 
are  fissured,  and  at  times  even  brecciated.*  As  shown  by  the 
chart  opposite  p.  167  of  the  Report  just  cited,  the  North  Tam- 
arack Shaft,  No.  3,  at  a  depth  of  3818  ft.  had  cut  73  different 
trap  and  amygdaloid  layers.  It  is  fair  to  infer  that  the  new 
shaft  which  has  recently  grounded  in  the  Calumet  conglomerate 
at  4760  ft.  must  have  cut  correspondingly  more.  Yet  the  deep 
workings  of  these  copper  mines  are  not  only  dry,  but  in  some 

*  Oeol.  Survey  of  Mich.,  vol.  v.,  part  i.,  p.  112. 


THE  IGNEOUS  ROCKS  IN  THE  FORMATION  OF  VEINS.    697 

cases  dusty ;  and  the  water  is  impounded  either  at  the  surface 
or  a  short  distance  down  the  shaft.  Such  water  as  trickles 
down  the  shafts  from  the  top  is  occasionally  baled  out,  and  water 
for  the  drills  has  to  be  specially  sent  down  into  the  headings. 

At  Calumet,  the  only  water  encountered  in  the  deeper  work- 
ings, or  indeed  below  some  such  depth  as  500  ft,  is  a  highly 
alkaline  variety,  tapped  in  insignificant  amounts  from  occa- 
sional fissures.  It  has  a  painful  effect  upon  cuts  and  is  avoided 
as  far  as  possible  by  the  miners.  As  a  whole,  the  rocks  are 
free  from  visible  water. 

Posepny  says  that  the  deep  workings  at  Przibram  have 
afforded  a  similar  experience.  Below  800  meters  there  is  no 
water  to  be  raised,  because  evaporation  removes  whatever  exists 
there.  Much  that  has  been  pumped  from  the  levels  immedi- 
ately above  800  meters  is  doubtless  water  that  has  escaped  im- 
pounding nearer  the  surface,  and  has  followed  down  the  open- 
ings made  by  the  mine  itself.  The  deepest  workings  at 
Przibram  mentioned  by  Posepny  are  1110  meters.* 

Experience  gained  in  the  deep  Cornish  tin-mines,  like  the 
Dolcoath,  would  be  important  in  this  connection,  but  at  the  time 
of  going  to  press  it  is  not  available.  Mr.  B.  B.  Lawrence  has 
mentioned,  in  some  informal  remarks  at  this  meeting,  the 
Pelican-Dives  mine,  near  Georgetown,  Colorado,  which  has 
now  attained  a  depth  of  over  2000  ft.  The  water  has  been 
allowed  to  follow  the  workings  down  and  is  raised  from  the 
bottom,  but  no  more  is  pumped  now  than  when  the  bottom 
sump  was  located  in  the  upper  levels. 

The  cases  cited  merely  express  the  general  experience  of 
mining  engineers,  all  of  whom  are  aware  that,  with  impounding 
of  the  surface-water,  increase  of  depth,  especially  below  2000 
ft.,  means  almost  invariably  dry  workings.  Even  if  the  rocks 
are  "  dry "  in  the  miner's  sense  only,  and  not  in  the  strict 
scientific  sense,  if  their  contributions  of  water  are  removed  by 
evaporation  so  as  not  to  be  noted ;  or  if,  in  a  great  artificial 
excavation,  far  larger  than  the  vast  majority  of  natural  water- 
ways, no  pumping  is  necessary,  the  water  in  the  rocks  may  be 
neglected  as  a  producer  of  veins.  The  deep  mines  which  are 
known  to  be  wet,  such  as  those  of  the  Com  stock  lode,  are  in 

*  Trans.,  xxiii.,  248;  xxiv.,  971. 


698    THE  IGNEOUS  KOCKS  IN  THE  FORMATION  OF  VEINS. 

regions  of  expiring  vulcanism,  as  will  be  emphasized  a  little 
further  on. 

Many  mines,  especially  collieries,  have  been  driven  under 
bodies  of  water,  and  even  under  the  sea,  and  yet  they  have 
been  but  slightly  if  at  all  troubled  by  water,  and  sometimes 
have  been  absolutely  free  from  it.  Tight  shales,  in  a  sedimen- 
tary series,  would  partly  account  for  this ;  nevertheless  the 
general  experience  is  worthy  of  emphasis. 

Artesian  borings  have  in  a  few  cases  yielded  similar  testimony. 
The  deep  well  near  Wheeling,  West  Ya.,  which  has  been  made 
famous  by  the  measurements  of  Professor  Wm.  Hallock  on 
the  increase  of  temperature  with  descent,  reached  a  depth  of 
4500  ft.  The  last  water  was  cased  off  at  1500  ft.,  so  that  for 
3000  ft.  the  hole  was  dry.  In  this  3000  ft.  the  well  penetrated 
shales  and  some  sandstones,  both  of  marine  origin.  Shales  are 
admittedly  the  least  favorable  of  rocks  for  circulating  waters,  but 
it  is  a  surprising  fact  that  this  great  section  afforded  a  dry  hole.* 
The  Pittsburgh  well  is  still  more  remarkable.  In  February, 
1897,  the  well  had  reached  a  depth  of  5386  ft.  It  was  cased 
only  to  900  ft.,  or  slightly  beyond,  and  for  over  4400  ft.  was  dry. 
The  well  penetrated  a  section  similar  to  that  at  Wheeling. 

On  the  other  hand,  the  deep  wells  at  Sperenberg,  Schlada- 
bach  and  Reibnik,  all  in  Germany,  are  wet,  so  far  as  the  pub- 
lished descriptions  of  the  measurements  of  temperature  inform 
us,  but  as  they  were  bored  with  the  diamond-drill,  it  is  believed 
that  they  were  not  cased.  I  have,  however,  no  definite  informa- 
tion regarding  this  point. 

All  these  facts,  except  the  last,  go  to  show  that  the  outer 
portion  of  the  globe  is  much  less  permeable  to  water  than  has 
often  been  assumed,  and  that,  in  many  places  at  least,  the  down- 
ward percolation  is  a  negligible  factor.  The  groundwater 
which  is  met  at  small  though  variable  depths,  and  which  fills 
abandoned  mine-workings,  is  held  there  by  the  tight  rocks  be- 
neath it,  and  is  not  to  be  considered  the  upper  part  of  a  mass 
of  water  reaching  down  to  10,000  ft.,  or  any  such  depth,  in  the 

*  Wm.  Hallock,  Proc.  Amer.  Assoc.  Adv.  ScL,  xl.,  257,  1891  ;  School  of  Mines 
Quarterly,  xviii.,  148,  1897.  The  latter  gives  details  of  the  Pittsburgh  well  also. 
The  section  of.  the  well  at  Wheeling  will  be  found  in  West  Va.  Geological  Survey, 
vol.  i.,  p.  364,  1899.  Professor  Hallock  states  that  the  well  was  plugged  with  an 
oak  plug  after  his  measurements ;  two  years  later,  when  the  plug  was  removed, 
the  hole  was  full  of  water,  which  all  believed  leaked  in  at  the  end  of  the  casing. 


THE    IGNEOUS    ROCKS    IN    THE    FORMATION    OF  VEINS.         699 

interior.     On  the  contrary,  something  like  2000  ft.  appears  to 
be  its  limit,  arid  in  some  regions  it  ceases  at  500  ft. 

The  explanation  lies,  no  doubt,  in  the  plugging  of  fissures 
and  crevices  with  attrition  or  residual  clay,  and  in  the  feeble- 
ness or  disappearance  of  capillary  attraction  with  increase  of 
pressure.  The  efficiency  of  a  very  thin  seam  of  clay  in  keeping 
back  water  is  well  known  to  all  miners  who  have  been  engaged 
in  wet  ground.  A  layer  a  quarter-inch  thick  is  water-tight, 
and  often  every  precaution,  as  remarked  by  Dr.  Raymond  at 
the  present  meeting,  is  taken  by  the  miners  not  to  break 
through  even  this  small  thickness.  As  to  the  efficiency  of 
capillary  attraction  with  increase  of  pressure,  I  learn  from  Prof. 
R.  S.  Woodward,  as  I  have  already  said,  that  our  knowledge  is 
very  limited,  and  he  at  least  would  hesitate  to  affirm  that  it 
operates.  It  has  been  shown,  moreover,  as  I  am  informed  by 
Dr.  A.  A.  Julien,  that  when,  in  testing  the  absorption  of  build- 
ing-stones, pieces  are  merely  soaked  in  water,  the  penetration 
of  the  water  is  insignificant ;  but  if  the  air  in  the  stone  is  ex- 
hausted under  an  air-pump,  or  by  boiling,  or  if  the  block  of 
stone  rests  on  wet  felt,  then  absorption  takes  place. 

The  extraordinary  impenetrability  of  some  rocks  is  emphat- 
ically shown  by  the  storage  of  petroleum  and  natural  gas. 
Both  of  these,  but  more  especially  the  former,  are  wanderers 
to  a  remarkable  degree,  yet  they  are  confined  in  the  ground 
under  very  great  pressure  and  are  unable  to  escape.  Edward 
Orton,  Sr.,  satisfactorily  demonstrated  in  1889  that  the  pressure 
of  the  gas  in  the  comparatively  shallow  wells  of  Ohio  (1000  ft.) 
was  hydrostatic  and  due  to  the  groundwater.  Nearly  all  geolo- 
gists believed  the  same  agent  to  be  the  universal  cause  of  the 
rock-pressure  of  natural  gas ;  but  when  the  deep  gas-wells  of  New 
York  were  drilled  from  2250  to  2600  ft,  to  the  Trenton  lime- 
stone, it  was  found  that  some  other  factor  must  enter,  because 
the  pressure  is  too  great  for  a  hydrostatic  cause.  Prof.  Orton, 
therefore,  and  others  with  him,  have  abandoned  this  view.* 

In  some  deep  mines  water  has  been  encountered  in  uprising 
springs,  and  the  same  is  true  of  not  a  few  shallow  shafts;  but  I 
do  not  think  that  any  springs  at  less  than  1500  or  2000  ft. 
depth  have  a  bearing  on  this  question.  Posepnyf  mentions 

*  Bull  Geol  Soc.  Amer.,  ix.,  95-99.  f  Trans.,  xxiii.,  223. 


700         THE   IGNEOUS    ROCKS   IN   THE   FORMATION    OF  VEINS. 

one  in  the  Einigkeit  shaft,  Joachimsthal,  Bohemia,  that  was 
met  at  533  meters  (1774  ft);  but  in  the  next  paragraph  we 
learn  that  the  uprising  waters  at  Joachimsthal  were  tapped 
along  the  contacts  of  the  veins  with  basaltic  rocks  of  com- 
paratively late  origin,  and  therefore  in  a  situation  involving 
expiring  vulcanism.  I  do  not  cite  this  and  the  subsequent 
cases  with  a  view  of  necessarily  referring  the  waters  to  exhala- 
tions from  fused  and  consolidating  or  consolidated  magmas, 
but  I  do  mean  to  use  them,  along  with  other  considerations,  to 
show  the  impotence  of  purely  gravitative  motive  power. 

The  Comstock  lode  is  the  most  famous  case  of  a  deep,  wet 
mine.  Church,  King  and  Becker  have  all  discussed  the  waters 
in  their  several  monographs.  Water  was  tapped  on  the  2200- 
ft.  level  of  the  Savage,  and  rose  both  in  it  and  in  the  Hale  and 
Norcross  to  the  1750-ft.  level;  but  there  it  stopped. 

Mr.  Becker  says  that  two  kinds  of  water  have  been  met  in 
the  lode.  One  is  pent  up  in  confined  bodies.  It  was  the 
tapping  of  such  a  body  that  let  the  water  into  the  Savage  and 
Hale  and  ]STorcross,  as  just  observed.  In  another  case,  a  cross- 
cut from  the  Palmer  shaft  was  invaded  by  a  body  of  water  that 
rose  100  ft.*  and  had  a  temperature  of  104°  F.  The  other 
kind  of  water  rises  from  the  depths.  No  one  doubts  that  the 
high  temperature  of  these  waters  is  due  to  expiring  vulcanism, 
and  the  focus  of  the  heat  is  placed  by  Mr.  Becker  at  not  less 
than  two,  and  more  probably  four  miles  in  depth,  f  The  re- 
gion is  arid,  and  it  is  believed  that  the  water  must  have  come 
from  a  distance.  A  source  for  it  in  the  Sierras,  12  or  14  miles 
to  the  west,  is  tentatively  suggested  by  Mr.  Becker ;  but  there 
is  good  reason  for  thinking  some  of  it,  at  least,  to  be  a  con- 
tribution from  the  eruptives  themselves. 

EmmonsJ  has  recorded  a  very  interesting  case  of  an  uprising 
spring  in  the  Geyser  mine  at  Silver  Cliff,  Colo.  The  shaft  was 
sunk  so  that  it  cut  at  2000  ft.  the  contact  between  overlying 
porous  rhyolite  tuff  and  the  underlying  granite.  Water  in 
small  amount  and  charged  with  carbonic  acid,  and  different  in 
composition  from  the  descending  waters,  which  had  ceased  far 
above,  bubbled  into  the  workings  along  small  fissures  parallel 

*  Fortieth  Parallel  Survey,  iii.,  87. 

f   U.  S.  GeoL  Sur.,  Monograph  III.,  p.  264. 

$  17 'th  Ann.  Rep.  Dir.  U.  S.  GeoL  Survey,  part  ii.,  p.  458. 


THE  IGNEOUS  ROCKS  IN  THE  FORMATION  OF  VEINS.    701 

with  the  contact.  Here,  again,  the  spring  is  in  a  region  of  vul- 
canism  of  rather  recent  date,  geologically  speaking,  and  it  is 
impossible  to  assert  that  an  abnormal  rise  in  the  isogeotherms 
from  this  cause  is  not  a  factor  in  the  circulation,  although  the 
water  exhibited  only  the  temperature  of  the  drifts  themselves. 

It  is  not  my  purpose  to  attempt  to  show  that  water  does  not 
descend  into  the  earth  below  2000  ft.,  for  I  believe  that  it  does, 
although  not  by  any  means  in  the  amounts  which  have  some- 
times been  assumed.  I  wish  to  make  clear  that  the  amount  is 
probably  comparatively  small;  that  there  are  good  grounds 
for  believing  that  it  only  descends  to  great  depths  by  relatively 
large  fissures ;  and  that  these  are  exceptional.  To  the  same 
degree  that  the  meteoric  waters  are  limited  to  the  relatively 
large  fissures,  they  are  unfavorably  situated  for  the  solution  of 
sparsely  distributed  minerals  and  metals.  I  hope  to  establish, 
further  on,  that  even  if  they  descend  in  this  way,  by  a  trickle  here 
and  a  little  seepage  there,  they  can  never  be  brought  again  to 
the  surface,  so  as  to  form  springs,  by  gravity  and  the  normal 
rise  of  temperature  alone. 

At  the  same  time,  I  fully  recognize  that  there  is  ground  for 
a  different  view,  and  that  a  strong  case  can  be  made  out  for  the 
very  slow  circulation  of  water  at  great  depths.  But  even  if  it  be 
admitted  that  this  is  the  case ;  that  the  waters  become  charged 
with  ores;  and  that  they  have  some  tendency  to  pass  upward, 
by  reason  of  the  heat  acquired  through  the  normal  rise  of  tem- 
perature with  depth ;  it  remains  true  that,  in  again  ascending, 
they  meet  descending  currents  or  mingle  with  relatively  station- 
ary water;  and  they  become  dilute  and  disseminated  and  com- 
paratively weak  agents,  when  contrasted  with  the  much  supe- 
rior efficiency  which  may  be  locally  conferred  upon  waters  by 
igneous  intrusions.  While  one  cannot  deny  that,  by  the  former 
type  of  circulation  and  in  the  long  course  of  geological  time, 
something  might  be  accomplished,  yet,  a  fortiori,  all  the  results 
might  have  been  brought  about,  and  there  is  abundant  reason 
to  think  that  they  were  brought  about,  by  the  aid  of  igneous 
rocks,  as  I  shall  endeavor  to  show  subsequently,  by  proof  ad- 
ditional to  what  has  already  been  said. 

The  interrupted  passage  of  the  waters,  when  they  do  de- 
scend, has  an  important  bearing  upon  the  hydrostatic  head. 
Whenever,  for  example,  capillary  transmission  occurs,  the  pre- 


702         THE   IGNEOUS   ROCKS   IN    THE   FORMATION    OF  VEINS. 

viously  acquired  head  is  lost,  and  the  emerging  water  proceeds 
on  its  way  only  under  a  newly  accumulating  head.  So  far, 
therefore,  as  capillary  transmission  may  be  assumed,  ordinary 
calculations  of  hydrostatic  pressure,  based  on  distances  from 
the  surface,  are  false.  In  any  event,  even  with  the  assumption 
of  channels  larger  than  capillaries,  we  are  forced  in  these  calcu- 
lations to  believe  in  the  practically  standing  body  of  water, 
reaching  nearly  to  the  surface,  to  which  objections  have  been 
already  raised. 

Artesian  Basins. 

The  experience  which  has  been  gained  with  artesian  wells 
is  the  chief  foundation  of  much  that  has  been  written  upon  the 
circulation  of  the  groundwater ;  and  yet  artesian  basins  furnish 
one  of  the  strongest  arguments  for  the  storage  of  water  compara- 
tively near  the  surface,  and  against  its  descent  to  great  depths. 
Within  the  limits  of  an  area  thus  supplied  with  underground 
reservoirs,  it  is  obviously  impossible  for  waters  to  descend  be- 
low the  impervious  stratum  which  is  the  cause  of  the  reservoir, 
and  it  would  follow  that  the  lower  lying  rocks  would  be  dry, 
except  so  far  as  they  are  supplied  with  waters  which  have  mi- 
grated in  from  points  on  the  surface  outside  the  limits  of  the 
catchment-area.  In  many  cases  this  would  involve  a  journey 
of  many  miles,  possibly  more  than  a  hundred. 

Artesian  basins  of  themselves  permit  but  slight  circulation 
of  the  imprisoned  waters,  and  are  most  unfavorable  places  for 
the  formation  of  anything  like  veins.  They  represent  just  so 
much  water  cut  off*  from  active  work,  like  a  convict  in  a  peni- 
tentiary. They  may  occasionally  be  tapped  off,  downward  or 
upward,  by  faults,  just  as  once  in  a  while  a  convict  escapes, 
and  then  the  waters  may  become  geologically  active.  If  they 
are  invaded,  however,  by  igneous  intrusions  with  the  attendant 
cracking  of  the  overlying  rock,  the  accession  of  heat  or  energy 
may  make  them  again  active  agents.  The  standing  waters, 
and,  what  is  practically  the  same  thing,  the  waters  which  rest 
under  such  pressure  that  they  do  not  reach  the  surface  and 
flow  off,  are  considered  to  be  too  inefficient  to  be  important  in 
the  formation  of  veins. 

In  cases  like  the  Wheeling  and  Pittsburgh  wells,  in  which 
from  3000  to  4500  ft.  of  marine  sediments  are  apparently  dry, 
one  cannot  but  wonder  what  has  become  of  the  sea-water  which 


THE    IGNEOUS    ROCKS    IN    THE    FORMATION    OF  VEINS.          703 

they  must  have  contained  when  they  were  deposited.  Instead 
of  receiving  new  supplies,  they  have  apparently  been  deprived 
even  of  the  little  which  they  did  possess.  Undoubtedly  the 
pressure  of  overlying  masses  has  effected  this  result,  or  else  the 
water  has  become  combined  in  some  chemical  way  in  the  rock 
itself,  and  has  been  thus  locked  up. 

Hot  Springs. 

The  most  suggestive  of  all  geological  phenomena  in  connec- 
tion with  the  formation  of  veins  are  hot  springs ;  and  there  is 
ground  for  believing  that  they  cannot  be  explained  on  any 
other  assumption  than  that  of  an  abnormal  local  rise  in  the 
isogeotherms.  As  Osmond  Fisher  has  shown,*  the  isogeotherms 
cannot  conceivably  be  raised  except  by  igneous  intrusions  or 
by  the  mechanical  production  of  heat  along  faults,  or  belts  of 
shattering :  and  the  latter  do  not  compare  in  effectiveness  with 
the  former. 

If  for  a  moment  we  analyze  the  familiar  increase  of  tempera- 
ture with  descent,  a  truer  conception  will  be  gained.  As  ordi- 
narily stated,  and  as  a  fair  average,  it  may  be  assumed  that  the 
temperature  increases  one  degree  Centigrade  for  each  thirty 
meters  of  descent,  which  would  be  about  one  degree  Fahren- 
heit for  each  55  ft.  In  a  region  whose  mean  annual  tempera- 
ture is  50°  F.  or  10°  C.  (that  of  New  York  is  about  51°  F.), 
in  order  to  reach  a  depth  at  which  the  temperature  is  100°  C. 
we  would  be  obliged  to  descend  2700  meters,  or  not  far  from 
10,000  ft.  Now  that  meteoric  waters  may  flow  from  the  sur- 
face as  a  hot  spring,  which  has  derived  its  abnormal  heat  from 
this  deep-seated  source,  they  must  descend  to  a  depth  which  is 
at  least  a  large  fraction  of  10,000  ft.  and  then  return.  The 
depth  is  a  larger  fraction  of  the  10,000  ft.  than  the  temperature 
of  the  spring  would  of  itself  indicate,  because  the  uprising 
waters  have  traversed  cooler  rocks  and  necessarily  have  re- 
ceived accessions  of  descending  colder  waters.  One  other  im- 
portant factor  bearing  on  this  question  is,  moreover,  the  ir- 
regular and  more  or  less  choked  conduits  which  have  already 
been  emphasized. 

The  following  argument  has  been  sometimes  advanced,  and 

*  Physics  of  the  Earths  Crust,  pp.  240-241. 


704         THE    IGNEOUS    ROCKS    IN    THE    FORMATION    OF  VEINS. 

notably  by  Van  Hise,*  in  supporting  the  view  that  hot  springs 
are  the  result  of  normal  terrestrial  circulations,  without  acces- 
sions of  heat  other  than  those  which  would  be  received  through 
the  ordinary  increase  of  temperature  with  depth.  It  is  argued 
that,  as  the  descending  column  of  cold  water  is  heavier,  and 
the  ascending  column  of  heated  water  is  lighter,  therefore  a 
hydrostatic  head  is  afforded.  Water  expands  about  4  per  cent, 
between  0°  C.  (or,  more  precisely,  4°  C.)  and  100°  C.,  and, 
for  illustration,  the  case  is  imagined  of  a  descending  column  at 
0°  and  an  ascending  one  at  100°.  This  assumption,  or  any 
similar  one,  loses  practically  all  its  force  if  we  bear  in  mind  the 
following  important  considerations : 

1.  That  the  descending  column  becomes  gradually  heated,  so 
that,  even  if  the  conduits  formed  practically  a  long  U-tube, 
there  would  be  little  difference  in  head. 

2.  That  the  descending  column  may  move  in  part  in  a  capil- 
lary way  and  lose  its  head. 

3.  That  water  under  great  load  or  pressure  does  not  expand 
according  to  the  4  per  cent,  rate  named.     On  the  contrary,  it 
may  be  held  by  the  pressure  at  fixed  volume,  despite  the  added 
heat.     If,  for  example,  we  roughly  assume  a  column  of  water, 
one  square  inch  in  cross-section  and  two  feet  high  (it  is  really 
about  2  ft.  3J  in.)  as  equal  to  a  pressure  of  a  pound  to  the 
square  inch,  in  10,000  ft.  we  would  have  a  pressure  of  some- 
thing near  5000  Ibs.  or  over  2  tons  to  the  square  inch;  and  in 
the  face  of  this  the  expansion  of  water  from  an  added  tempera- 
ture of  100°  C.  practically  becomes  a  negligible  quantity  as 
contributing  to  hydrostatic  head. 

4.  We  must  bear  in  mind  also  that  the  standing  body  of  cold 
groundwater  fills  the  interstices  of  all  rocks  near  the  surface, 
except  those  in  very  arid  regions,  and  exerts  a  retarding  influ- 
ence on  uprising  currents. 

When  these  objections  are  all  appreciated,  I  think  we  must 
admit  that,  except  so  far  as  waters  are  fed  from  heights  into 
artesian  basins  and  thence  tapped  again  to  the  surface,  per- 
haps slightly  warmed  from  having  gone  to  comparatively  shal- 
low depths,  such  a  theory  of  hot  springs,  or  even  of  warm 
springs,  is  impossible.  Hot  springs  can  only  be  developed  in 

*  "Some  Principles  Controlling  the  Deposition  of  Ores,"  Trans.,  xxx.,  48;  p. 
303  of  this  volume. 


THE    IGNEOUS    ROCKS    IN    THE    FORMATION    OF  VEINS.          Y05 

the  presence  of  an  abnormal  rise  of  the  isogeotherms,  which 
rise  can  only  be  eifectively  produced  by  intruded  masses  of 
igneous  rock.  I  will  even  go  so  far  as  to  say  that  it  is  in  the 
highest  degree  improbable  that  any  waters  which  have  reached 
depths  even  approximating  10,000  ft.  can  ever  again  reach  the 
surface  and  yield  flowing  springs,  except  through  the  propul- 
sion of  stores  of  energy  contributed  by  still  heated  masses  of 
igneous  rock.  I  regard  it  as  extremely  improbable  that  the 
water  of  any  natural  spring,  whose  flow  is  due  simply  to  hydro- 
static head,  has  ever  reached  more  than  a  very  limited  depth 
below  the  point  of  emergence.  These  statements  are  made  in 
the  belief  that  unless  underground  water  ultimately  emerges 
upon  the  surface,  so  as  to  maintain  an  activity  of  movement 
which  this  condition  implies,  its  efficiency  is  so  slight  and  its 
stagnation  so  pronounced  that  it  is  of  small  probable  import- 
ance in  connection  with  vein-formation  of  any  magnitude. 
Professor  Sandberger  and  those  who  stand  with  him  are  the 
only  logical  lateral-secretionists. 

Even  in  areas  showing  the  structure  of  an  artesian  basin,  and 
possessing  a  theoretical  head  of  hundreds  of  feet,  the  water 
sometimes  rises  to  a  given  level  in  a  well  and  then  stands  below 
the  surface.  Abnormally  heated  waters,  such  as  those  of  South 
Dakota,  described  by  N".  H.  Darton,*  can  only  be  accounted 
for  by  the  presence  of  eruptives,  although  Mr.  Darton  seems 
loath  even  to  mention  igneous  rocks  as  a  possible  explanation. 
Yet  they  would  appear  to  be  the  only  reasonable  one,  and  in 
this  region  there  is  ground  for  inferring  their  existence. 

In  passing  from  laboratory-experiments  in  hydraulics  to  the 
phenomena  of  the  earth,  there  is  grave  danger  of  error  unless 
one  proceeds  with  great  caution.  It  is  much  the  same  difficulty 
that  formerly  arose  in  drawing  profiles  of  country  with  exag- 
gerated, vertical  scales.  The  sense  of  true  perspective  was 
lost.  Mr.  Klckard's  illustrative  figure  of  the  hot-water  circula- 
tions in  a  household  heating-plant,  f  likewise  cited  by  Professor 
Van  Hise,  would  give  a  very  false  conception  unless  used  with 
so  much  allowance  as  to  be  destructive  of  its  force.  The  open 
pipes  in  a  house,  extending  but  50  or  100  feet  in  altitude,  and 

*  Am.  Jour,  of  Sci.,  March,  1898,  p.  161,  and  especially  p.  168. 
f  Trans.,  xxiv.,  950. 


706    THE  IGNEOUS  ROCKS  IN  THE  FORMATION  OF  VEINS. 

with  an  intense  source  of  heat  in  the  cellar,  are  not  comparable 
to  conduits  of  irregular  size,  often  choked,  at  times  capillary, 
and  with  10,000  feet  of  gradually  warming  walls  before  even  a 
temperature  of  100°  C.  is  reached. 

In  brief,  therefore,  I  believe  it  to  be  highly  improbable  that 
hot  springs  are  ever  produced  except  in  regions  of  expiring 
vulcanism ;  but  it  is,  on  the  other  hand,  highly  probable  that 
hot  springs  have  been  the  great  producers  of  veins. 

The  Irregular  Distribution  of  the  G-roundwater  near  the  Surface. 

Recent  observations  of  Emmons  and  Weed  have  emphasized 
the  fact  that  the  level  of  the  groundwater  is  not  a  regular  and 
sharply  marked  surface,  but  is,  on  the  contrary,  very  irregular 
and  subject  to  much  fluctuation.  The  presence  of  oxidized  or 
enriched  minerals  in  some  places  at  depths  below  the  ordinary 
groundwater  level  has  given  rise  to  this  inference.  It  would 
appear  as  if  waters  become  charged  with  metals  within  the 
limits  of  the  gossan,  and,  descending,  react  on  leaner  sulphides 
so  as  to  enrich  them,  and  that  they  do  so  even  by  diffusion 
through  the  standing  groundwater  and  below  its  level.  But  it 
also  appears  as  if  there  were  no  standing  groundwater  and  no 
means  of  preventing  quite  deep  oxidation  and  enrichment  along 
some  belts,  which,  because  of  their  open  character, 'may  allow 
the  waters  to  go  down,  turn  and  rise  again  as  a  spring  at  some 
lower  point;  and  this,  although  neighboring  ground,  impervious 
in  character,  may  retain  the  groundwater  at  a  sharply  marked  and 
higher  definite  level.  Naturally,  in  interpreting  the  phenomena 
of  gossan-minerals  apparently  carried  downward,  we  must  bear 
in  mind  the  later  geological  history  of  the  district,  because  sub- 
sidence, together  with  the  choking  and  elevation  of  surface- 
drainage,  may  raise  the  groundwater  above  its  old  level,  and  it 
may  be  that  some  of  the  minerals  regarded  as  enriched  (bornite, 
chalcocite,  etc.)  have  been  deposited  by  uprising  currents. 

In  regions  where  the  rainfall  is  small,  and  where  the  con- 
tributions to  the  groundwater  are  correspondingly  slight,  its 
level  may  be  very  far  down ;  or,  if  the  rocks  are  shattered, 
standing  groundwater  may  be  entirely  lacking,  and  oxidized 
ores,  so  far  as  they  can  be  produced  without  the*  aid  of  much 
water,  may  extend  to  depths  indefinitely  great.  On  the  other 
hand,  in  an  arid  region  galena  may  actually  outcrop.  In  the 


THE  IGNEOUS  ROCKS  IN  THE  FORMATION  OF  VEINS.    707 

Geological  Museum  of  the  Columbia  School  of  Mines  there  is 
a  large  specimen,  about  a  cubic  foot  in  volume,  that  was  pried 
out  of  the  cropping  ot  the  Half-Moon  vein  at  Pioche,  ETev.,  by 
Prof.  Geo.  "W.  Maynard.  It  is  galena  and  quartz,  the  former 
only  oxidized  on  the  surface. 

All  of  these  points  are,  however,  matters  of  the  anatomy  or 
pathology  of  already-formed  veins,  and  do  not  touch  the  fun- 
damental problems  of  genesis,  to  which,  in  fact,  they  are  re- 
lated much  as  are  bodily  disorders  and  amputations  to  embry- 
ology and  growth. 

III. — THE  DISTRIBUTION  OF  MINING  DISTRICTS. 

When  one  considers  the  country  at  large  (leaving  iron-ores 
out  of  the  question),  it  is  evident  that  districts  favorable  to 
actual  mining  are  very  sparsely  distributed.  Even  in  regions 
like  the  mountainous  parts  of  Colorado  and  Montana,  where 
we  commonly  think  of  mining  as  being  extensively  practiced, 
the  productive  areas  are  separated  by  vast  stretches  of  country 
without  workable  and,  I  think  one  may  say,  without  notable 
vein-development.  One  rides  in  a  train  for  hours  between  the 
camps,  and  only  for  minutes  in  them.  Even  making  due  allow- 
ance for  lack  of  outcrops,  for  forests  and  for  veins  concealed  by 
the  wash,  the  mining  districts  must  be  described  as  limited 
areas  of  intense  local  vein-formation,  which  alternate  with  vast 
areas  of  barren  ground. 

In  the  mining  districts  igneous  rocks  are  present,  practically 
without  exception.  If  we  assert  that  the  assumed  circulations 
of  meteoric  waters,  which  are  thought  to  be  universal  in  the 
rocks,  and  to  be  due  to  the  ordinary  and  ever-present  increment 
of  temperature  with  depth,  are  the  causes  of  vein-formation,  we 
encounter  grave  difficulties  in  trying  to  explain  this  general 
absence  of  veins.  Dislocations  are  everywhere  present,  and  we 
ought  to  find  veins  in  a  similarly  great  abundance.  On  the 
other  hand,  if  we  remember  the  points  made  regarding  the  igne- 
ous rocks  at  the  outset,  we  shall  have  a  much  more  rational  ex- 
planation both  of  the  presence  and  of  the  absence  of  the  veins. 

It  must  be  appreciated  by  all  who  are  adequately  familiar 
with  both  the  literature  and  the  phenomena,  or  with  either,  that 
ore-bearing  veins,  especially  when  of  large  size,  are  altogether 
exceptional  and  rare  occurrences,  and  their  causes  are  local  and 

45 


708         THE    IGNEOUS    ROCKS    IN    THE    FORMATION    OF  VEINS. 

exceptional  in  their  nature.  ISTo  one  with  a  correct  sense  of 
perspective  can  possibly  be  face  to  face  with  the  huge  stopes  of 
ores  of  comparatively  scarce  metals,  which  some  of  our  mines 
afford,  without  marveling  greatly  that  they  ever  happened  to  be 
produced  in  the  course  of  Nature;  and  in  dealing  with  the  elu- 
sive but  irresistibly  attractive  problems  which  their  genesis 
affords,  one  cannot  be  too  appreciative  of  the  local  and  excep- 
tional nature  of  the  causes  which  have  produced  them.  One 
may,  therefore,  in  endeavoring  to  explain  vein-phenomena  as  a 
minor  corollary  to  an  all-embracing  theory  of  metamorphism, 
based  on  the  normal  circulations  of  the  groundwaters,  miss  the 
very  kernel  of  the  matter  and  fall  into  the  same  error  that  von 
Buch  and  other  disciples  of  Werner  committed,  in  the  early 
part  of  the  nineteenth  century,  in  endeavoring  to  establish  for 
rocks  in  general  a  "  universal  hypothesis." 

RESUME. 

The  thesis  of  vein-formation,  however  presented,  is  neces- 
sarily one  of  greater  or  less  probability,  rather  than  one  of 
demonstration.  The  following  points  may  be  made  in  favor 
of  igneous  rocks. 

1.  Igneous  rocks  contain  the  metals  and  the  elements  of  the 
gangue  minerals  more  abundantly  than  do  sedimentary  rocks. 

2.  Igneous  rocks   are    richly  provided  with  vapors  which 
come  up  with  them  from  great  depths.     Igneous  rocks  are 
enormous  reservoirs  of  energy. 

3.  Igneous  districts,  or  districts  of  combined  igneous  and 
sedimentary  rocks,  are  almost  always  the  geological  formations 
in  which  veins  occur. 

4.  The  vapors  and  solutions  from  intruded  igneous  rocks  are 
pre-eminently  favorable  chemical  reagents. 

5.  Observations  in  deep  mines  and  the  data  from  very  deep 
wells  indicate  the  general  absence  of  free  water  in  the  rocks 
below  moderate  depths,  except  in  regions  of  expiring  vulcan- 
ism.     This  is  a  grave  objection  to  the  conception  of  universal 
groundwater. 

6.  Capillary  attraction  is  largely  an  ascensive  force  and  of 
problematic  existence  with  increasing  pressure.     Artesian  res- 
ervoirs of  themselves  are  unfavorable  to  extended  circulation. 
There  is  a  strange  absence  of  the  original  content  of  water  in 


THE  IGNEOUS  KOCKS  IN  THE  FORMATION  OF  VEINS.    709 

deep-seated  sediments.     Standing  water  in  abandoned  shafts 
is  strong  evidence  of  the  impenetrability  of  rocks. 

7.  Hot  springs  are  necessarily  connected  with  an  abnormal 
rise  of  the  isogeotherms,  and  this  can  only  be  explained  by  in- 
truded igneous  rocks  or  by  faults  and  shattering.     The  latter 
do  not  compare  with  the  former  as  an  efficient  cause. 

8.  The  distribution  of  the  groundwater  is  far  less  uniform 
than  has  been  supposed.     The  groundwater  may  entirely  fail 
in  arid  regions. 

9.  The  distribution  of  mining  districts  can  only  be  satisfac- 
torily explained  by  the  corresponding  distribution  of  igneous 
rocks,  which  have  been  intruded  under  circumstances  favorable 
to  vein-formation.     Under   any  other  view  veins    should   be 
much  more  common. 

In  conclusion,  I  cannot  forbear  reference  to  the  subject  of 
the  classification  of  ore-deposits.  In  November,  1892,  I  pub- 
lished in  the  School  of  Mines  Quarterly  a  paper  on  the  "  Classi- 
fication of  Ore-Deposits,  a  Review,  and  a  Proposed  Scheme 
Based  on  Origin."  The  same  has  been  subsequently  printed, 
with  one  or  two  minor  modifications,  in  the  "  Ore-Deposits  of 
the  United  States."  After  a  review  of  all  the  known  schemes 
up  to  that  time,  and  an  analysis  of  their  special  features,  a 
scheme  was  developed  which  sought  more  consistently  than 
had  been  done  up  to  that  time  to  bring  the  ore-deposits  under 
well-recognized  geological  phenomena.  Aside  from  the  ores 
of  igneous  origin,  and  the  placers  of  various  kinds,  this  in- 
volved a  classification  of  those  phenomena  which  would  give 
rise  to  cavities,  not  of  themselves  necessarily  great,  but  sufficient 
to  furnish  a  water-way.  These  are  the  determining  factors  in 
the  location  of  ore-deposits ;  they  admit  of  the  least  possible 
difference  of  theoretical  views  or  of  interpretation,  and  they  are 
the  common  ground  upon  which  observers  can  best  meet  in  har- 
mony. They  therefore  furnish  much  the  best  basis  of  classifica- 
tion. I  do  not  believe  that  any  other  line  of  attack  of  this  problem 
furnishes  equal  advantages.  Therefore,  while  the  conceptions  of 
ascending  and  descending  waters  cited  by  Professor  Van  Hise  in 
closing  his  essay  give  new  and  significant  points  of  view,  yet  the 
interpretation  of  the  phenomena  in  accordance  with  them  is  in- 
evitably destined  to  raise  such  well-grounded  differences  of 
opinion  as  to  make  the  scheme  impracticable  for  general  use. 


710  THE    CALICHE    OF    SOUTHERN    ARIZONA. 


The  Caliche  of  Southern  Arizona  :    An  Example  of  Depo- 
sition by  the  Vadose  Circulation. 

BY  WILLIAM  P.  BLAKE,  F.G.S., 
Director  Arizona  School  of  Mines,  Tucson,  Ariz. 

(Richmond  Meeting,  February,  1901.) 

IN  southern  Arizona  and  in  Mexico  the  word  caliche  is  in 
general  use  to  denote  a  calcareous  formation  of  considerable 
thickness  and  volume  found  a  few  inches,  or  a  few  feet,  beneath 
the  surface-soil,  upon  the  broad,  dry,  gravelly  plains  and  mesas. 

In  western  South  America  the  same  name  is  applied  to  the 
beds  of  crude  soda-niter  (Chili  saltpeter).  "While  these  deposits 
of  South  America  and  of  Arizona  are  totally  different  in  com- 
position, and  have  nothing  in  common,  except  that  both  occur  in 
layers  in  the  strata  near  the  surface,  it  is  probable  that  an  ex- 
planation of  the  origin  of  the  calcareous  beds  may  equally  apply 
to  the  accumulation  of  soda-niter  and  other  deposits  of  easily 
soluble  minerals.  But  the  name,  taken  from  the  Latin,  Calx, 
is  more  appropriate  to  the  calcareous  beds  than  to  those  of 
niter. 

Caliche  has  a  wide  distribution  in  the  arid  regions  of  Arizona 
and  Mexico.  It  is  usually  hidden  from  view  by  a  slight  cover- 
ing of  soil ;  but  it  is  easily  found  by  digging,  and  is  often  re- 
vealed by  a  flow  of  water  during  heavy  rains.  It  is  practically 
a  continuous  sheet,  from  three  to  fifteen  feet  thick,  of  earthy 
limestone  or  travertine,  through  which  the  smaller  plant-roots 
find  their  way  with  difficulty.  The  presence  of  this  compara- 
tively impervious  layer  of  cemented  earth  may  account  for  the 
absence  of  trees,  or  of  the  larger  shrubs,  over  wide  areas.  The 
shrubs  which  gain  a  foothold  are  those  whose  roots  do  not  ex- 
tend far  downwards,  and  which  do  not  require  much  water, 
such  as  Larrea  Mexicana  and  the  Cactacece.  If  trees  are  planted, 
it  is  necessary  to  break  up  the  caliche  by  blasting,  or  at  least  to 
crack  the  upper  layers.  The  top  of  the  caliche  is  more  dense 
and  solid  than  the  lower  portions.  The  surface  of  this  top 
crust,  or  layer,  is  comparatively  smooth,  though  undulating, 
while  the  lower  portions,  under  the  crust,  are  irregular,  cavern- 


THE    CALICHE    OF    SOUTHERN   ARIZONA. 

ous,  earthy  and  very  porous,  blending  gradually  with  the  ma- 
terials of  the  sandy  and  gravelly  beds,  from  which  they  are 
divided  by  no  sharply  defined  plane  of  stratification  or  separa- 
tion. The  caliche  invests,  surrounds  and  includes  sand-grains, 
gravel,  and  more  or  less  earthy  material,  but  seems  to  have  had 
the  power,  especially  in  its  upper  crust,  of  extruding  the  coarse 
materials  of  the  soil  to  a  great  extent. 

The  deposit  does  not  form  a  regular  horizontal  bed  conform- 
able with  the  rude  stratification  of  the  gravels  and  sands,  but 
conforms  roughly  with  the  general  surface,  rising  and  falling 
with  the  undulations  of  the  mesa.  There  are,  in  places,  repeti- 
tions of  the  compact  layers,  separated  by  a  few  inches  of  the 
amorphous  and  more  earthy  deposit. 

In  cross-fracture,  this  upper  crust  of  the  caliche  exhibits  dis- 
tinct, fine  lines  of  successive  layers,  in  thin  sheets,  along  which 
the  rock  splits  with  some  ease,  while  there  is  a  rude  columnar 
fibrous  structure  transverse  to  these  layers,  sometimes  in  diver- 
gent lines  from  below  upward.*  Close  observation  detects  in 
some  places  small  perforations,  like  pin-holes  at  the  top,  which 
enlarge  gradually  below  and  penetrate  the  entire  compact  crust, 
becoming  lost  in  the  irregular  amorphous  granular  mass. 
These  holes  are  often  occupied  by  rootlets  of  plants ;  but  this 
is  not  regarded  as  evidence  of  any  connection  between  the 
deposition  of  the  caliche  and  plant-life — a  cause  of  deposition  to 
which  great  importance  is  attached  by  some  authorities. f  The 
caliche  is  an  example  of  deposition  independently  of  the  influ- 
ence of  organic  agencies. 

In   chemical    composition   the    caliche  is  essentially  a  lime 

*  l '  Sorby  has  shown  that  in  the  calcareous  deposits  from  fresh  water  there  is  a 
constant  tendency  towards  the  production  of  calcite  crystals  with  the  principal 
axis  perpendicular  to  the  surface  of  deposit.  When  that  surface  is  curved,  there 
is  a  radiation  or  convergence  of  the  fibre-like  crystals,  well  seen  in  sections  of 
stalactites  and  of  some  calcareous  tufas."  Cited  by  Geikie,  Text-Book  Geology,  3d 
Edit.,  p.  150. 

t  Dana,  for  example,  citing  from  W.  H.  Weed,  says  :  "  Some  of  the  travertine 
deposits  of  Gardiners  River  and  elsewhere  are  a  result  of  the  growth  and  secre- 
tions of  conferva-like  plants."  (Geology ,  4th  Edit.,  p.  138.)  Geikie  says  :  "But 
besides  giving  rise  to  new  formations  by  the  mere  accumulation  of  their  remains, 
plants  do  so  also  both  directly  and  indirectly  by  originating  or  precipitating  chem- 
ical solutions,"  etc.  .  .  .  "  Some  observers  have  even  maintained  that  this  is  the 
normal  mode  of  production  of  calc-sinter  in  large  masses,  like  those  of  Tivoli." 
(Geology  3d  Edit,  p.  482.) 


712  THE    CALICHE    OF    SOUTHERN    ARIZONA. 

carbonate,  but  contains  some  calcium,  magnesium  and  alumi- 
num silicates,  as  more  fully  shown  by  the  result  of  an  analysis 
made  by  my  assistant,  Mr.  J.  S.  Mann,  in  the  laboratory  of 
the  Arizona  School  of  Mines : 

Calcium  carbonate  (CaCO3),  .  .  .         .  -         ."".     78.28 

Magnesium  carbonate  (MgCO3),  .  .  .         •        .       2.13 

Calcium  silicate  (CaSiO3),     .  .  .        <.  .        ;        .       5.57 

Aluminum  silicate  (Al2SiO5),  .  ...  ...        .7.37 

Ferric  oxide  (Fe2O3), •  L88 

Moisture  (H2O),     .        .        .        ...        .        .        .      1.20 

96.43 

This  caliche,  unlike  the  deposits  of  travertine  formed  in  the 
open  air,  is  not  sufficiently  compact  and  solid  to  be  useful  in 
construction,  as  was  the  travertine  of  ancient  Rome.  When 
calcined,  it  yields  good  caustic  lime,  which,  tempered  with 
sand,  makes  a  strong,  quick-setting  mortar  or  cement.  It  is 
quarried  and  used  for  this  purpose  in  some  places.  Occurring, 
as  it  does,  in  mixture  with  gravel  and  sand,  it  has  the  appear- 
ance of  an  artificial  mixture,  and  as  such  was  once  supposed  to 
have  been  laid  down  as  a  foundation  by  the  builders  of  the 
Casa  Grande  in  Arizona.  On  the  line  of  the  Phoenix  and 
Prescott  railway,  it  has  been  found  that  railway  ties  last  longer 
when  laid  in  the  caliche  then  in  ordinary  soil.  Analysis  of  this 
caliche  showed  that  it  did  not  differ  essentially  from  the  caliche 
of  other  places. 

The  great  plain  or  mesa  of  Tucson  affords  one  of  the  best 
examples  of  the  occurrence  of  the  caliche.  This  mesa,  which 
appears  like  a  great  plain,  is  in  reality  a  combination  of  gentle 
slopes  from  the  surrounding  mountains.  The  area  within 
which  the  phenomena  of  the  caliche  are  shown  is  probably  not 
less  than  400  square  miles,  and  lies  between  the  Santa  Cata- 
lina  Mts.  on  the  north,  the  Bincon  and  Rillito  mountains  and 
the  Santa  Eita  ranges  on  the  east,  and  the  Tucson  Mts.  on 
the  west.  Toward  the  south  and  northwest  the  country  is 
open  in  the  direction  of  the  valley  of  the  Santa  Cruz.  The 
Santa  Cruz  and  the  Rillito  are  the  visible  channels  of  drain- 
age ;  but  there  is,  in  addition,  an  extensive  underground  flow  of 
water  as  widely  spread,  possibly,  as  the  area  mentioned,  but 
probably  strongest  in  volume  under  and  near  the  river  chan- 
nels draining  to  the  northwest.  The  general  altitude  of  the 


THE    CALICHE    OP    SOUTHERN    ARIZONA.  713 

mesa  above  the  sea  is  from  2400  ft.  at  Tucson  to  3000  or  3400 
ft.  about  20  miles  eastward.  These  declining  slopes  are 
formed,  for  the  greater  part,  of  the  debris  of  the  surrounding 
granitic  and  gneissic  mountains — the  "  wash  "  or  gravel  and 
sand  which  has  been  washed  out  from  the  canons  through  ages 
of  erosion.  As  a  rule,  these  materials  are  rudely  stratified, 
the  coarsest,  heavier  gravels  lying  nearest  to  the  mouths  of 
the  canons.  In  a  well  90  ft.  deep,  near  the  University,  on  the 
mesa  about  five  miles  from  the  channel  of  the  Billito,  the  fol- 
lowing beds  were  passed  through,  but  the  strata  were  not 
sharply  defined : 

Section  of  the  Mesa,  to  Water-Level. 

Feet. 
Soil,  sandy  and  porous,       ........       1 

Caliche,       .         .         .        .        .        .        .        .        .        .        .       6 

Sand  and  gravel,         .        .         .        .        .         .         .         .         .12 

Argillaceous  earth  (red),    ........       2 

Sand  (red),          ..........       2 

Caliche,  soft  and  amorphous,        .......       2 

Sand,  hard, 6 

Sand  and  gravel  ("cemented"), 3 

Sand  cemented  and  aggregated  in  lumps,  .  ...     11 

Argillaceous  earth,  red,     .    '    . 


Argillaceous  earth  and  sand,  red, 
Sand  and  boulders  mixed,  . 
Water  in  sandy  bed,  .         .        . 


30 

8 
4 


Most  of  the  sand  and  gravel  not  enveloped  in  caliche  was 
found  well  filled  with  small  sparkling  crystals  of  calcspar, 
which  appears  to  be  the  cementing  substance  holding  the  grains 
of  sand  together. 

Wherever  these  gravels  have  been  pierced  by  wells  in  the 
vicinity  of  Tucson,  an  abundance  of  water  has  been  found  at  a 
depth  of  from  80  to  90  ft.,  or  even  less,  depending  upon  the 
altitude  of  the  surface.  This  water  seems  to  be  inexhaustible; 
at  least  it  is  in  such  quantity,  and  flows  so  freely,  that  the 
pumping-plant  at  the  University  can  be  run  continuously,  dis- 
charging a  6-inch  stream,  without  exhausting  the  supply  in  the 
well. 

The  general  composition  of  this  underground  water  is  shown 
in  the  annexed  table,  compiled  from  the  records  of  the  chemical 
laboratory  of  the  University  of  Arizona. 


714 


THE    CALICHE    OF    SOUTHERN    ARIZONA. 


Analyses  of  Well-  Waters  of  Tucson  and  Vicinity — Parts 
Per  100,000. 


Two  Miles 
N.  of  Uni- 
versity. 

R.  R. 

Well. 

Irrigating 

Well. 

Tucson 
City 
Water. 

Hoff's 
Well. 

Oracle. 

Tucson 
Water 
Works. 

Total  Soluble 
Salt 

24.5 

42.0 

26.0 

65.0 

45.0 

39.0 

42.8 

NaCl 

]  4 

3  0 

3.0 

4.4 

4.5 

3.4 

3.9> 

(Na,  K)2S04.. 
Na2CO3 

3.1 

2  0 

15.2 
1.3 

6.5 
1.0 

26.8 
1.8 

13.5 
1.5 

10.6 
2.0 

16.92 

(Ca,  Mg)  C03. 
CaSO4 

9.0 
1  0 

15.5 
trace 

9.5 
0.5 

22.0 
0.0 

16.5 
0.5 

14.5 
0.5 

18.56 
1.74 

SiO2 

3.0 

2.0 

2.0 

2.0 

2.0 

2.0 

3.10 

It  is  probable  that,  in  the  course  of  the  underground  now  of 
the  water  from  the  higher  levels  towards  the  Santa  Cruz,  there 
are  considerable  areas  of  basin-shaped  depressions  in  the  bed- 
rocks, where  water  accumulates  and  is  more  sluggish  in  its 
movement.  So,  also,  there  may  be  ancient  channels,  determining 
a  more  rapid  flow  than  in  other  places ;  in  each  case  there  may  be 
a  difference  in  the  amounts  of  solid  matters  held  in  solution. 

There  has  been  much  speculation  in  regard  to  the  origin  of 
the  caliche.  It  has  been  generally  assumed  to  be  a  deposition 
from  some  ancient  lake,  or  body  of  water,  once  covering  the 
area  in  which  it  is  found.  But  such  a  theory  is  untenable  when 
all  the  phenomena  are  considered.  The  formation  is  clearly 
the  result  of  the  upward  capillary  flow  of  calcareous  water, 
induced  by  constant  and  rapid  evaporation  at  the  surface  in  a 
comparatively  rainless  region. 

With  a  constant  supply  of  phreatic*  calcareous  water,  the 
second  great  essential  factor  in  the  formation  of  caliche  is  the 
continued  desiccating  atmosphere — a  condition  which  prevails, 
with  only  short  and  temporary  exceptions,  throughout  the  year. 
The  desert  and  semi-desert  regions  of  Arizona  are  character- 
ized meteorologically  by  the  unusual  dryness  of  the  air  and  its 
capacity  for  the  absorption  of  moisture,  and  the  maintenance 
of  continued  evaporation  from  the  soil,  which  determines  a 
constant  upward  movement  of  the  phreatic  water.  The  occa- 
sional rains  in  midsummer  and  midwinter  do  not  penetrate  to 
great  depths,  but  are  sufficient  to  leach  out  the  soil  to  the  depth 
of  a  few  inches  or  feet,  turning  the  calcareous  solution  back 

*  Eaux  phreatiques,  Daubre'e,  Les  Eaux  Souterraines  d  V  epoque  actuelle,  i.,  19. 


THE    CALICHE    OF    SOUTHERN    ARIZONA.  715 

and  downwards,  and  producing  the  denser  upper  crust,  where 
it  meets  the  upward  flow. 

Such  I  conceive  to  be  the  origin  of  the  caliche.  It  may  be 
called  a  subterranean  deposit  of  travertine ;  but  it  is  not  the 
result  of  a  flow  from  springs,  or  from  any  source  at  the  surface, 
or  by  the  lateral  movement  of  water.  Unlike  ordinary  traver- 
tine, it  is  the  result  not  of  descending  but  of  ascending  currents. 
The  ordinary  conditions  of  vadose  circulation  are  reversed. 
The  caliche  is  a  fine  example  of  the  formation  of  extensive 
calcareous  strata  in  the  midst  of  pre-existent  beds,  not  by  meta- 
somatic  processes,  but  by  precipitation  from  sources  below. 

This  explanation  may  apply  equally  well  to  some  other  subter- 
ranean deposits  in  arid  regions,  where  the  upward  flow  is  main- 
tained in  excess  of  any  downward  percolation.  It  may  apply,  pos- 
sibly, to  the  origin  of  soda-niter,  of  some  beds  of  gypsum,  and  of 
some  of  the  metallic  sulphides.  In  fact,  the  phenomena  of  depo- 
sition of  ores  in  mineral  veins  are  here  repeated  in  kind,  though 
not  in  form,  over  broad  and  approximately  horizontal  areas,  so 
as  to  make  bedded  deposits  instead  of  fillings  of  fissures. 

Surface-deposits  of  soluble  salts,  such  as  the  chlorides,  sul- 
phates and  carbonates  of  the  alkalies,  are  familiar  to  all  resi- 
dents of  arid  regions.  The  "  black-alkali "  of  the  Salt  River 
valley  in  Arizona,  so  injurious  to  vegetation,  is  an  example  of 
the  concentration,  by  evaporation  at  the  surface,  of  solutions  of 
carbonate  of  soda.  The  white  efflorescences  on  the  soil  in  the 
dry  season,  known  to  the  Mexicans  as  tequisquita,  are  familiar 
examples.  These  deposits  become  snow-white  in  a  dry  time, 
and  quickly  disappear  into  the  soil  during  a  rain-storm. 

The  presence  of  caliche  in  the  soil  over  extended  areas  in  the 
arid  regions  I  regard  as  good  evidence  of  the  existence  of  sub- 
terranean water.  The  possibility  of  a  change  of  conditions 
since  the  deposit  of  the  caliche  should,  however,  be  considered. 

I  have  elsewhere  directed  attention  to  the  possible  enrich- 
ment of  the  upper  portions  or  croppings  of  mineral  veins  by 
the  upward  flow  of  solutions  formed  by  the  decomposition  of 
the  ores  above  the  permanent  water-level  in  arid  regions,  and, 
conversely,  the  impoverishment  of  the  croppings  of  lodes  in 
regions  of  abundant  precipitation,  where  downward  circulation 
predominates.  The  copper-deposits  at  Ducktown,  Tennessee, 
afford  striking  illustrations  of  the  latter  process. 


716      CHARACTER   AND    GENESIS    OF    CERTAIN    CONTACT-DEPOSITS. 

The  Character  and  Genesis  of  Certain  Contact-Deposits.* 

BY  WALDEMAR  LINDGREN,   WASHINGTON,   D.    C. 
(Richmond  Meeting,  February,  1901.) 

CONTENTS. 

I.  CHARACTER  OF  THE  DEPOSITS,  716  :    Principal  Features,  716  (Form,  717  ;  Posi- 

tion, 717  ;  Constituent  Minerals,  717  ;  Exceptions,  717)  ;  Literature,  718  ;  Geo- 
graphic Distribution,  720  ;  (California,  720  ;  Idaho,  721  ;  Arizona,  723  ;  British 
Columbia,  723 ;  Northwest  Territory,  723  ;  Mexico,  724  ;  Other  Countries, 
725). 

II.  ORIGIN  OF  THE  DEPOSITS,  725  :  Contact- Metamorphism,  726  ;  Cause  of  Contact  - 

Metamorphism,  727  ;  Similar  Deposits  of  Different  Origin,  730  ;  Genetic  Classifi- 
cation, 730  ;  Relation  of  Pegmatite-  Veins  to  Ore-Deposits,  732. 

I. — CHARACTER  OF  THE  DEPOSITS. 

1.  Principal  Features. 

IN  many  schemes  of  classification  and  description  the  term 
contact-deposit  has  been  somewhat  loosely  applied  to  all  accumu- 
lations of  useful  minerals  (other  than  those  of  unquestioned 
sedimentary  origin)  which  are  enclosed  between  two  different 
rocks.  As  thus  used,  the  term  may  include  deposits  of  widely 
differing  origin,  and,  unless  qualified,  is  not  in  place  in  a  genetic 
classification.  The  present  paper  deals  with  a  special  class  of 
contact-deposits. 

In  many  geological  provinces,  granular  igneous  rocks,  such 
as  granite,  diorite  and  syenite,  have  broken  through  and  in- 
vaded sedimentary  rocks.  The  molten  magma  may  in  part 
have  reached  the  surface  and  there  solidified  with  relative 
rapidity  as  a  lava.  The  largest  masses  of  it,  however,  did  not 
reach  the  surface,  but  cooled  very  slowly  at  considerable  depth 
under  great  pressure,  and  eventually  consolidated  into  a  rock 
of  granitic  texture.  Uplifts  and  extensive  erosion  may  have 
followed;  and  at  the  present  day,  in  many  places,  thousands  of 
feet  of  material  have  been  removed,  bringing  to  the  surface  the 
intrusive  granular  rocks  and  their  once  deep-seated  contacts 
with  the  sedimentaries  which  they  shattered  at  the  time  of  in- 

*  Published  by  permission  of  the  Director  of  the  U.  S.  Geological  Survey. 


CHARACTER    AND    GENESIS    OF    CERTAIN    CONTACT-DEPOSITS.       717 

trusion.  Along  these  contacts,  bodies  of  useful  minerals  are 
often  found,  most  commonly  where  the  sedimentary  rock  is 
limestone,  or,  at  least,  calcareous. 

All  the  world  over,  this  group  presents  certain  characteristics, 
the  more  essential  of  which  are  the  following : 

Form. — The  deposits  generally  follow  the  contact,  but  are  ex- 
tremely irregular  in  detail,  and  almost  always  very  bunchy.  !N"o 
regular  law  has  been  recognized  as  governing  the  form  of  the 
ore-bodies,  which  are  sometimes  lenticular  masses. 

Position. — The  minerals  generally  occur  in  the  limestone 
or  calcareous  rock,  immediately  on  the  contact,  from  which 
they  rarely  extend  more  (usually  much  less)  than  a  hundred 
feet. 

Constituent  Minerals. — The  gangue  contains  garnet,  wollas- 
tonite,  epidote,  ilvaite  (lievrite),  amphibole,  pyroxene,  zoisite, 
vesuvianite,  quartz  and  calcite,  rarely  fluorite  and  barite.  The 
ore-minerals  are  specularite,  magnetite,  bornite,  chalcopyrite, 
pyrite,  pyrrhotite,  and,  more  rarely,  galena  and  zincblende. 
The  sulphides  may  carry  some  gold  and  silver,  usually  more  of 
the  latter  than  of  the  former,  but  are  rarely  rich.  Tellurides 
are  unknown.  The  characteristic  feature  is  the  association  of 
the  oxides  of  iron  with  sulphides,  a  combination  practically  un- 
known in  fissure-veins,*  and  further  the  presence  of  various 
silicates  of  lime,  magnesia,  and  iron.  The  deposits  are  through- 
out metasomatic,  having  been  formed  by  the  replacement  of 
limestone;  and  the  filling  of  open  spaces  is  almost  entirely 
absent.  On  account  of  the  great  solubility  of  the  limestone, 
well-developed  crystals  of  the  gangue  minerals  are  very  com- 
mon. 

Exceptions. — There  are  some  classes  of  deposits  which, 
though  presenting  a  certain  similarity  to  this  type,  must  be 
strictly  separated  from  it.  Among  these  are  contact-deposits 
between  limestone  and  igneous  rocks  which  carry  as  metaso- 
matic products  (besides  galena  and  zincblende)  sericite,  dolo- 
mite, siderite  and  quartz,  and  which,  upon  close  investigation, 
are  usually  found  to  be  related  to  fissures  and  faults.  Further, 
certain  deposits  of  iron-ores,  associated  with  limestone  and  with 
garnet-pyroxene-amphibole  gangue,  but  without  any  apparent 

*  Specularite  and  arsenopyrite  are  both  known  from  cassiterite-veins,  which, 
however,  in  origin,  stand  close  to  pegmatite-veins  and  certain  contact- deposits. 


718       CHARACTER    AND    GENESIS    OF    CERTAIN    CONTACT-DEPOSITS. 

close  relation  to  intrusive  rocks.     This  kind  will  be  referred  to 
again  in  this  paper  in  the   discussion  of  the  genesis  of  the 

deposits. 

2.  Literature. 

Though  the  contact-deposits  here  described  are  not  very 
abundant,  and  rarely  of  great  economic  importance,  they  could 
not  long  escape  the  notice  of  mining  geologists.  In  1865 
B.  v.  Gotta*  described  the  celebrated  mines  of  the  Banat,  in 
Austria,  and  expressed  the  opinion  that  all  of  them  were  due 
to  the  action  of  intrusive  rocks  on  a  probably  Mesozoic  lime- 
stone. Regarding  some  of  these  deposits,  this  view  has  lately 
been  opposed  by  H.  Sj6gren,f  who,  however,  admits  that  others 
in  the  same  vicinity  may  stand  in  causal  relation  to  the  intru- 
sion. 

To  v.  Groddeck  belongs  the  credit  of  having  recognized 
these  deposits  as  a  separate  class,  J  which  he  calls  the  Kristi- 
ania  type,  and  characterizes  as  follows  : 

"  Siderite,  magnetite,  chalcopyrite,  bornite,  pyrite,  galena,  zincblende,  etc., 
accompanied  by  garnet,  ampkibole,  wollastonite,  axinite,  etc.,  mingled  in  very 
different  proportions,  forming  nests  and  stocks  at  the  contact  of  eruptive  rocks 
with  granular  limestone,  or  often  wholly  within  the  latter.  These  deposits  thus 
belong  in  the  sphere  of  contact-metamorphism,  and  may  be  briefly  characterized 
as  'contact-deposits.'  " 

Among  the  examples  are  mentioned  the  contact-deposits  of 
the  vicinity  of  Kristiania  and  those  in  the  Urals  (Bogoslowsk). 
Several  others  are  also  included  which  are  more  doubtful 
(Pyrenees,  Rodna,  Rezbanya,  Offenbanya,  the  Banat  and 
Schwarzenberg),  and  part  of  which  seem  to  be  due  to  regional 
metamorphism,  or  to  the  action  of  ascending  thermal  waters  at 
the  contact  of  lavas  and  limestone.  Y.  Groddeck  apparently 
fails  to  recognize  that  the  presence  of  intrusive  igneous  rocks  is 
necessary  to  develop  this  type  of  deposits.  Siderite,  mentioned 
in  his  definition  as  one  of  the  characteristic  minerals,  does  not 
occur  in  the  typical  examples,  and  seems  to  be  neither  common 
nor  essential. 

De   Launay§  also   describes    similar  deposits,  but  includes 

*  Erzlagerstatten  im  Banat  und  in  Serbien,  1865. 

f  Jahrbuchd.  K.  K.  Geol.  Reichsanstalt,  1886,  xxxvi.,  pp.  607-668. 

J  Die  Lehre  von  den  Lagerstatten  der  Erze,  1879,  p.  260. 

$  Traite  des  gites  metallifires,  Paris,  vol.  ii. ,  pp.  245-258. 


CHARACTER    AND    GENESIS    OF    CERTAIN    CONTACT-DEPOSITS.       719 

under  the  heading  several  other  deposits  not  so  clearly  belong- 
ing to  the  same  category,  and  hardly  recognizes  the  importance 
of  the  presence  of  intrusive  rocks.  In  addition  to  the  well- 
established  examples  from  v.  Groddeck,  de  Launay  adds  excel- 
lent descriptions  of  the  mines  of  Mednorudjansk  and  Ekater- 
inenbourg  in  the  Urals,  which  leave  little  doubt  that  these,  also, 
should  be  enrolled  under  the  Kristiania  type. 

In  Prof.  Kemp's  classification,*  the  following  division  is 
found  :  "  Contact-Deposits.  Igneous  rocks  always  form  one 
wall.  Fumaroles  (Greisen)."  This  is  evidently  to  include  several 
different  things  under  one  heading.  On  p.  222,  however,  Prof. 
Kemp  recognizes  the  importance  of  the  type  outlined  in  this 
paper,  one  example  of  which  is  mentioned,  namely,  that  of  the 
Seven  Devils  district,  Idaho.  Relating  to  the  same  subject  we 
find  (p.  69)  the  following  direct  utterance : 

11  In  the  more  characteristic  '  contact-deposits  '  the  igneous  rock  has  apparently 
been  a  strong  promoter  of  ore-bearing  solutions,  and  has  often  been  the  source  of 
the  metals  themselves.  This  form  of  deposit  becomes,  then,  an  attendant  phe- 
nomenon of,  or  even  a  variety  of,  contact-metamorphism." 

Prof.  Yogt  describes  contact  metamorphic  desposits  in  sev- 
eral of  his  recent  papers,  f  In  that  of  1894  the  contact-deposits 
near  Kristiania  are  described  on  the  basis  of  his  own  investiga- 
tions and  of  the  previous  work  of  Kjerulf.J  These  deposits, 
which  are  small  and  do  not  have  much  economical  importance, 
occur  in  the  majority  of  cases  exactly  on,  or  very  close  to,  the 
contact  of  syenitic  rocks  and  Silurian  limestone  and  slates, 
along  which  they  are  found  in  great  numbers  and  of  irregular 
form.  The  mineral  aggregates  sometimes  show  a  banding 
parallel  to  the  stratification,  and  are  only  found  in  the  sedi- 
mentary rock,  not  in  ..the  syenite.  The  gangue-minerals  are 
garnet,  amphibole,  pyroxene,  mica,  epidote,  vesuvianite,  scapo- 
lite,  chiastolite,  quartz,  calcite,  also  fluorite  and  axinite.  As 
ore-minerals  appear  magnetite,  hematite,  chalcopyrite,  galena, 
zincblende,  and,  more  rarely,  minerals  containing  bismuth, 
arsenic  and  antimony.  Besides  this  locality  are  mentioned 

*  Ore-Deposits  of  the  United  States  and  Canada,  J.  F.  Kemp,  3d  ed.,  p.  58. 

f  J.  H.  L.  Vogt.  Die  Kieslagerstatten  Roros-Sulitelma  und  Rammelsberg,  Z.  /. 
praJct.  Oeol.,  1891,  p.  177.  Zur  Classification  der  Erzvorkommen,  Z.  f.  prakt.  GeoL, 
1895,  p.  154.  Concentration  des  Metallgehaltes  zu  Erzlagerstalten,  Z.  f.  prakt.  GeoL , 
1898,  p.  416.  {  Udsigt  over  det  sydlige  Norges  Geologi,  Kristiania,  1879. 


720       CHARACTER    AND    GENESIS    OF    CERTAIN    CONTACT-DEPOSITS. 

others  from  the  Pyrenees,  Banat,  Pitkaranda  (Finland)  and 
Queensland. 

In  the  treatise  of  Phillips-Louis*  we  find  in  the  preliminary 
part  no  mention  of  this  type  of  contact>deposits ;  and,  in  the 
second  part,  giving  detailed  descriptions,  such  "  contact-depos- 
its "  as  Leadville,  Rodna  and  the  Banat  are  treated  together 
without  genetic  distinctions. 

3.   G-eogmphic  Distribution. 

Deposits  of  this  type  are  fairly  common  in  America,  though 
little  attention  has  been  directed  to  them,  probably  because  of 
their  smaller  economic  importance.  As  might  be  expected, 
most  of  them  are  found  in  the  regions  of  the  Pacific  Cordil- 
leras, where  great  intrusions  have  been  followed  by  uplifts  and 
enormous  erosion.  They  are  generally  found  at  the  contacts  of 
quartz-monzonites,  granodiorites,  quartz-diorites  and  diorites 
with  limestone.  Besides  the  gangue-minerals  mentioned 
above,  the  characteristic  ore-minerals  are  specularite  or  mag- 
netite with  bornite  or  chalcopyrite.  A  smaller  group  is  dis- 
tinguished by  the  additional  appearance  of  galena  and  zinc- 
blende  which,  in  places,  may  overshadow  the  copper  minerals 
in  economic  importance. 

California. — The  great  area  of  granodiorite  in  the  Sierra 
Nevada,  accompanied  by  smaller  areas  of  quartz-diorite,  breaks 
through  the  Paleozoic  and  Mesozoic  sedimentary  rocks.  Along 
the  contacts  thus  presented,  ore-deposits  of  the  type  here  de- 
scribed are  rarely  met  with,  perhaps  because  limestones  and 
calcareous  rocks  are  not  very  abundant.  However,  on  the  area 
of  the  Colfax  Folio  of  the  U.  S.  Geol.  Survey,  about  10  miles 
north  of  the  railroad  station  of  Emigrant  Gap,  Nevada  co.,  a 
mass  of  probably  carboniferous  limestone  has  been  greatly 
contact-metamorphosed  and  filled  with  garnets,  etc.,  but  no 
sulphides  appear  in  it.  Along  the  contacts  of  the  smaller  in- 
trusive areas  of  granodiorite  down  on  the  western  slope  of  the 
Sierra  Nevada  small  copper-deposits  are  occasionally  found. 
Near  Fairplay,  Eldorado  co.,  at  the  contact  of  granodiorite  and 
limestone  in  the  canon  of  the  Cosumnes  river,  garnets  and 
epidote  occur,  and,  intergrown  with  these,  small  masses  of 
bornite  and  chalcopyrite. 

*  A  Treatise  on  Ore-Deposits,  London,  1896. 


CHAKACTER    AND    GENESIS    OF    CERTAIN    CONTACT-DEPOSITS.       721 

In  Alpine  co.,  12  miles  due  south  of  the  southern  end  of 
Lake  Tahoe,  an  area  of  sedimentary  calcareous  rocks  of  uncer- 
tain (probably  Triassic)  age,  about  1.5  mile  long  and  0.5  mile 
wide,  occurs  embedded  in  granodiorite,  which  is  the  prevailing 
rock  in  that  vicinity.  The  locality  is  in  the  upper  part  of  Hope 
valley.  At  several  places  along  the  contacts,  mineralization 
has  taken  place.  The  prospects  were  visited  by  Mr.  H.  W. 
Turner  in  1888,  and  by  myself  in  1895.  At  Rodgers'  mine* 
the  strata  consist  of  alternating  thin  beds  of  quartzite  and  lime- 
stone, the  latter  carrying  the  principal  value.  The  ore-bearing 
strata  are  in  places  100  ft.  thick.  About  $100,000  worth  of 
ore  is  said  to  have  been  extracted  from  this  place  some  three  or 
four  decades  ago.  The  ore-minerals  consist  of  pyrrhotite, 
chalcopyrite  and  bornite,  and  contain  gold  as  well  as  some  sil- 
ver. The  principal  gangue-mineral  is  garnet. 

On  the  east  slope  of  Stevens  Peak,  in  the  same  area,  a 
stratum  of  limestone  near  the  contact  is  very  crystalline,  and 
contains  garnets  and  zincblende. 

At  Barnes'  prospect,  in  the  same  area,  a  wedge  of  limestone, 
projecting  into  the  surrounding  mass  of  granodiorite,  is  highly 
crystalline  and  filled  with  garnets,  amphibole,  and  other  con- 
tact-minerals. Of  ore-minerals,  magnetite  and  chalcopyrite  as 
well  as  bornite  were  found ;  these  are  reported  to  contain  some 
gold  and  silver. 

Idaho. — A  number  of  deposits  of  the  Kristiania  type  are  be- 
lieved to  occur  in  this  State,  though  their  true  nature  has 
rarely  been  recognized.  Position  and  mineral  association  indi- 
cate that  the  lead-zinc  deposits  at  South  Mountain,  Owyhee  co., 
are  true  contact-deposits,  though  when  visited  by  Mr.  F.  C. 
Schraderf  the  developments  did  not  permit  any  exact  study  of 
structural  relations.  The  ores  occur  on  the  contact  of  lime- 
stone and  diorite  or  granite ;  the  ore-minerals  are  argentiferous 
galena,  zincblende,  and  a  little  chalcopyrite  and  magnetite  ;  the 
gangue  being  garnet,  quartz,  actinolite  and  the  typical  contact- 
mineral  ilvaite  or  lievrite.  According  to  the  description  of  Mr. 
G-.  H.  Eldridge,{  certain  deposits  on  Sheep  Mountain  in  central 
Idaho  very  likely  belong  to  this  type. 

*  MS.  notes  by  Mr.  H.  W.  Turner. 

t  W.  Lindgren,  Silver  Oity  and  DeLamar,  20th  Ann.  Rep.  U.  S.  Geol.  Sur., 
Part  III.,  pp.  187-189.  J  16th  Ann.  Rep.  U.  S.  Geol  Sur.,  Part  II.,  p.  258. 


722       CHARACTER    AND    GENESIS    OF    CERTAIN    CONTACT-DEPOSITS. 

Most  characteristic  are  the   contact-deposits  of  the    Seven 
Devils,  briefly  described  in  a  recent  report.* 

In  the  Seven  Devils  district,  and  in  the  adjacent  Snake  River 
canon,  copper-deposits  are  very  abundant.  There  is,  in  that 
vicinity,  an  extensive  series  of  Triassic  basic  lavas,  with  inter- 
calated layers  of  slate  and  limestone.  There  are  also  diorites, 
intrusive  in  these  beds.  All  of  these  igneous  rocks  apparently 
contain  copper  which  was  easily  concentrated  into  deposits  of 
various  kinds ;  some,  fissure-veins;  others,  zones  of  impregna- 
tion ;  others,  contact-deposits.  In  the  locality  of  the  original 
discovery  in  the  Seven  Devils,  the  copper  occurs  in  typical 
contact-deposits.  Small  masses  of  limestones  are  embedded  in 
a  later,  intrusive  diorite;  at  the  contact,  and  usually  in  the 
limestone,  are  found  irregular  bodies  and  bunches  of  bornite, 
chalcocite,  and  a  little  chalcopyrite,  containing,  say,  10  oz.  of 
silver  and  a  little  gold  per  ton.  The  limestone  at  the  contact 
is  very  crystalline  and  contains,  associated  with  the  ores, 
abundant  garnet,  epidote,  quartz,  calcite  and  specularite.  The 
copper  sulphides,  as  shown  by  their  intergrowth,  were  certainly 
formed  at  the  same  time  as  the  gangue-minerals.  The  epidote, 
specularite  and  garnet,  as  described  by  Dr.  Palache,f  present 
clear  evidence  of  simultaneous  crystallization.  At  the  Peacock 
mine  a  large  body  of  medium-grade  ore  of  this  character  was 
embedded  in  diorite.  No  limestone  showed  here;  but  I  am 
informed  that  a  lower  tunnel  has  lately  encountered  limestone 
below  the  croppings. 

Other  claims  in  which  the  ore  occurs  on  the  contact  of 
limestone  and  diorite  are  the  "White  Monument,  Alaska, 
Blue  Jacket,  Helena  and  Decorah.  Considerable  masses  of 
ore  have  been  exposed  at  some  contacts,  though  the  distribu- 
tion is  extremely  irregular.  In  the  Blue  Jacket,  a  rich  body 
of  bornite  and  chalcocite  was  lately  found;  and  it  is  reported 
that  500  tons  of  40-per  cent,  ore  has  been  shipped  from  this 
mine  during  the  past  summer.  During  1900,  the  Boston  and 
Seven  Devils  Copper  Co.  shipped  from  the  Peacock  and  other 
claims  260  tons,  containing  23  per  cent,  of  copper,  besides  8 
oz.  of  silver  and  0.04  oz.  of  gold  per  ton. 

Still  another  copper  deposit  in  Idaho  which   appears  to  be- 

*  W.  Lindgren,  20th  Ann.  Eep.  U.  S.  Geol.  Sur.,  Part  III.,  p.  249. 
f  Am.  Jour.  Sci.,  3d  Sen,  vol.  viii.,  p.  299,  Oct.,  1899. 


CHARACTER    AND    GENESIS    OF    CERTAIN    CONTACT-DEPOSITS.       723 

long  to  this  type  is  the  "White  Knob  mine,  near  Houston,  in 
Lost  River  valley.  Mr.  W.  Darlington,  the  general  manager 
of  the  company,  has  kindly  furnished  the  following  informa- 
tion. The  ore  occurs  as  a  deposit  between  granite  and  lime- 
stone; the  trend  of  the  contact  is  1ST.  and  S.,  the  limestone 
lying  to  the  E.  and  the  granite  to  the  W.  On  the  surface  the 
ore-bearing  zone  is  1200  ft.  in  length,  and  (as  a  maximum)  400 
ft.  in  width.  The  minerals  are  hematite,  magnetite,  chalcopy- 
rite,  pyrite  and  a  little  galena,  in  a  gangue  of  garnet  and 
coarsely  crystalline  calcite.  A  porphyry  dike  also  occurs  on 
the  contact,  complicating  the  geological  relations.  The  oxi- 
dized zone  is  very  deep,  water  not  having  been  encountered 
until  the  depth  of  600  ft.  was  reached  in  the  shaft. 

Arizona. — It  is  well  known  that  many  and  very  important 
copper-deposits  occur  associated  with  limestone  and  igneous 
rocks  in  Arizona.  The  descriptions  published  seem  to  indicate 
that  few  of  them,  if  any,  are  contact-deposits  of  the  Kristiania 
type.  In  most  of  them,  also,  the  zone  of  oxidation  is  very  deep 
and  their  original  character  has  been  greatly  altered. 

British  Columbia. — Recent  literature  describing  the  copper- 
deposits  of  Vancouver  and  Texada  islands  points  without  doubt 
to  the  existence  of  numerous  and  important  contact-deposits  in 
those  localities.  Already  indicated  by  Mr.  Carlyle,*  this  is 
confirmed  by  Mr.  "Wm.  M.  Brewerf.  The  deposits  always 
occur  in  or  very  near  the  contacts  between  limestone  and  gab- 
bro  or  diorite.  The  mineral  association  is  magnetite,  chalcopy- 
rite,  hornblende  and  garnet.  In  some  places  the  magnetite 
predominates,  almost  to  the  exclusion  of  the  chalcopyrite. 

Northwest  Territory* — Mr.  R.  H.  Stretch  has  recently  de- 
scribed;); interesting  deposits  on  the  Upper  Yukon,  which,  to 
judge  from  the  excellently  presented  data,  are  contact-deposits 
of  the  Kristiania  type.  Mr.  Stretch,  however,  it  is  fair  to  say, 
does  not  consider  them  as  due  to  contact-metamorphic  origin, 
but  as  a  result  of  later  mineralization:  The  locality  is  a  few 
miles  west  of  White  Horse  Rapids,  lat.  60°  40',  long.  135°. 

The  prospects  are  found  along  a  narrow  strip  at  the  base  of 

*  Report  of  the  Provincial  Mineralogist,  1897. 

f  The  Copper-Deposits  of  Vancouver  Island.    Trans.,  xxix.,  483.    Eng.  &  Mm. 
Jour.,  1900,  Apr.  21,  May  5,  July  14. 

J  Eng.  &  Min.  Jour.,  Sept.  8,  1900.     Notes  on  the  White  Horse  Copper-Belt. 

46 


724      CHARACTER    AND    GENESIS    OF    CERTAIN    CONTACT-DEPOSITS. 

a  mountain  range,  consisting  chiefly  of  limestone.  This  base 
is  a  granite  plateau  which  Mr.  Stretch  thinks  underlies  lime- 
stone ;  in  fact,  a  few  patches  of  limestone  remain  on  the  plateau. 
The  ores  occur  at  the  contact  of  the  two  rocks,  or  in  seams  of 
varying  size  in  the  granite.  Two  classes  of  ores  are  found : 
(1)  large  masses  of  specularite  or  magnetite,  carrying  a  moder- 
ate amount  of  copper  ;  (2)  outcrops  of  smaller  dimensions,  in 
which  the  ore  is  bornite  with  a  little  chalcopyrite.  Many  of 
these  prove  to  be  connected  with  E.— W.  seams  penetrating  the 
granite,  but  nowhere  show  evidence  of  massive  vein-structure. 

At  all  the  localities,  epidote  and  lime-garnets  are  present.  The 
bornite  contains  some  gold  and  silver ;  and  a  little  molybdenite 
is  also  found.  Dikes  of  granite  occasionally  cut  the  limestone. 

Mexico. — From  a  perusal  of  recent  geological  literature  of 
Mexico,  it  is  clear  that  contact-deposits  of  the  Kristiania  type 
are  very  abundant  there — more  so  than  in  other  parts  of  JsTorth 
America.  In  a  review  of  the  gold-deposits  of  the  republic, 
Mr.  Ordonez*  says : 

' '  Examples  of  another  type  of  ore-deposits  are  found  in  regions  where  sedi- 
mentary Mesozoic  rocks  appear,  that  is,  on  the  eastern  slopes  of  the  Sierra  Madre, 
towards  the  Gulf  of  Mexico.  These  consist  of  contact-veins  between  generally 
Cretaceous  limestones  and  eruptive  granitic  rocks,  nearly  always  diorite.  The  lime- 
stones are  metamorphosed  at  the  contact,  and  the  copper  minerals  containing 
gold  occur  irregularly  distributed  in  contact-metamorphic  silicates,  such  as  gar- 
net and  epidote. 

u  Such  deposits  exist  at  Encarnacion,  district  of  Zimapan,  also  in  the  vicinity 
of  San  Jose'  del  Oro  ;  further,  at  San  Jose",  Central  district,  State  of  Tamauli- 
pas,  as  well  as  at  many  other  places." 

Aguilera  and  Ordonez,  mentioning  several  localities  in  their 
sketch  of  the  Geology  of  Mexico,  f  write  as  follows  : 

1 '  In  the  region  of  Mazapil,  Zacatecas,  an  extensive  formation  of  Cretaceous 
limestone  is  cut  by  dioritic  rocks.  Near  the  contact  extend  very  important  de- 
posits, worked  during  many  years.  The  contact  is  marked  by  a  conversion  of  the 
limestone  to  marble." 

"  Chalcopyrite,  always  accompanied  by  grossularite  (garnet),  and  usually  by 
hematite,  occurs  in  Cretaceous  limestone,  and  its  appearance  is  due  to  the  eruption 
of  igneous  rocks,  as  may  be  seen  at  San  Jose"  in  the  Sierra  San  Carlos,  in  Ta- 
maulipas,  in  which  copper-minerals,  accompanied  by  magnetite,  appear  at  the 
contact  of  the  andesitic  diorite." 

*  Note  sur  les  gisements  d'or  du  Mexique,  Mexico,  1898,  p.  233. 
f  Sosquejo  geologico  de  Mexico,  Mexico,  1897,  pp.  68,  222.     JBoletin  del  Institute 
geol.  de  Mexico,  Nos.  4,  5,  6. 


CHARACTER    AND    GENESIS    OF    CERTAIN    CONTACT-DEPOSITS.       725 

A  similar  deposit  from  the  State  of  Chiapas  is  interestingly 
described  by  Mr.  E.  T.  McCarty.*  Here  limestone  of  unknown 
age  is  invaded  from  below  by  rocks  called  trap,  syenite  or 
dolerite.  At  the  contacts  the  limestone  is  largely  converted 
into  wollastonite  and  garnet,  besides  a  little  quartz,  chalcedony, 
calcite  and  aragonite.  This  contact-metamorphosed  limestone 
contains,  partly  scattered  through  it,  partly  in  more  concen- 
trated but  very  irregular  "  ore-channels,"  auriferous  and  argen- 
tiferous bornite,  as  well  as  some  chalcopyrite,  enargite,  galena 
and  linnseite.  The  average  ore  consists  of  90  per  cent,  of  gar- 
net with  10  per  cent,  of  quartz  and  chalcedony,  carrying  from  3 
to  4  per  cent,  of  copper  and  from  6  to  8  oz.  silver,  and  from  $6 
to  $20  in  gold,  per  ton.  The  gold  is  in  part  free  and  visible. 
Regarded  as  a  whole,  the  ores  appear  in  curved  planes,  which 
probably  follow  the  outline  of  the  underlying  intrusive.  The 
total  width  of  the  ore-bearing  limestone  is  about  30  ft.,  and 
within  this  distance  are  two  ore-bearing  streaks.  Very  often 
the  ore  lies  directly  on  the  contact. 

Other  Countries. — In  the  foregoing  brief  notes  I  have  at- 
tempted to  call  attention  to  the  occurrences  of  this  type  in 
America  only.  But  short  and  incomplete  descriptions,  found 
here  and  there  in  the  literature  of  the  subject,  make  it  more 
than  likely  that  such  contact-deposits  occur  in  West  Australia, 
Queensland,  South  Africa  and  China.  From  the  latter  country, 
for  instance,  F.  L.  Garrisonf  describes  lead-  and  zinc-deposits 
in  contact-metamorphic  limestone,  near  granite. 

II. — ORIGIN  OF  THE  DEPOSITS. 

The  deposits  of  the  Kristiania  type  may  be  separated  into 
several  subdivisions,  according  to  the  prevalence .  of  certain 
metallic  minerals.  Thus  we  have  iron-deposits,  carrying 
chiefly  magnetite  and  specularite;  copper-deposits,  characterized 
by  bornite  and  chalcopyrite;  and  finally  zinc-lead  deposits, 
containing  galena  and  zincblende.  These  three  groups  are 
connected  by  transitional  examples.  In  all  of  them  the  metallic- 

*  "Mining  in  the  Wollastonite  Ore-Deposits  of  the  Santa  F6  Mine,  Chiapas, 
Mexico,"  Trans.  Inst.  Min.  and  Met.,  London.,  vol.  iv.,  pp.  169-189  (1895- 
1896).  See  also  H.  F.  Collins,  Id.,  Feb.,  1900;  and  Mr.  Collins's  "Note  on 
Cheap  Gold' Milling  in  Mexico,"  in  Trans.,  xxi.,  446. 

f  Mining  and  Metallurgy,  Feb.  15,  1891,  p.  107. 


726      CHARACTER   AND    GENESIS    OF    CERTAIN   CONTACT-DEPOSITS. 

minerals  are  intergrown  with  the  various  gangue-minerals, — 
garnet,  epidote,  wollastonite,  etc. — in  such  a  manner  that  they 
must  be  considered  as  having  a  simultaneous  origin.  The  the- 
ory of  a  subsequent  introduction  of  the  metallic  ores  is  decid- 
edly untenable.  Since,  on  the  other  hand,  the  garnets  and  other 
gangue-minerals  stand  in  unquestionable  relation  to  the  contact- 
metamorphic  action,  a  theory  of  the  origin  of  these  deposits 
certainly  becomes  a  branch  of  the  study  of  contact-metamor- 
phism. 

1.   Contact-MetamorpUsm. 

The  peculiar  action  of  intrusive  igneous  bodies  upon  ad- 
jacent sedimentary  rocks  is  a  well-known  fact  in  geology  and 
petrography.  The  sedimentaries  usually  suffer  a  more  or  less 
intense  metasomatic  alteration,  termed  contact-metamorphism. 
Surface-eruptions  (lavas),  as  a  rule,  exert  no  such  intense  action, 
though  a  certain  baking  or  partial  melting  of  the  immediately 
adjoining  rock  may  sometimes  be  recognized.  The  metamor- 
phism  exerted  by  intrusive  rocks  is  characterized  by  a  gradu- 
ally fading  alteration  of  the  sediments,  sometimes  extending 
over  a  width  of  several  kilometers.  The  contact  of  the  altered 
rocks  with  the  intrusive  is  usually  sharp,  a  melting  of  the 
former  being  rarely  if  ever  noticed.  Slates  and  shales  in  the 
immediate  vicinity  of  the  intrusive  rock  are  changed  to  highly 
crystalline  schists  or  massive  crystalline  rocks,  containing  an- 
dalusite,  feldspar,  cordierite,  garnets,  etc. ;  further  away, 
slighter  recrystallization  results,  with  development  of  mica 
and  accumulation  of  the  carbon  of  the  shales  in  little  knots 
and  masses.  In  general,  there  is  no  considerable  addition  or 
subtraction  of  material  during  the  metamorphism.  Limestone 
usually  suffers  a  stronger  contact-metamorphism  and  becomes 
a  coarse-grained  marble.  Garnet,  wollastonite,  amphibole, 
pyroxene,  epidote,  etc.,  often  well  crystallized  in  large  indi- 
viduals, form  in  it.  In  this  case  there  is  usually  an  addition 
of  silica  and  a  loss  of  carbon  dioxide.  In  many  places  the 
contact-zone  has  received  an  access  of  certain  minerals  con- 
taining boron  and  fluorine  not  contained  in  the  unaltered 
rocks ;  the  most  common  of  these  are  tourmaline  and  topaz. 
Oxides  and  sulphides,  such  as  magnetite,  specularite,  ilmenite, 
pyrite  and  pyrrhotite,  are  often  contained  in  contact-metamor- 


CHARACTER    AND    GENESIS    OF    CERTAIN    CONTACT-DEPOSITS.       727 

phic  slates  and  schists.*  Magnetite,  pyrite  and  pyrrhotite 
have  been  observed  in  limestones  (Morbihan,  France)  ;f  and  the 
Devonian  limestones  at  Rothau,  in  the  Vosges,  are  metamor- 
phosed for  a  few  hundred  feet  from  the  contact,  and  contain 
pyroxene,  garnet,  epidote  and  a  little  galena.  J 

Brogger,  in  his  studies  of  the  contact-metamorphic  rocks 
near  Kristiania,§  remarks: 

' '  Pyrrhotite  appears  abundantly  in  the  altered  rocks,  and  is  certainly  a  mineral 
formed  during  the  contact-metamorphism,  for  it  does  not  occur  in  the  unaltered 
rocks.  It  is  not  easy  to  say  whether  an  addition  of  material  has  really  taken 
place,  or  the  mineral  represents  a  r  eery  stall  izati  on  of  finely  distributed  pyrite. 
Strongly  in  favor  of  the  hypothesis  of  direct  addition  is  the  fact  that  large  accu- 
mulations of  pyrrhotite  exist  in  the  contact-metamorphic  rocks — so  large,  indeed, 
that  mining  has  been  attempted  in  places."  .  ...  "As  already  indicated  by 
Kjerulf,  we  must  consider  the  many  small  ore-deposits  occurring  along  the  con- 
tacts of  granite  and  syenite  with  Silurian  rocks  as  contact-formations  ;  and  they 
should  really  be  included  in  any  study  of  the  contact-metamorphism  of  this 
region." 

The  same  opinion  is  strongly  held  by  Prof.  Vogt. 

Cause  of  Contact- Metamorphism. — Petrographers  in  general 
agree  that  contact-metamorphism  is  due  to  the  heat  of  the 
molten  magma  combined  with  the  action  of  the  water  which 
it  contains.  It  is  well  known  that  during  and  following  vol- 
canic eruptions,  water,  hydrogen  sulphide,  sulphur  dioxide 
and  carbon  dioxide,  as  well  as  compounds  of  chlorine,  fluorine 
and  boron,  are  emitted.  While  some  of  these  may  result  from 
the  contact  of  the  lavas,  with  water  and  other  materials,  which 
they  encounter  at  their  eruption,  it  is  extremely  probable  that 
a  large  proportion  of  them  is  derived  from  the  magmas  them- 
selves. ||  This  opinion  is  supported  by  excellent  geological 
authority — for  instance,  by  Prof.  T.  C.  Chamberlin,  who  says  :f 

"  It  is  a  familiar  fact  that  enormous  quantities  of  gases  are  ejected  from  volca- 
noes. It  has  been  assumed  that  these  have  a  surface-origin,  and  this  is  true  in 
part;  but,  on  the  other  hand,  there  is  abundant  ground  for  the  belief  that  another 
notable  part  is  brought  from  the  interior,  and  is  a  real  contribution  to  the  earth's 
atmosphere  and  hydrosphere." 

This  is  confirmed  by  the  well-known  fact  that  deep-seated 

*  F.  Zirkel,  Lehrbuch  der  Petrographie,  Leipzig,  1894,  ii.,  p.  97. 

f  Loc.  cit.,  p.  113.  J  Loc.  cit.,  p.  115. 

§  Die  Silurischen  Etagen,  2  and  3.     Kristiania,  1882,  p.  369. 

||  Braun's   Chemische  Mineralogie,  Leipzig,  1896,  pp.  283-287. 

If  Jour,  of  GeoL,  vii.,  p.  559,  1899.     (Quotation  slightly  condensed. ) 


728       CHARACTER    AND    GENESIS    OF    CERTAIN    CONTACT-DEPOSITS. 

igneous  rocks  contain  much  carbon  dioxide,  and  also,  some- 
times, sulphides ;  while  both  are  much  less  common  in  extru- 
sive lavas. 

No  matter  by  what  force,  the  igneous  rocks  have  certainly 
been  brought  up  from  deeper  levels.  If  we  admit  that  they 
contained  dissolved  various  substances,  such  as  water,  carbon 
dioxide,  and  compounds  of  sulphur,  chlorine,  boron  and  flu- 
orine, with  various'  metals,  it  follows  that  the  diminution  of 
pressure  caused  by  the  rise  to  higher  levels  will  gradually  re- 
sult in  the  escape  of  these  compounds,  which  are  so  much  more 
volatile  than  the  other  constituents  of  the  magma.  The  higher 
the  rise  of  the  magma,  the  more  complete  the  liberation  of 
these  substances.  In  what  form  they  will  escape,  depends  on 
the  critical  temperature  of  the  substances  and  the  pressure  at 
the  point  of  issue.  We  may  assume  with  great  confidence  that 
at  the  contacts  of  intrusive  rocks  with  a  sedimentary  series  the 
temperature  usually  exceeded  365°  C.  and  the  pressure  200 
atmospheres.  Under  these  conditions  the  water,  and  likewise 
most  of  the  more  or  less  volatile  compounds  mentioned,  would 
exist  as  a  gas ;  in  other  words,  pneumatolytic  conditions  would 
prevail.  The  water  and  accompanying  compounds  would  be 
released  from  the  magma  and  would  penetrate,  more  or  less 
energetically,  the  adjoining  rocks  for  a  varying  distance.  It 
does  not  seem  probable  that  atmospheric  water  could  have 
gained  access  to  the  contacts  during  the  period  of  consolida- 
tion. Both  the  heat  of  the  igneous  rock  and  the  pressure  of 
the  volatile  compounds,  striving  to  free  themselves  from  the 
association  with  the  magma,  would  prevent  this. 

The  escape  of  the  gases  may  be  facilitated  by  cracks  and 
fissures,  and  the  emanations  may  be  gradually  taken  up  by 
circulating  surface-water,  which  then  will  appear  as  thermal 
springs.  Among  the  supporters  of  this  view  may  be  mentioned 
Profs.  Rosenbusch*  and  Chamberlin.f 

Admitting  the  tendency  of  the  more  volatile  constituents  of 
the  magma  to  leave  it  under  relaxing  pressure,  and  knowing 
the  tendency  of  the  "  mineralizing  agents "  to  form  volatile 
compounds  with  various  metals,  it  does  not  seem  so  very  sur- 
prising that  mineral-deposits  of  various  kinds  should  be  formed 

*  Elemente  der  Oesteinslehre,  Stuttgart,  1898,  p.  42.  f  LOG.  dt.,  p.  559. 


CHARACTER    AND    GENESIS    OF    CERTAIN    CONTACT-DEPOSITS.       729 

during  the  contact-metamorphism.  The  only  thing  needed  is 
a  substance  causing  their  deposition,  and  thus  preventing  their 
escape  to  join  the  circulating  surface-waters.  Such  a  substance 
is  limestone.  A  chemical  reaction  appears  to  take  place  be- 
tween the  substances  leaving  the  magma  and  the  carbonate 
of  lime,  causing  the  deposition  of  new  minerals  and  the  libera- 
tion of  carbon  dioxide. 

To  some  degree,  this  is  confirmed  by  the  experiment  of 
Senarmont,*  who  obtained  crystallized  specularite  by  pro- 
longed action  of  a  solution  of  ferric  chloride  on  calcium  carbon- 
ate, at  300°  C.,  in  a  closed  tube.  Further  experimental  tests  in 
this  direction  would  be  most  desirable.  Also  interesting  and 
pertinent  to  this  question  is  the  experiment  of  Doelter,f  who 
obtained  magnetite  by  cooling  limestone  in  molten  basaltic 
rock ;  this  magnetite  was  clearly  derived  from  the  basalt,  and 
was  found  segregated  on  the  contact. 

The  genesis  of  the  contact-deposits  of  the  Kristiania  type 
thus  seems  to  be  due  to  aqueous  gas  above  the  critical  tempera- 
ture, which  was  more  or  less  laden  with  metallic  compounds, 
and,  under  heavy  pressure,  penetrated  the  limestone  adjacent 
to  the  igneous  intrusive  body.  The  temperatures  must  have 
been  very  high,  but  generally  below  the  melting-point  of  ordi- 
nary rocks.  Carbon-  dioxide  was  evidently  not  an  active  re- 
agent ;  for  the  principal  reaction  consists  in  its  expulsion  from 
the  limestone.  Under  the  prevailing  conditions,  the  metals  can- 
not reasonably  be  supposed  to  have  been  derived  from  the  lime- 
stone. Everything  points  to  the  conclusion  that  the  metallic 
substances  were  given  off  by  the  cooling  magma. 

This  is  also,  in  general,  the  conclusion  of  all  who  have  care- 
fully examined  these  deposits,  from  v.  Cotta  and  v.  Groddeck 
to  Prof.  Vogt,  who  has  more  recently  written  on  the  subject.^ 

The  ores  were  deposited  during  the  consolidation  of  the 
magma.  The  larger  part  of  them  occur  in  the  limestone ;  but 
it  is  not  inconsistent  with  the  theory  here  developed  that  some 
ore  may  also  be  occasionally  found  in  the  adjacent  igneous 
rock.  The  deposits  are  entirely  metasomatic.  The  ore  and 
gangue  replaced  limestone  ;  and  there  were,  as  a  rule,  no  open 
cavities  to  be  filled. 

*  Braun's  Chemische  Mineralogie,  Leipzig,  1896,  p.  268.         f  Loc.  cit.,  p.  253. 
J  Z.f.  prakt.  QeoL,  1898,  p.  416. 


730      CHARACTER   AND    GENESIS    OF   CERTAIN    CONTACT-DEPOSITS. 

2.  Similar  Deposits  of  Different  Origin. 

As  mentioned  before,  there  are  certain  deposits  which  owe 
their  origin  to  dynamo-metamorphic  or  N  regional-metamorphic 
processes,  and  which  show  a  considerable  similarity  to  the 
Kristiania  type.  Indeed,  the  minerals  of  regional-metamor- 
phism  are  generally  identical  with  those  of  contact-metamor- 
phism,  and  the  agencies  are  evidently  similar.*  We  may  sup- 
pose that  in  the  latter  case  they  consisted  of  water  under  con- 
siderable pressure  and  at  a  fairly  high  temperature ;  but  it  does 
not  seem  at  all  likely  that  the  conditions  were  pneumatolytic, 
or  that  the  temperature  approached  that  of  the  intrusive  con- 
tacts. Characteristic  for  the  regional-metamorphic  deposits  are 
(1)  the  association  of  oxides  of  iron  with  sulphides  so  utterly 
foreign  to  the  deposits  formed  by  ascending  waters,  and  (2)  the 
minerals  (garnet,  amphibole,  epidote,  etc.)  which  distinguish 
the  contact-deposits.  Bornite,  so  common  in  the  latter,  does 
not,  however,  seem  to  occur  in  regional-metamorphic  deposits. 
In  regional-metamorphism  there  has  been  but  little  transporta- 
tion of  substance ;  the  masses  of  ore  are  rather  old  dissemina- 
tions, or  originally  sedimentary  deposits,  concentrated  and  re- 
arranged under  the  influence  of  heat  and  permeating  moisture. 
As  examples  of  deposits  of  regional-metamorphic  origin  may 
be  mentioned  the  principal  iron-ore  deposits  of  Sweden  and 
those  of  Michigan. 

3.   Genetic  Classification. 

The  form  of  mineral  deposits  is  sometimes  characteristic,  but 
at  no  time  essential.  Hydrothermal  deposits  are  usually  tabular, 
but  this  is  only  because  ascending  hot  waters  usually  find  it 
convenient  to  follow  the  easy  path  of  open  fissures. 

It  seems  appropriate  to  make  a  separate  division  into  hydro- 
thermal  deposits  caused  by  hot,  ascending  waters,  and  character- 
ized by  certain  very  diversified,  but  still  similar,  metasomatic 
alteration,  which  I  have  elsewhere  described  more  in  detail. f 
No  doubt  these  will  be  found  to  merge  gradually  into  the 
deposits  caused  entirely  by  cold  surface-waters. 

A  second  division  should  be  made  to  include  "  contact-meta- 
morphic  "  deposits,  wholly  differing  in  mineral  association  and 

*  See,  for  instance,  C.  K.  Van  Hise,  Bull  Geol.  Soc.  Am.,  vol.  ix.,  p.  311. 
f  "  Metasomatic  Processes  in  Fissure- Veins,"  this  volume,  p.  498. 


CHARACTER    AND    GENESIS    OF    CERTAIN    CONTACT-DEPOSITS.       731 

metasomatic  character  from  the  first  division.  Between  the 
two  divisions,  but  more  closely  related  to  the  hydrothermal 
class,  stand  the  cassiterite  veins.  A  third  division  may  be 
made  to  include  the  dynamo-metamorphic  and  regional-metamorphic 
deposits,  similar  to  the  contact-deposits  in  mineral  association, 
but  chiefly  consisting  of  concentrated  old  impregnations,  or  old 
sedimentary-deposits  enriched  by  metasomatic  processes,  very 
different  from  those  caused  by  the  strong  solutions  of  hydro- 
thermal  waters.  Transitions  are  to  be  found,  no  doubt,  between 
the  hydrothermal  and  the  dynamo-metamorphic  deposits,  but 
this  does  not  diminish  the  value  of  these  principal  divisions. 
It  is  worthy  of  note  that  a  very  large  proportion  of  the  total  pro- 
duction of  gold  and  silver  is  derived  from  hydrothermal  deposits. 
Prof.  Van  Hise  has  recently,  in  a  most  instructive  and  inter- 
esting paper,*  suggested  a  classification  in  which,  at  first  glance, 
there  would  seem  to  be  no  place  left  for  deposits  of  the  kind 
here  described.  It  is  probable,  however,  he  did  not  intend  to 
limit  the  "  igneous "  deposits  to  those  consolidated  from  a 
molten  magma,  as  might  be  inferred  from  his  paper  (Trans., 
xxx.,  pp.  30-177),  for  on  page  174  is  the  following  statement : 

"  I  even  hold  that  there  are  gradations  between  ore-deposits  which  may  be  ex- 
plained wholly  by  igneous  agencies  and  those  which  may  be  explained  wholly  by 
the  work  of  underground  water." 

From  other  papers  it  is  also  clear  that  Prof.  Van  Hise  admits 
that  emanations  from  intrusive  magmas  may  mingle  with  the 
waters  of  atmospheric  origin,  and  that  deposits  may  be  formed 
in  this  way ;  for  he  saysf  that 

"  It  is  thought  highly  probable  that  under  sufficient  pressure  and  at  a  high 
temperature  there  are  all  gradations  between  heated  waters  containing  mineral 
material  in  solution  and  a  magma  containing  water  in  solution.  ...  If  this  be 
so,  there  will  be  all  stages  of  gradation  between  true  igneous  injection  and  aque- 
ous cementation,  and  all  the  various  phases  of  pegmatization  may  thus  be  fully 
explained." 

In  the  succeeding  paragraph  in  the  same  paper,  observations 
in  the  Black  Hills  of  Dakota  are  recorded,  which  appear  to 
show  that  a  regular  transition  exists,  from  pegmatitic  veins  to 
normal  quartz-veins,  the  latter  appearing  furthest  away  from 
the  igneous  core  which  furnished  the  material  for  the  pegmatitic 
veins. 

*  "Some  Principles  Controlling  the  Deposition  of  Ores,"  Trans.,  xxx.,  27. 
f  16th  Ann.  Rept.  U.  S.  Geol.  Sur.,  Part  I.,  p.  687. 


732       CHARACTER    AND    GENESIS    OF    CERTAIN    CONTACT-DEPOSITS. 

4.  Relation  of  Pegmatite-  Veins  to  Ore-Deposits. 

The  pegmatite-veins  contain  coarse  granular  aggregates  of 
quartz  and  feldspar  usually  characterized  by  simultaneous  crys- 
tallization; associated  with  these  are  a  great  number  of  rarer 
minerals,  such  as  zircon,  apatite,  specularite,  tourmaline,  topaz, 
beryl,  and  a  vast  number  of  minerals  containing  the  rare  earths. 
Their  origin  has  for  a  long  time  been  a  subject  for  discussion, 
both  consolidation  from  a  molten  magma  and  aqueous  deposition 
being  suggested.  The  modern  view  of  their  genesis,  represented 
by  Messrs.  Brogger  and  Rosenbusch,  is  that,  while  they  may  be 
to  some  extent  the  result  of  consolidation  from  a  molten  state, 
they  are  very  largely  of  pneumatolytic  origin. 

The  pegmatite-veins  are  formed  after  the  consolidation  of  the 
main  mass  of  the  igneous  rock,  and  are  to  be  considered  as  the 
last  results  of  magmatic  differentiation.  That  they  are  so  much 
richer  in  the  rarer  minerals  than  the  igneous  rock  with  which 
they  are  associated,  is  to  be  explained  by  the  concentration  of 
the  escaping  volatile  compounds  of  boron,  chlorine,  fluorine  and 
sulphur  into  a  smaller  volume  of  residual  magma.*  A  migra- 
tion of  these  volatile  compounds  into  the  surrounding  rock  may 
sometimes  be  noted.  Thus,  for  instance,  Prof.  Patton  describes,! 
from  Colorado,  tourmaline  impregnating  schist  for  2  or  3  ft.  on 
both  sides  of  a  10-ft.  pegmatite- vein,  which  itself  only  carries 
a  smaller  percentage  of  that  mineral. 

Sulphides,  as  well  as  oxides,  are  sometimes  found  in  pegma- 
tite-veins, though  I  know  of  no  instance  of  economically  valu- 
able masses.  Among  the  minerals  are  cassiterite,  wolframite, 
specularite,  lollingite  (FeAs2),  molybdenite,  zincblende,  galena 
and  chalcopyrite.  At  least  one  of  these,  lollingite,  Brogger  re- 
gards as  certainly  belonging  to  the  earliest  period  of  pegmatite 
formation  (magmatic  consolidation,  accompanied  by  pneumato- 
lytic action) ;  while  others  are  regarded  to  have  been  formed 
by  a  combination  of  pneumatolytic  and  aqueous  agencies. 

It  has  been  noted  that  many  pegmatite-veins  are  exception- 
ally rich  in  quartz,  and  it  has  been  suggested  that  normal 
quartz-veins  may  form  transitions  into  pegmatite-veins.  Occur- 
rences apparently  confirming  this  view  have  been  recorded  by 

*  W.   C.  Brogger,  Die  Mineralien  der  Sildnorwegischen  Pegmatitgange,  Zschr.  f. 
Kryst.  und  Min.,  Bd.  xvi.,  p.  213. 
t  Bull  Geol.  Soc.  Am.,  vol.  x.,  pp.  21-26,  1899. 


CHARACTER    AND    GENESIS    OF    CERTAIN    CONTACT-DEPOSITS.       733 

many  reliable  observers,  such  as  G.  H.  Williams,*  Van  Hise,f 
Crosby,J  Fuller  and  Spurr.§  Mr.  Spurr  explicitly  declares  his 
belief  that,  in  the  Yukon  district,  pegmatite-veins  form  transi- 
tions into  gold-bearing  quartz-veins;  these  latter,  he  thinks, 
have  been  "  deposited  from  (magmatic)  solutions  so  attenuated 
that  they  may  best  be  described  as  waters  highly  heated  and 
heavily  charged  with  mineral  matter  in  solution." 

These  observations  are  highly  interesting.  It  is  quite  pos- 
sible that  some  such  relation  exists  between  pegmatite-  and 
quartz-veins.  But  it  must  be  strongly  emphasized  that  the 
descriptions  of  such  transitions  should  be  fully  proved  by  series 
of  exact  assays.  This  has  not  yet  been  done.  It  is  possible, 
of  course,  that  the  vertical  distance  between  pegmatites  and 
normal  gold-quartz  veins  may  be  so  great  that  transitions  be- 
tween them  could  not  ordinarily  be  studied  in  any  one  dis- 
trict ;  or  it  may  be  that,  if  some  of  the  gold  in  quartz-veins  has 
been  derived  by  exhalations  from  a  congealing  magma,  it  was 
carried  off  by  other  agencies  than  the  pegmatite-veins.  Against 
the  suggested  relationship  speaks  the  fact  that  California,  Idaho 
and  Oregon  gold-quartz  veins  show  no  relation  whatever  to 
pegmatitic  dikes ;  also,  the  conditions  observed  in  North  Caro- 
lina, where  Pratt ||  describes  normal  auriferous  quartz-veins, 
occurring  together  with  barren  lenses  of  pegmatitic  quartz. 
The  subject  is  attractive,  and  well  worthy  of  further  investiga- 
tion. 

NOTE. — Since  this  paper  was  written  I  have  had  opportunity 
to  read  Prof.  Yogt's  most  interesting  contribution,  "Problems 
in  the  Geology  of  Ore-Deposits. "1f  This,  to  a  most  desirable  de- 
gree, confirms  and  completes  the  necessarily  abbreviated  state- 
ments in  these  notes,  while  its  scope  is  very  much  larger.  The 
pyritic  deposits  of  the  type  Rio  Tinto,  Rammelsberg  and  Roros, 
which  Prof.  Vogt  includes  under  the  heading  of  contact-meta- 
m orphic  origin,  I  have  not  attempted  to  discuss,  on  account  of 
my  very  limited  acquaintance  with  them. 

*  15th  Ann.  Rept.  U.  S.  Geol.  Sur.,  p.  678. 

f  16^  Ann.  Rept.  U.  S.  Geol.  Sur.,  Parti.,  p.  687. 

J  Amer.  Geologist,  xix.,  p.  147. 

%  18th  Ann.  Rept.  U.  S.  Geol.  Sur.,  Part  III.,  p.  312. 

||  Mining  and  Metallurgy,  Feb.  15,  1901,  p.  108. 

fl  See  page  636  of  the  present  volume. 


734  THE    FORMATION    OF    BONANZAS    IN    GOLD-VEINS. 


The  Formation  of  Bonanzas  in  the  Upper  Portions  of 

Gold- Veins. 

BY  T.   A.    RICKARD,    DENVER,    COLORADO. 

(Richmond  Meeting,  February,  1901.) 

INTRODUCTORY. 

THE  presentation  to  the  Institute,  eight  years  ago,  of  the  paper 
of  Posepny  on  "  The  Genesis  of  Ore-Deposits  "  has  home  fruit 
in  much  fresh  investigation,  as  is  evidenced,  for  example,  hy 
the  group  of  very  valuable  papers,  hy  distinguished  members 
of  the  United  States  Geological  Survey,  read  at  the  Washing- 
ton meeting — discussions  of  general  principles  particularly  sug- 
gestive to  those  who  are  engaged  in  mining. 

Posepny,  in  the  discussion  of  his  famous  treatise,  said  that 
the  present  writer  seemed  to  look  at  every  new  conception  in 
ore-deposition  "  from  the  sole  standpoint  of  its  immediate  use- 
fulness in  mining."*  Protesting  mildly  against  "  sole "  and 
"  immediate,"  I  accept  the  impeachment.  It  calls  for  no  defence. 

THE  DEVELOPMENT  OF  RECENT  THEORIES. 

Given  the  idea  of  an  underground  water-circulation  as  the 
chief  factor  in  the  deposition  of  ore,  the  next  step  in  the  in- 
quiry as  to  the  genesis  of  such  deposits  is  the  endeavor  to  de- 
termine which  particular  part  of  the  general  water-circulation 
is  responsible  for  the  results.  Around  this  question  have  cen- 
tered the  controversies  of  a  generation,  and  to  these  controver- 
sies we  owe  the  gradual  clarification  of  our  ideas  upon  the  pro- 
cesses of  ore-formation.  It  is  unnecessary  to  sketch  here  their 
progress  from  Werner  to  Le  Conte,  who  combated  in  1883  the 
extreme  views  of  the  lateral-secretionists,  and  in  1893  opposed 
the  narrow  interpretation  of  the  ascensionist-theory.  The  gen- 
erally accepted  opinions  of  to-day  are  a  well-deserved  tribute  to 
his  philosophic  discrimination. 

Thanks  to  Prof.  Van  Hise  and  Mr.  Slichter,  whose  work  he 
utilizes,  we  have  now  arrived  at  a  comprehensive  conception 

*  Trans.,  vol.  xxiv.,  966. 


THE    FORMATION    OF    BONANZAS    IN   GOLD-VEINS.  735 

of  the  underground  circulation,  which  emphasizes  the  conclu- 
sion that  sulphide-ores  are  generally  deposited  by  ascending 
waters.  In  estimating  the  importance  of  this  conclusion,  it  is 
to  be  remembered  that,  apart  from  placers  and  iron-mines,  the 
largest  portion,  by  far,  of  the  ores  exploited  by  the  miner  are 
sulphides.  Morever,  it  has  been  shown  that  the  other,  equally 
essential,  parts  of  the  circulation^  namely,  its  lateral  and  de- 
scending portions,  particularly  the  latter,  also  play  their  part, 
to  which  many  "  secondary  enrichments  "  are  due. 

This  approach  toward  an  understanding  of  the  processes  ot 
secondary  enrichment  in  ore-deposits  is  an  extremely  important 
advance  in  the  application  of  geology  to  the  exploitation  of 
mines.  For  such  enrichments  pre-eminently  constitute  the  ore- 
masses  valuable  to  man.  Chemistry  and  physics  may  unite  in 
determining  the  conditions  favorable  to  the  precipitation  of  gold; 
geology  may  unravel  the  intricacies  of  rock-structure,  but  it 
does  not  come  within  the  province  of  these  sciences  to  decide 
whether  a  gold-vein  will  prove  rich  enough  for  profitable  min- 
ing. Nature  knows  no  ratio  of  sixteen  to  one,  or  any  other 
standard  of  monetary  value.  Therefore,  the  determination  of 
the  particular  conditions  favorable  to  the  mere  occurrence  of 
gold-ores  remains  but  a  barren  discovery  until  it  includes  some 
suggestion  as  to  the  search  for  the  richest  portions.  To  the 
geologist,  material  carrying  2  dwts.  of  gold  per  ton  is  as  truly  an 
auriferous  deposit  as  if  it  contained  12  dwts.  per  ton ;  but,  under 
existing  economic  conditions,  the  miner  may  regard  the  former 
as  only  fit  for  macadam,  and  the  latter  as  potential  of  fortune. 

When  the  science  of  ore-deposits,  therefore,  has  predicted 
with  certainty  the  places  where  gold  can  be  found,  it  has  ful- 
filled a  conclusive  test  of  a  true  theory.  But  this  means  to  the 
miner  no  more  than  the  restriction  of  his  search  for  profitable 
gold-deposits  to  those  places  where  there  is  any  gold  at  all — a 
restriction  which,  after  all,  amounts  to  little,  for  the  progress 
of  scientific  inquiry  and  practical  exploration  has  rather  en- 
larged than  diminished  the  field  of  the  distribution  of  this 
metal.  A  greater  service  will  be  the  determination  of  the  con- 
ditions which  control  the  formation  and  distribution  of  those 
particular  portions  of  the  multitudinous  deposits  of  gold  which 
constitute  the  secondary  enrichments  of  the  geologist  and  the 
bonanzas  of  the  miner. 


736  THE   FORMATION    OF    BONANZAS    IN  GOLD-VEINS. 

Such  a  desired  consummation  seems  now  to  be  nearer  of 
attainment.  The  practical  result  of  the  papers  of  Messrs. 
Van  Hise,  Emmons  and  "Weed  will  he  to  direct  attention  to  the 
one  line  of  inquiry  most  useful  to  the  miner.  Unquestionably 
the  theories  of  secondary  enrichment  have  been  largely  sug- 
gested by  the  experience  of  the  men  whom  the  geologists  have 
met  at  the  mines ;  and  the  invaluable  assistance  thus  given  to 
mining  engineers  is  a  pleasant  outcome  of  such  an  exchange 
of  views. 

THE  ENRICHMENT  OF  GOLD- VEINS  NEAR  THE  SURFACE. 

A  quartz  lode  carrying  gold  in  association  with  pyrite  is  here 
taken  as  the  type  of  deposit  under  discussion.  In  lodes  of  this 
kind,  it  is  a  common  experience  to  find  bodies  of  rich  oxidized 
ores  extending  to  a  variable  depth  from  the  surface.  In  this 
general  phenomenon  of  enrichment  two  processes  must  be 
separately  recognized,  namely,  relative  enrichment  by  a  method 
of  natural  concentration  and  positive  enrichment  by  the  de- 
position of  additional  gold  through  secondary  reactions. 

Enrichment  by  Concentration. 

The  iron  sulphide  accompanying  the  gold  is  removed  by 
weathering.  Weathering  is  a  process  of  chemical  decomposi- 
tion and  mechanical  disintegration  in  which  oxidation  is  aided 
by  the  shattering  of  the  rock  due  to  the  alternate  expansion 
and  contraction  of  the  water  present  in  its  pores,  seams  and 
cavities.  The  depth  to  which  these  effects  extend  will  depend 
upon  the  facilities  afforded  for  the  penetration  of  surface- 
waters  carrying  free  oxygen;  and  it  will  be  regulated  by  the 
local  groundwater-level.  The  results  observed  usually  cease  at 
the  groundwater-level  because  at  that  horizon  the  descending 
surface-waters  become  mingled  with  the  larger  body  of  neu- 
tralized water,  and  so  lose  their  free  oxygen.  When,  however, 
they  can  find  channels  permitting  a  relatively  rapid  passage, 
they  may  not  become  at  once  diffused,  and  may  thus  continue 
their  oxidizing  action  even  below  that  level.  But  the  actual 
lowering  of  the  groundwater-level,  by  a  change  of  surface  alti- 
tude or  hydrostatic  conditions,  affords  the  chief  factor  in  en- 
larging the  scope  of  such  oxidizing  action  on  the  part  of  the 
surface-waters. 


THE    FORMATION    OF    BONANZAS    IN   GOLD-VEINS.  737 

The  chemistry  of  the  process  is  pretty  well  understood,  and 
need  not  be  discussed  here. 

In  the  case  of  enrichment  by  concentration,  the  evidence 
indicates  that  the  leaching  and  removal  of  the  pyrite  has  been 
affected  without  shifting  the  gold,  which  remains  behind  in  its 
native  state.  I  have  specimens  from  Idaho  and  West  Australia 
exhibiting  crumbly  native  sulphur,  within  the  cubic  cavities 
vacated  by  the  pyrite,  and  in  those  from  West  Australia  there 
is  also  gold  in  fine  crystals  which  are  readily  shaken  loose. 
The  removal  of  pyrite  ;  the  occurrence  of  fine  particles  of  gold 
in  the  vacant  casts  produced  by  this  removal,  and  the  forma- 
tion of  a  sintery  honeycombed  mass  of  iron-stained  quartz  are 
familiar  aspects  of  the  process  of  natural  concentration. 

Weathering,  then,  by  removing  the  baser  and  more  soluble 
constituents  of  the  vein,  decreases  the  weight  without  dimin- 
ishing the  volume  of  the  ore,  which  thus  becomes  so  much  the 
richer  per  ton.  Iron-stained  gossan,  rich  in  gold,  is  a  familiar 
occurrence  in  mining,  and  the  frequent  discovery  of  such 
material  has  had  a  far-reaching  effect  in  determining  the  char- 
acter of  the  industry.  Apart  from  the  richness  of  suck  oxi- 
dized ore,  its  metallurgical  docility  greatly  enhances  its  value. 
In  comparison  with  the  unaltered  and  relatively  refractory 
pyritic  ores,  the  oxidized  material  is  not  only  easier  to  crush, 
but  also  easier  to  treat  by  amalgamation,  chlorination,  etc. 
Hence  the  contrast  which  is  occasionally  offered  between  the 
early  successes  of  the  discoverers  of  a  gold-vein  and  the  sub- 
sequent troubles  of  the  mining  company  which  buys  their 
property.  The  gossan  of  the  gold-vein  has  been  the  source  of 
a  large  part  of  the  world's  store  of  the  precious  metal ;  and  to 
it  we  owe  the  successful  beginnings  of  many  districts,  which, 
if  they  had  been  compelled  to  commence  operations  upon  re- 
fractory pyritic  ore,  would  have  waited  long  for  their  active 
development. 

Secondary  Enrichments  Due  to  Descending  Surface-  Waters. 

The  diagnosis  of  the  general  process  by  which  these  are 
formed  by  descending  waters  has  been  stated  in  clear  terms 
in  the  contributions  of  Messrs.  Van  Hise,  Emmons  and  Weed. 

The  occurrence  of  restricted  bodies  of  extraordinarily  rich 
gold-bearing  quartz  has  been  a  startling  feature  of  gold-mining 


738  THE    FORMATION    OF    BONANZAS    IN   GOLD-VEINS. 

in  all  countries.  From  them  fortunes  have  been  made  with 
picturesque  suddenness ;  and  by  means  of  them  the  inexperi- 
enced have  been  led  into  sanguine  expectations,  the  failure  of 
which  has  brought  disasters  not  less  romantic,  though  much 
less  welcome  to  their  victims.  Such  instances  have  furnished 
matter  for  proverbs  concerning  the  uncertainty  of  mining ;  but 
they  are  soon  forgotten.  Nevertheless,  the  uncertain  occur- 
rences of  rich  ore  on  which  they  are  based  present  an  important 
feature  of  the  ore-deposits  in  all  gold-mining  districts,  though 
they  are  more  particularly  characteristic  of  desert  regions, 
such  as  the  area  of  the  Great  Basin,  stretching  between  the 
Rocky  Mountains  and  the  Sierra  Nevada,  and  also  those  arid 
parts  of  Australia  which  have  yielded  so  much  of  the  wealth 
of  the  colonies. 

The  outcrop  of  a  gold-vein  is  not  always  the  richest  portion. 
The  sintery  gossan  formed  at  the  immediate  surface  may  be 
poor  in  gold,  and  yet  may  be  succeeded  near,  or  even  below, 
the  water-level,  by  extremely  rich  masses  of  half-decomposed 
pyritic  ore.  In  such  cases  it  wrould  appear  that  the  gold  had 
been  leached  out  of  the  oxidized  portion  of  the  lode,  and  had 
migrated  in  the  wake  of  the  iron  until  precipitated,  so  as  to 
form  the  secondary  enrichment  now  under  discussion. 

In  considering  the  formation  of  these  bonanzas,  one  of  the 
first  problems  presented  is  the  question  of  the  mode  of  occur- 
rence of  the  gold  in  the  pyritic  quartz  of  the  lode.  The  evidence 
as  yet  available  indicates  that  the  gold  does  not  exist  in  chemi- 
cal combination  with  the  iron  sulphide  of  the  pyrite,  but  usually 
occurs  in  minute  filaments  or  crystal  aggregates  distributed 
through  the  substance,  and  especially  along  the  structural 
planes,  of  the  pyrite.  In  my  collection  I  have  a  handful  of 
fragments  of  pyrite  obtained  from  the  Orphan  Boy  mine,  in 
Boulder  county,  Colo.  This  mine  was  the  beginning  and  end 
of  a  mining  excitement  which  happened,  in  the  spring  of  1892, 
in  connection  with  a  locality  named  Copper  Rock.  Under  a 
magnify  ing-glass  the  specimens  exhibit  little  crystals  of  gold, 
which,  by  the  rounding  of  their  edges,  appear  in  places  as 
globules  distributed  over  the  facets  and  in  the  crevices  of  the 
pyrite. 

The  behavior  of  such  gold-ore  under  metallurgical  treatment 
also  suggests  strongly  that  its  usual  mode  of  occurrence  is 


THE    FORMATION    OF    BONANZAS    IN   GOLD-VEINS.  739 

analogous  to  the  above  example.  When  gold-bearing  pyrite  is 
treated  by  cyanidation,  the  gold  may  be  leached  out  without 
deformation  of  the  pyrite  or  any  other  change  in  its  appearance 
except  the  acquisition  b}^  its  facets  of  a  pitted  surface  suggest- 
ing cavities  left  by  the  removal  of  a  soluble  constituent.  More- 
over, there  are  many  mining  districts  yielding  gold  from  pyritic 
veins  in  which  the  native  metal  is  rarely  seen.  The  ores  of 
Gilpin  county,  in  Colorado,  for  exam  pie  j  contain  an  average  of 
from  10  to  15  per  cent,  of  iron  and  copper  pyrites ;  and  I  know 
from  frequent  trial  that  when  crushed  and  washed  in  a  pan, 
such  material,  even  though  very  rich,  will  not  yield  a  "  color," 
that  is,  a  speck  of  visible  metallic  gold.  Nevertheless,  in  the 
stamp-mill  these  ores  yield  their  gold  to  amalgamation,  indicat- 
ing by  their  behavior  in  this  respect  that  the  gold  is  in  a  condi- 
tion of  such  freedom  as  to  permit  its  separation  by  a  crude 
mechanical  process,  and  its  subsequent  ready  combination  with 
mercury  so  as  to  form  an  amalgam. 

The  gold  which  occurs  thus  in  the  pyrite  of  the  quartz-vein 
is  soluble  in  many  natural  reagents,  some  of  which  are  formed 
in  the  very  process  of  weathering  which  leaches  the  pyrite, 
while  others  are  known  to  be  present  in  the  surface-waters 
which  circulate  through  the  lode-fractures  under  observation 
at  the  present  day.  By  whatever  means  it  is  dissolved,  the 
gold  is  then  supposed  to  be  carried  by  the  surface-waters  in 
their  descent  toward  the  ground  water-level,  where  it  is  pre- 
cipitated under  conditions  to  be  discussed  in  due  course. 

Solvents. 

In  the  process  of  weathering,  the  pyrite  yields  many  subor- 
dinate compounds,  such  as  sulphuretted  hydrogen,  sulphurous 
and  sulphuric  acid,  and  proto-  and  sesqui-sulphates  of  iron.  Of 
the  latter,  the  sesqui-sulphate,  Fe2(S04)3,  is  a  solvent  for  gold, 
and  has  been  cited  by  Wurtz  and  Le  Conte  in  early  discussions 
concerning  the  origin  of  masses  of  native  gold  in  oxidized 
,  ores.  Dr.  Richard  Pearce,  in  later  years,  has  frequently  drawn 
attention  to  the  probability  that  this  sesqui-sulphate  is  a  factor 
in  the  process  of  gold-deposition.* 

The  gold-deposits  in  the   cavernous  quartzite  of  Battle  Mt., 

*  Presidential  Address,  Proc.  Colo.  Sci.  Soc.,  vol.  in.,  part  ii.  (1889),  p.  244. 

47 


740  THE    FORMATION    OF    BONANZAS    IN   GOLD-VEINS. 

Colo.,*  have  characteristics  which  appear  to  confirm  this  view. 
In  these  ores  large  pieces  of  native  gold,  of  a  nuggety  appear- 
ance, but  really  crystalline  in  structure,  have  been  found  asso- 
ciated with  horn-silver  and  the  sesqui-sulphate  of  iron.  The 
latter  occurs  in  lumps,  mixed  with  clay ;  and  although  these 
are  very  rich  in  gold,  the  gold  occurs  in  a  form  not  to  be  de- 
tected by  careful  panning.  Analyses  of  several  large  lots  of 
ore  showed  the  presence  of  12  per  cent,  of  the  hydrated  sesqui- 
sulphate  of  iron.f 

But  other  solvents,  capable  of  doing  this  work,  also  occur  in 
nature,  and,  although  the  amount  of  any  one  of  them  to  be  de- 
tected in  existing  surface-waters  may  be  minute,  we  have  to  re- 
member that  the  processes  of  nature  are  permitted  so  much 
more  time  than  those  of  the  laboratory  that  the  dilution  of  the 
solution  is  compensated  by  the  quantity  of  it. 

Most  writers  refer  to  chlorine  as  a  possible  reagent.  Such  a 
reference  is  suggested  not  only  because  it  is  a  prominent  re- 
agent in  the  metallurgical  practice  of  to-day,  but  also  by  the 
fact  that  it  has  a  wide  distribution  throughout  nature  in  the 
form  of  common  salt.  This  is  most  apparent  in  arid  regions 
where  evaporation  causes  concentrated  solutions  to  be  formed. 
Thus,  in  the  deserts  of  West  Australia  the  w^ater  encountered 
in  the  mines  is  always  brackish,  and  frequently  contains  more 
salt  than  the  sea.J  The  water  of  the  Great  Boulder  Proprie- 
tary mine,  at  Kalgoorlie,  in  1897,  contained  6402  grains  of 
common  salt  per  gallon.  §  A  considerable  amount  of  magne- 
sium chloride  was  also  present.  In  some  of  the  water  used  in 
the  stamp-mills,  and  obtained  from  temporary  "  lakes," ||  the 
salts  were  present  up  to  the  point  of  saturation  and  the  liquid 
carried  further  salts  in  suspension,  so  that  the  amount  reached 
as  high  as  30  per  cent.,  rendering  the  term  "  brine  "  more  suit- 
able than  "  water."  This  liquid  contained  17  per  cent,  of  salts 
in  solution  even  when  most  diluted  by  recent  rains,  and  it 
therefore  afforded  a  parallel  to  the"  Dead  Sea,  the  waters  of 

*  F.  Guiterman,  "Gold  Deposits  in  the  Quartzite  Formation  of  Battle  Moun- 
tain, Colorado,"  Proc.  Colo.  Sci.  Soc.,  vol.  iii.,  part  iii.  (1890),  pp.  264-268. 

i  Ibid.,  p.  266. 

J  Sea-water  contains  3£  per  cent,  of  salts,  three-quarters  of  which  is  common 
salt,  the  chloride  of  sodium.  %  This  is  equivalent  to  9  per  cent. 

||  "Sinks"  or  salt-marshes.  They  form  an  important  feature  of  the  physiog- 
raphy of  West  Australia. 


THE    FORMATION    OF    BONANZAS    IN   GOLD-VEINS.  741 

which  contain  from  20  to  26  per  cent,  of  salts,  of  which  10  per 
cent,  is  common  salt.  These  excessive  percentages  are  not  due 
to  the  presence  of  deposits  of  salt  in  the  rocks  of  the  district, 
but  simply  to  the  concentration  brought  about  by  the  excessive 
evaporation*  which  takes  place  in  a  hot,  arid  climate. 

Mine-waters  frequently  contain  a  noteworthy  quantity  of 
chlorine,  as  chloride  of  sodium.  At  the  Mammoth  mine,  in 
Final  county,  Arizona,  the  water  carries  five  grains  of  salt  per 
gallon,  while  the  well-water,  used  in  the  stamp-mill,  situated  in 
the  valley  below  the  mine,  contains  twice  as  much.f  This 
would  be  equivalent  to  six  grains  of  free  chlorine  per  gallon. 
The  larger  amount  contained  in  the  water  from  the  well,  as 
compared  with  that  in  the  drainage  of  the  mine,  suggests  the 
results  of  surface-leaching.  Even  in  mountainous  districts, 
such  as  Cripple  Creek,  Colo.,  the  mine-waters  carry  chloride 
of  sodium  to  a  noteworthy  extent.  The  water  of  the  Inde- 
pendence mine  contains  three  grains  per  gallon. 

Another  suggestive  feature  is  offered  by  the  abundance  of 
horn-silver  or  cerargyrite,  the  chloride  of  silver,  throughout  the 
dry  tracts  of  Arizona,  New  Mexico  and  Nevada.  J  Prof.  Pen- 
rose  emphasizes  this  interesting  fact,  and  connects  it  with  the 
bodies  of  salt  water  which  still  survive  in  places  as  "  sinks  " 
and"  lakes. "§  Furthermore,  the  oxy-chloride  of  copper,  ata- 
camite  (which  derives  its  name  from  the  Atacama  desert,  be- 
tween Chili  and  Peru),  is  frequent  in  these  regions.  Another 
and  more  uncommon  mineral  may  also  be  mentioned  in  this 
connection.  In  the  Mammoth  mine,  already  cited,  and  in  the 
well-known  Vulture  mine,  both  in  Arizona,  the  precious  metals 
are  associated  with  vanadinite,  which  contains  chlorine  as  a 
chloro-vanadate  of  lead,  3Pb3(V04),;  PbClr  ||  Thus  the  chlorides 
of  copper,  lead  and  silver  are  found  in  the  oxidized  ores  of 
these  regions,  while  the  corresponding  combination  of  gold  is 

*  The  rate  of  evaporation,  in  the  region  mentioned,  has  been  estimated  to  be 
as  much  as  7  ft.  per  annum. 

t  As  I  am  informed  by  Mr.  T.  G.  Davey. 

J  The  general  occurrence  of  horn-silver  in  the  outcrops  of  lodes  throughout 
the  southern  parts  of  Arizona  and  New  Mexico  has  originated  the  term  "chlorid- 
ing"  which  the  miners  employ  as  a  synonym  for  "  prospecting,"  which,  by  the 
way,  the  Australian  calls  "fossicking." 

\  R.  A.  %F.  Penrose,  Jr.,  "The  Superficial  Alteration  of  Ore-Deposits,"  The 
Journal  of  Geology,  vol.  ii.,  p.  288,  1894.  ||  Dana. 


742  THE    FORMATION    OF    BONANZAS    IN    GOLD-VEINS. 

absent.  The  explanation  is  obvious.  The  chloride  of  gold  is 
an  unstable  and  readily  soluble  compound,  while  the  minerals 
formed  by  the  corresponding  combination  with  the  baser 
metals  are  comparatively  insoluble  in  water,  especially  the 
chloride  of  silver,  for  the  abundance  of  which  there  is  therefore 
a  good  reason.  It  remains  but  to  add  that,  in  several  Arizona 
mines  which  I  have  sampled,  the  ores  above  the  water-level 
carried  a  notable  proportion  of  silver  with  very  little  gold, 
while  in  depth  the  silver  contents  have  diminished  and  the 
gold  has  increased,  especially  in  the  vicinity  of  the  water- 
level.* 

Of  the  many  reagents  which  would  liberate  the  chlorine 
from  salt,  it  is  only  necessary  to  mention  ferric  sulphate  and 
sulphuric  acid,  both  derived  from  the  ordinary  oxidation  of 
pyrite.  The  hydrochloric  acid  thus  formed  would  yield  free 
chlorine  in  the  presence  of  manganese  oxides, f  which  are  very 
prevalent  in  the  upper  portion  of  gold-lodes,  in  the  form  of  the 
black  earthy  mineral,  psilomelane. 

There  are  other  possible  solvents  which  need  not  be  dis- 
cussed here. 

Precipitants. 

Whatever  the  solvents  which  leach  out  the  gold  from  the 
superficial  portions  of  the  vein,  there  is  assuredly  no  lack  of 
precipitants.  It  is  probable  that  the  gold  does  not  migrate  far 
before  encountering  conditions  which  compel  deposition.  Even 
when  it  is  eventually  carried  to  a  considerable  distance  it  is 
most  likely  that  such  removal  is  effected  by  alternating  stages 
of  precipitation  and  solution. 

Organic  matter  is  a  probable  precipitant  for  the  gold  in 
such  surface-waters.  It  exists  deeper  than  hasty  observation 
would  suggest.  At  the  Great  Boulder  Main  Reef  mine,  at 
Kalgoorlie,  I  saw  the  roots  of  trees  which,  in  their  energetic 
search  for  moisture,  had  attained  a  depth  of  85  ft,  below  the 
surface ;  and  at  the  Sugar  Loaf  mine,  near  Kunanalling  (also  in 
West  Australia),  I  saw  a  similar  occurrence  at  a  depth  of  74  ft,  J 

*  I  may  instance  two  well-known  mines,  the  Mammoth  and  the  Commonwealth. 

f  See  the  experiments  made  by  Dr.  Don,  to  test  this  matter,  Trans.,  xxvii., 
p.  599. 

J  Since  writing  the  above  I  have  read  Professor  Vogt's  very  valuable  contribu- 
tion, and  I  note  that  he  mentions  having  seen,  among  the  mineral  exhibits  at 


THE    FORMATION    OF    BONANZAS    IN    GOLD-VEINS.  743 

Another  agency  which,  under  certain  chemical  conditions, 
is  a  probable  factor  in  reducing  the  gold  from  surface-waters, 
is  pyrite  itself.  Thus,  the  gold  dissolved  from  the  decomposed 
pyrite  at  the  surface  may  be  precipitated  upon  the  unoxidized 
pyrite  deeper  down.  Among  the  exhibits  belonging  to  the 
Colorado  Scientific  Society  is  a  bottle  containing  cubes  of 
pyrite,  on  the  faces  of  which  crystals  of  gold  are  to  be  seen. 
They  are  the  result  of  one  of  Dr.  Pearce's  experiments.  The  gold 
of  a  Cripple  Creek  ore  was  dissolved  by  using  common  salt,  sul- 
phuric acid  and  psilomelane  as  reagents,  the  chlorine  being 
thus  obtained  in  a  manner  analogous  to  conditions  which  prob- 
ably occur  in  nature.  This  solution  was. placed  in  a  small 
bottle,  and  to  it  were  added  a  few  large  pure  crystals  of  pyrite 
from  the  St.  Louis  mine,  at  Leadville.  After  several  months 
the  gold  became  precipitated  in  the  manner  described.  In 
this  connection  the  story  of  Daintree's  experiment,  which  I 
have  quoted  before,*  is  worth  repeating.  In  1871,  Daintree 
commenced  a  series  of  experiments  at  Dr.  Percy's  laboratory 
at  the  Royal  School  of  Mines,  London.  In  a  number  of  small 
bottles  he  placed  a  solution  of  chloride  of  gold,  and  to  each  he 
added  a  crystal  of  one  of  the  common  metallic  sulphides,  such 
as  pyrite,  blende,  galena,  etc.  At  the  time  when  Daintree 
died,  a  few  years  later,  no  results  could  be  discerned ;  but  one 
of  the  bottles,  containing  the  gold  solution  and  a  crystal  of 
common  pyrite,  was  removed  to  Dr.  Percy's  private  laboratory, 
in  Gloucester  Crescent,  and  there,  in  1886,  the  experiment  was 
completed  by  the  discovery  of  a  cluster  of  minute  crystals  of 
gold  upon  the  smooth  surface  of  the  pyrite.  The  experiment 
had  occupied  fifteen  years ;  and  on  account  of  its  very  length 
it  may  be  said  to  have  more  nearly  approached  the  actual  con- 
ditions occurring  in  nature. 

In  a  case  like  that  of  the  "  Indicator,"  at  Ballarat,  which  I 
have  lately  described  again, f  it  maybe  questioned  whether  it  is 
the  pyrite  in  the  thin  seam  of  graphitic  slate  or  the  carbonaceous 
matter  of  the  latter  which  causes  the  precipitation  of  the  gold. 


Paris,  specimsns  of  such  roots,  from  the  Great  Boulder  Main  Keef  mine,  on 
which  gold  had  actually  been  precipitated.  "  Problems  in  the  Geology  of  Ore- 
Deposits,"  this  volume,  p.  678. 

*  Trans.,  xxii.,  313. 

f  "The  Indicator  Vein,  Ballarat,  Australia,"  Trans.,  xxx.,  1004. 


744  HE    FORMATION    OF    BONANZAS    IN   GOLD-VEINS. 

Even  if  the  pyrite  was  the  decisive  factor,  it  must  be  remem- 
bered that  it,  in  turn,  probably  owed  its  previous  deposition  to 
the  action  of  the  carbonaceous  precipitant  in.  the  Indicator 
seam.  This  would  apply  also  to  the  beds  of  black  slate  which 
have  had  so  marked  an  influence  on  the  occurrence  of  gold  in 
the  Gympie  district,*  Queensland,  but  it  would  not,  I  think, 
be  applicable  to  the  Eico  deposits,f  where  pyrite  is  not  an 
especial  constituent  of  the  black  shales,  as  compared  with  the 
sandstone  beds  of  the  same  stratified  series. 

Solution  and  Precipitation. 

It  is  to  be  noted  that  in  the  two  examples  of  ore-forming  pro- 
cesses which  have  been  considered,  the  gold  in  the  superficial 
part  of  the  vein  is  supposed,  in  one  case,  to  remain  in  the  gos- 
san after  the  pyrite  has  been  removed,  while  in  the  other  in- 
stance the  gold  also  is  dissolved  and  carried  elsewhere.  This 
may  appear  contradictory.  It  is  a  good  illustration  of  the  per- 
plexities arising  from  the  application  of  chemical  hypotheses  to 
the  theory  of  ore-deposition. 

Nature  knows  no  interval  of  inaction  ;  solution  is  going  on  at 
one  time,  precipitation  at  another.  The  gold  is  constantly  the 
object  of  one  or  the  other  activity.  After  the  pyrite  is  removed, 
or  while  it  is  still  undergoing  leaching,  the  gold  is  being  dis- 
solved, but  more  slowly  than  the  baser  metals.  That  which 
remains  to  enrich  the  gossan  may  well  be  supposed  to  be,  the 
survival  from  a  larger  quantity  of  gold  which  has  been  under- 
going slow  solution.  The  gold  which  was  deposited  deeper 
down,  from  the  surface-waters,  may,  as  erosion  takes  away  the 
upper  part  of  the  vein,  eventually  find  itself  close  to  the  sur- 
face and  undergo  re-solution.  It  is  a  question  whether  the 
mining  of  to-day  breaks  in  upon  the  gold-deposits  at  one  stage 
or  another  of  a  continuous  process.  The  miner  finds  the  bal- 
ance of  gold  left  on  deposit  from  a  current  account  in  Nature's 
bank.  Solution  and  precipitation  are  everywhere  in  action  ;  it  is 
the  excess  of  one  or  the  other  which  determines  the  formation 
of  ores. 


*  J.  E.  Don,  "  The  Genesis  of  Certain  Auriferous  Lodes,"  Trans.,  xxvii.,  577- 
580. 

f  "The  Enterprise  Mine,  Eico,  Colorado,"  Trans.,  xxvi.,  906. 


THE  FORMATION  OF  BONANZAS  IN  GOLD-VEINS.  745 

THE  DISTRIBUTION  OF  ORE-BONANZAS. 

The  shifting  of  the  zone  of  oxidation  is  a  principal  factor  in 
determining  the  distribution  of  rich  ores.  By  the  erosion  of 
the  superficial  portions  of  the  vein,  in  common  with  the  en- 
closing rock,  the  further  downward  penetration  of  the  oxidiz- 
ing agencies  is  facilitated.  The  depression  of  the  ground- 
water-level  lowers  the  zone  at  which  precipitation  of  gold,  from 
descending  surface-waters,  takes  place,  while,  on  the  other  hand, 
when  a  change  in  the  hydrostatic  level  causes  the  groundw^ater 
to  rise,  the  zone  of  deposition  moves  up.  In  both  cases  the 
tendency  is  to  give  vertical  extension  to  the  rich  mass  of  sec- 
ondary gold-ore,  and  thus  to  produce  the  occurrence  which 
miners  term  a  "  shoot." 

Erosion  is  followed  by  another  result,  in  itself  of  great  im- 
portance to  gold-mining.  The  steady  removal  of  the  super- 
ficial part  of  the  vein  causes  the  lower  portion,  which  has  been 
enriched  at  or  below  the  ground  water-level,  to  undergo  a  rela- 
tive elevation  by  being  brought  nearer  to  the  surface.  In  this 
way  the  bonanza-zone,  in  process  of  time,  may  become  the  out- 
crop. This  appears  to  me  to  explain  the  occurrence  of  the  extra- 
ordinarily rich  bunches  of  specimen-quartz,  such  as  made  West 
Australia  famous  in  1894  and  1895,  and  started  the  mining 
stampedes  of  other  days  elsewhere.  In  many  instances  for- 
tunes have  been  gathered  almost  at  the  grass-roots  from  veins 
which,  on  systematic  development,  have  proved  unprofitable. 
The 'gold-quartz  veins  of  West  Australia  traverse  rocks  of 
great  geological  antiquity  which  have  not,  during  late  geolog- 
ical periods,  undergone  any  notable  disturbance.  We  do  not 
know  at  what  period  the  veins  were  formed ;  but,  even  though 
their  formation  dates  no  further  back  than  the  beginning  of 
the  Tertiary,  they  have  since  been  continuously  exposed  to  the 
same  quiet  forces  of  erosion  which  have  leveled  the  region 
until  it  appears  as  an  arid  table-land  strewn  with  the  wreckage 
of  geological  time. 

Whatever  the  alternations  of  slow  depression  and  elevation 
which  have  affected  this  region,  as  part  of  a  continental  area, 
it  is  certain  that  erosion  has  been  long  at  work  with  patient 
constancy.  Throughout  this  period  chemical  agencies  have 
been  active  in  the  zone  of  weathering,  near  the  surface,  remov- 
ing the  gold  to  the  zone  of  precipitation,  near  the  groundwater. 


746  THE    FORMATION    OF    BONANZAS    IN   GOLD-VEINS. 

Whatever  the  slight  changes  which  have  marked  the  level  of 
the  groundwater  from  time  to  time,  erosion  has  continued  un- 
interruptedly, and  therefore  it  has  steadily  gained,  with  the 
result  that  the  enriched  portion  of  the  vein  has  been  brought 
nearer  and  nearer  to  the  actual  surface,  until  it  finally  appears 
as  the  outcrop  which  rewards  the  search  of  the  prospector. 

The  Localization  of  Ore-Shoots. 

To  the  miner  the  localization  of  these  richer  portions  of  the 
vein  is  of  more  immediate  practical  interest  than  the  theory  of 
their  origin.  A  gold-vein  is  not  a  homogeneous  mass  of  aurif- 
erous quartz,  of  tabular  form,  penetrating  the  rocks  like  a 
sheet  of  paper,  but  rather  as  an  irregular  occurrence  of  ore,  the 
composition  and  shape  of  which  are  very  variable,  because  they 
are  the  result  of  chemical  agencies  and  structural  conditions  of 
great  complexity.  While  the  traces  of  the  agencies  which  pre- 
cipitated the  ore  are  obscure,  because  they  have  been  largely 
obliterated  by  subsequent  chemical  action,  the  relation  between 
the  vein  and  its  encasing  rock  can  often  be  traced  by  observa- 
tion. In  this  direction  the  miner  obtains  great  aid  from  the 
geologist.  The  transactions  of  this  Institute  and  the  publica- 
tions of  the  U.  S.  Geological  Survey  contain  numerous  clear 
expositions  of  such  structural  relations.  The  monographs  on 
the  Leadville  and  Eureka  mining  districts  may  be  especially 
instanced  as  affording  striking  examples  of  the  direct  applica- 
tion of  geology  to  underground  work. 

Australia. — One  of  the  best  examples  of  the  localization  of 
rich  ore  came  under  my  notice  in  1890  in  the  Bright  mining 
district.  Bright  is  geographically  in  the  Australian  Alps,  and 
geologically  in  the  Upper  Silurian  slates  and  sandstones. 
Though  these  rocks  have  undergone  metamorphism,  and  ex- 
hibit a  well-developed  cleavage,  yet  their  bedding  has  not  been 
obliterated.  The  veins  cross  the  bedding-planes  of  the  enclos- 
ing country  both  in  strike  and  dip.  When  investigating  the 
distribution  of  the  ore  in  the  mines  of  this  district,  I  found  that 
the  ore-shoots  had  a  pitch  corresponding  with  the  line  of  inter- 
section between  vein  and  country.  This  was  well  illustrated  at 
the  Shouldn't  Wonder  mine,  7  miles  from  the  town  of  Bright. 
The  lode  was  a  simple  quartz  vein  from  15  to  24  in.  Avide, 
carrying  a  small  percentage  of  pyrite.  It  had  a  strike  of  N". 


THE    FORMATION    OF    BONANZAS    IN    GOLD-VEINS.  747 

28°  W.  and  a  dip  to  the  KE.  of  about  75°,  while  the  country 
dipped  SW.  79°  and  had  a  strike  of  N.  55°  W.  The  plane  of 
the  vein  cut  across  the  beds  of  the  country  and  the  intersec- 
tions thus  produced  were  to  be  seen  along  the  foot-wall  of  the 
lode  as  lines,  pitching  42°  to  46°  southward.  While  the  foot- 
wall  was  more  regular  than  the  hanging,  and  therefore  ex- 
hibited this  feature  best,,  yet  the  hanging  also  carried  lines  cor- 
responding with  those  observed  on  the  opposite  wTall. 

The  boundaries  of  the  ore-shoots  in  the  mine  followed  these 
lines ;  and  the  longitudinal  section  of  the  workings,  as  seen  on 
the  mine-maps,  proved  also  that  these  lines  of  intersection  had 
an  inclination  which  coincided  writh  the  trend  of  the  ore-bodies, 
as  stoped  out  between  the  four  successive  upper,  levels  of  the 
property. 

At  the  Myrtle  mine,  in  the  same  district,  there  was  the  same 
correlation  between  the  pitch  of  the  ore-bodies  and  the  line  of 
intersection  of  the  wall  of  the  lode  with  the  bedding-planes  of 
the  enclosing  country.  The  stratification  was  distinct,  the 
rocks  consisting  of  altered,  silicified  slates  of  a  gray  to  gray- 
blue  tint.  In  the  stopes  above  the  700-ft.  level  the  pay-ore  was 
separated  from  the  normal  valueless  quartz  of  the  lode  by  a 
small  step,  due  to  the  irregular  fracture  of  the  vein  in  crossing 
two  beds  of  unequal  hardness.  It  marked  the  line  of  inter- 
section between  lode-plane  and  country  bedding,  and  also 
proved  to  be  the  boundary  of  the  pay-shoot.  In  the  different 
portions  of  the  mine  the  variation  in  the  dip  of  the  country 
produced  variations  in  the  angle  of  the  lines  of  intersection, 
and  also  in  the  pitch  of  the  ore-shoots. 

It  is  not  often  that  the  formation  traversed  by  a  vein  has 
such  a  simple  structure  as  was  presented  by  these  Silurian 
sedimentary  rocks;  but  it  is  probable  that  m  other  districts 
also  the  pitch  of  the  ore-bodies  may  have  been  determined  by 
structural  conditions  of  a  similar  kind,  which  have  been  ob- 
scured, however,  by  metamorphism. 

Colorado. — Experience  has  shown  that  the  intersection  of 
fractures  favors  the  occurrence  of  rich  ore-bodies.  An  inter- 
esting example  was  afforded  by  the  Moon-Anchor  mine,  at 
Cripple  Creek,  in  1899.  This  is  illustrated  in  Fig.  1.  The  ore 
in  the  mine  occurs  in  a  lode-channel  marked  by  a  band  of 
fractured  andesite  breccia.  At  the  400-ft.  level  a  small  dike 


748 


THE    FORMATION    OF    BONANZAS    IN    GOLD-VEINS. 


(EF)  of  granite,  2  to  6  in.  thick,  intersects  the  lode-channel  at 
a  place  where  a  counter-fracture  (CD)  also  traverses  it.  A 
triangle  is  produced  by  these  intersections,  and  the  ore  is 
proved  to  surround  a  block  of  ground  which  is  also  mineralized, 
but  not  sufficiently  so  to  be  regarded  in  its  entirety  as  pay-ore. 


FIG.  1. 


—  ' 


FORMATION   OF   ORE 
AT  INTERSECTION    OF    FRACTURES 

SCALE,  ABOUT  3o'=  1  IN. 


i  CR066  DIKE 


ANDESITE  BRECCIA 


MOON   ANCHOR   MINE,   CRIPPLE    CREEK. 


Borma»  *  Co. .  If.  Y. 


At  the  crossing  of  the  dike   and  cross-fractures   a  very  rich 
body  of  telluride-ore  was  encountered. 

This  reminds  me  of  the  Yankee  Girl  ore-body,  mentioned 
by  Emmons.*  This  body  of  ore  was  of  phenomenal  richness, 
many  ten-ton  lots  being  shipped  which  carried  7  or  8  ounces  of 
gold  and  3000  to  4000  ounces  of  silver  per  ton.  The  ore  was 
also  rendered  remarkable  by  carrying  the  rare  mineral  stro- 
meyerite,  a  sulphide  of  silver  and  copper.  Mr.  Emmons  speaks 

*•  "The  Secondary  Enrichment  of  Ore-Deposits,"  this  volume,  p.  451. 


THE    FORMATION    OF    BONANZAS    IN   GOLD-VEINS.  749 

of  the  bonanza  turning  into  low-grade  pyritic  ore  as  depth  was 
attained.  I  may  add*  that  this  change  was  not  gradual,  but 
sudden,  and  coincident  with  certain  structural  relations.  At 
the  surface,  the  vein  consisted  of  comparatively  low-grade  ore, 
which  led  to  the  finding  of  a  nearly  vertical  "  chimney,"  aver- 
aging only  25  to  30  ft.  in  diam.,  of  extraordinarily  rich  ore, 
consisting  of  the  copper  sulphides,  bornite  and  erubescite,  with 
stromeyerite  and  barite.  The  gold  in  the  ore  was  associated 
with  the  barite.  From  the  second  to  the  sixth  level,  at  about 
500  ft.  below  the  surface,  this  bonanza  proved  immensely  pro- 
ductive; then,  suddenly,  aflat  floor,  dipping  W.  and  accompanied 
by  clay,  crossed  the  deposit.  This  flat  vein  was  worked  for  90 
ft.,  from  the  south  drift  at  the  'No.  6  level,  and  contained  ore 
similar  to  that  of  the  Yankee  Girl  chimney.  The  latter  was  found 
again  deeper  down,  and  out  of  its  former  line  of  descent,  but 
it  was  much  diminished  in  richness,  and  appeared  to  merge  into 
the  general  body  of  low-grade  copper  and  iron  pyritesf  which 
characterized  the  lode  at  the  tenth  level.  This  mine  and  its 
neighbors,  the  Robinson  and  Guston,  are  idle  now.  They  are 
in  the  andesite  breccia  of  the  San  Juan  region.  The  Yankee 
Girl  chimney  was  situated,  I  believe,  at  the  crossing  of  three 
lode-fractures,  appearing  as  breaks  in  the  andesite,  which  was 
bleached  and  mineralized  where  they  traversed  it.  It  was  a 
curious  feature  of  this  mine,  and  of  the  Guston  also,  that  the 
short,  very  rich  bonanzas  of  the  upper  levels  gradually  lost 
their  definition,  that  is  to  say,  they  became  no  richer  than  the 
intervening  portions  of  the  lode.  This  was  interpreted  as  a 
"  lengthening  "  of  the  ore-shoots,  which  may  be  true,  viewed  in 
one  way;  but  I  think  that  it  should  be  more  properly  regarded 
as  an  impoverishment  of  the  lode,  marked  by  a  disappearance  of 
the  bonanzas.  The  surface-waters  of  these  mines  are  very  acid, 
as  Mr.  Emmons  remarks.  At  the  Yankee  Girl  mine  it  became 
necessary  to  encase  the  pipes  in  redwood,  brought  from  Cali- 
fornia. I  found  that  the  water  issuing  from  a  shallow  adit  (73  ft. 
below  the  collar  of  the  shaft)  readily  precipitated  copper  on 
scrap  iron.  Ore-forming  agencies  were  evidently  still  at  work. 
California. — In  California,  especially  in  that  mining  region 
which  follows  the  foothills  of  the  Sierra  Nevada  and  traverses 


*  From  notes  made  during  an  examination  of  the  mine  in  January,  1892. 
f  Assaying  20  to  60  ozs.  silver,  1  to  4  dwts.  gold,  5  to  15  per  cent,  copper. 


750  THE    FORMATION    OF    BONANZAS    IN   GOLD-VEINS. 

the  counties  of  Amador,  Calaveras  and  Tuolumne,  the  occur- 
rence of  pockets  of  rich  ore,  full  of  native  gold,  is  a  notable 
feature  of  the  superficial  parts  of  the  quartz-veins.  These 
pockets  appear  to  be  confined  to  the  zone  between  the  surface 
and  the  water-level,  and  to  be  dependent  upon  the  results  pro- 
duced by  the  small  cross-veins  which  encounter  the  main 
lodes.  In  1887  I  had  the  pleasure  of  extracting,  in  two  hours, 
a  little  over  170  ounces  of  gold,  worth  about  $3000,  from  one 
of  these  pockets.  It  was  at  the  Rathgeb  mine,  near  San  An- 
dreas, in  Calaveras  county.  The  main  lode  consisted  of  5  to  8 
ft.  of  massive  "  hungry-looking"  quartz,  the  foot-wall  of  which 
was  a  beautiful  augite-schist  and  the  hanging  a  hard  diabase. 
The  water-level  was  160  ft.  below  the  surface.  Down  to  this 
point,  the  country  was  oxidized,  the  hanging-wall  exhibiting 
only  slight  alteration,  while  the  schist  of  the  foot-wall  was  soft- 
ened and  decomposed  almost  to  a  clay.  This  was  traversed  by 
numerous  small  veins,  which  appeared  to  act  as  "  feeders," 
forming  bunches  of  rich  ore  where  they  encountered  the  main 
lode.  At  the  120-ff.  level,  south  from  the  shaft,  there  were  some 
old  workings ;  and  the  examination  of  these  led  to  the  discovery 
of  a  small  seam,  about  one-sixteenth  of  an  inch  thick,  filled 
with  red  clay  which  carried  a  good  deal  of  native  gold,  as  was 
proved  by  washing  it  in  a  pan.  An  experienced  miner  was  put 
to  work,  with  instructions  to  followT  this  small  streak.  It  varied 
in  thickness,  and  occasionally  opened  out  into  small  lenticular 
cavities,  containing  a  clay  in  which  the  gold  was  distributed 
like  the^raisins  in  a  pudding.  Each  of  these  "  pockets  "  yielded 
several  hundred  dollars'  worth  of  gold.  At  length  the  streak 
widened  to  6  or  8  inches  of  quartz,  lined  with  clay.  The 
amount  of  red  clay  commenced  to  increase ;  coarse  gold  be- 
came more  frequent ;  and  a  big  discovery  was  hourly  expected. 
It  was  finally  made.  The  vein  suddenly  became  faulted,  and 
at  the  place  of  faulting  there  was  a  soft,  spongy,  wiry  mass  of 
gold  and  clay — more  gold  than  clay.  The  first  handful  I  broke, 
while  yet  the  stope  was  thick  with  powder-smoke,  contained 
three  ounces  of  gold.  Within  the  next  two  hours  this  pocket 
gave  us  $3000,  and  during  the  following  week  it  yielded  over 
$20,000,  an  amount  which  was  obtained  at  a  total  cost  of  less 
than  $200.  When  it  had  been  worked  out,  it  was  easy  to  ob- 
serve the  conditions  which  determined  its  occurrence  at  this 


THE    FORMATION    OF    BONANZAS    IN   GOLD-VEINS. 


751 


place,  as  Fig.  2  will  explain.  The  vein,  AC,  had  been  faulted 
about  its  own  width,  namely,  10  inches,  by  a  small  cross-seam, 
DE,  and  at  this  intersection,  B,  the  pocket  lay.  The  gold  was 


FIG.  2. 


////  /,;//  'll(*«Mty  "I 
MmM/ 1 1 

f  ii  ^^ 

rfi 

^«^-     r     111      '  ''    ' 

I  Jm- 


I 


IL 


i 


M* 


7 


(/  ,  i 


SCHIST 


•:-.•/  NATIVE  GOLD 


CLAY  -eff5^        CROSS  8EAM 

OCCURRENCE   OF  A  'POCKET.' 


spongy  and  was  intermixed  with  quartz.  The  clay  which  pene- 
trated the  whole  mass  was  partly  red  and  ochreous,  and  partly 
a  gray  gelatinous  material.  In  the  quartz,  and  associated  with 
the  gold,  there  were  acicular  black  crystals  of  pitch-blende 


752  THE    FORMATION    OF    BONANZAS    IN   GOLD-VEINS. 

(uraninite),  together  with  uranium  ochre.     This  association  of 
gold  with  uranium  is  uncommon. 

New  Zealand. — Intersections  which  coincide  with  enrichments 
form  a  notable  characteristic  of  the  Hauraki  gold-field*  in  the 
north  island  of  New  Zealand.  In  this  district  the  occurrence 
of  patches  of  native  gold  is  an  important  feature  of  the  regular 
mining  operations.  When  I  was  there,  in  1891,  each  stamp- 
mill  had  its  "  specimen-stamp,"  a  single  stamp  working  in  a 
separate  mortar,  and  employed  solely  for  the  treatment  of  speci- 
men-ore. These  rich  patches  occur  at  the  places  where  the 
u  reefs  "  or  lodes  cross  bands  of  flinty  quartz.  The  latter  are 
known  among  the  miners  as  "  fllnties."  They  vary  in  thick- 
ness from  a  few  inches  to  mere  threads  of  chalcedonic  quartz. 
They  are  barren  in  themselves,  but  have  a  favorable  effect  on 
the  gold-veins.  The  latter  are  also  intersected  by  cross-veins, 
producing  an  enrichment  similar  to  that  caused  by  the  u  fllnt- 
ies." Fig.  3  is  a  sketch  of  one  of  these  intersections,  as  seen 
by  me  in  the  Moanataeri  mine.  The  lode,  AB,  consists  of 
a  series  of  small  seams  of  quartz,  conforming  to  the  struc- 
tural lines  of  the  enclosing  country,  which  is  hornblende-ande- 
site.  The  cross-vein,  CD,  is  a  band  of  soft  gray  decomposed 
rock,  which  also  carries  a' number  of  small  quartz-seams,  but 
only  near  its  crossing  with  the  main  lode,  AB.  The  line 
of  CD  is  parallel  to  a  large  fault,  to  be  seen  elsewhere  in  the 
mine-workings.  The  "  leaders,"  or  quartz-seams,  in  AB  are 
gold-bearing,  and  exhibit  marked  enrichment  at  the  intersec- 
tion with  CD. 

The  prevailing  formation  of  this  mining  district  is  an  ande- 
site,  which  is  traversed  by  soft  bands  of  decomposition,  called 
"  sandstone  "  by  the  miners.  The  latter,  when  penetrated  by 
quartz-seams,  are  favorable  to  the  finding  of  ore.  The  gold- 
occurrence  is  essentially  sporadic  and  dependent  upon  local  en- 
richments, such  as  have  been  described.  The  district  is  sur- 
rounded by  thermal  springs,  and  is  near  the  well-known  volcanic 
region  of  Tarawera,  which  was  active  in  1884.  The  mine- 
waters  are  heavily  mineralized  and  very  acid,  so  that  the  metal 
screens  used  in  the  mills  are  quickly  corroded.  Tellurides  and 
selenides  of  gold  have  been  detected  in  the  ores ;  but  the  pre- 


It  is  also  known  as  the  Thames  district. 


THE    FORMATION    OF    BONANZAS    IN   GOLD-VEINS. 


753 


cious  metal  is  usually  found  native  and  in  coarse  particles, 
which  are  frequently  coated  with  native  Arsenic.  The  district 
is  one  which,  I  think,  if  thoroughly  examined,  would  afford 
many  suggestions  regarding  ore-deposition.* 


vv;j 

<\      I-     "  .......,,...-,,,    , 

JBorma,  &  Co.,  A.  T. 

ENRICHMENT  AT  INTERSECTION  MOANATAERI  MINE,  NEW  ZEALAND. 

CONCLUDING  KEMARKS. 

It  is  to  be  hoped  that  the  recent  recognition  of  tho  agencies 
which  bring  about  the  formation  of  enrichments  by  surface- 
waters  will  not  cause  too  violent  a  swing  in  the  direction  of  a 
sweeping  advocacy  of  the  general  efficiency  of  descending 

*  The  best  description  which  has  come  under  my  notice  is  "The  Geology  of 
the  Thames  Goldfield,"  by  James  Park,  read  before  the  Auckland  Institute,  1894. 

See  also  "On  the  Kocks  of  the  Hauraki  Goldfields,"  by  F.  W.  Button,  Proc. 
Austral.  Assn.  Adv.  Sci.,  1888  ;  and  J.  E.  Don,  "The  Genesis  of  Certain  Auriferous 
Lodes,"  Trans.,  xxvil,  584-589. 


754  THE    FORMATION    OF    BONANZAS    IN    GOLD-VEINS. 

solutions  to  form  ore-bodies.  The  study  of  the  problems  of 
ore-occurrence  has  been  hindered  in  the  past  by  such  reactions 
from  one  extreme  vieAv  to  its  opposite.  Therefore,  in  conclud- 
ing this  contribution  to  the  discussion  of  the  results  produced 
by  descending  surface-waters,  I  would  emphasize  the  wider 
agency  of  ascending  solutions  in  forming  the  ore-masses  amid 
which  such  secondary  enrichments  are  occasionally  found.  It 
is  agreed  that  the  sulphide-ores  are  primarily  deposited  from 
ascending  waters ;  it  is  also  likely  that  such  a  result  is  repeated. 
A  region  once  subjected  to  fracturing,  which  has  permitted 
the  subsequent  passage  of  mineral-bearing  solutions,  is  likely, 
at  a  later  period,  to  be  subjected  to  a  repetition  of  these  activi- 
ties. The  geological  history  of  many  mining  regions  gives 
clear  evidence  of  a  repeated  disturbance  of  structure.  This  is 
indicated  by  the  existence  of  several  systems  of  fractures 
crossing  each  other,  the  later  ones  dislocating  the  earlier.  It 
is  probable  that  each  period  was  marked  by  mineralization,  the 
character  of  which  may  have  varied.  The  banded  arrange- 
ment of  the  lodes  of  certain  districts,  such  as  Freiberg,  Rico 
and  Butte,  suggests  this.  Enrichment  may  have  been  caused 
by  mere  addition ;  the  introduction  of  other  metals  may  have 
changed  the  average  composition  of  the  ore  in  the  lode  so  that 
it  is  now  extremely  valuable,  whereas  before  it  may  have  had 
no  economic  importance ;  a  silver-ingredient  may  have  been 
added  to  the  gold-contents,  or  the  addition  of  copper  may  have 
made  a  deposit  doubly  valuable  by  improving  its  metallurgical 
character.  I  hope  the  present  discussion  on  ore-deposition  will 
prove  as  inspiring  to  further  investigation  as  did  Posepny's 
paper  of  1893,  and  that  data  concerning  the  possible  secondary 
enrichment  of  sulphide-ores  by  the  repetition  of  ascending 
solutions  will  be  sought  for.  There  is  nothing  like  a  working 
theory  to  sharpen  the  observation.  Theories  do  not  alter  facts, 
but  they  often  lead  us  to  find  new  ones. 

In  cordially  welcoming  the  splendid  treatise  of  Professor 
Van  Hise  I  need  make  no  reservation.  When  Posepny  made 
clear  the  essential  character  of  the  upper  or  "  vadose  "  water- 
circulation,  he  did  us  a  great  service ;  and  when  he  combated 
"  lateral  secretion  "  he  overthrew  a  very  narrow  interpretation 
of  ore-formation,  which  was  calculated  to  hinder  seriously  our 
progress  toward  the  understanding  of  these  difficult  problems. 


THE    FORMATION    OF    BONANZAS    IN   GOLD-VEINS.  755 

But  Posepny  was  carried  so  far  by  his  controversy  with  Sand- 
berger  as  to  over-emphasize  the  sole  agency  of  ascending  cur- 
rents. At  that  time,  in  1893,  I  demurred  to  this  extreme  view 
and  said,  "  the  word  circulation  is  the  key  to  the  whole  matter."* 
By  this  I  meant  that  the  entire  underground  water-circulation 
played  a  part  in  the  formation  of  ore,  and  that  to  swing  from 
one  portion  of  that  circulation  to  another,  restricting  oneself  to 
the  agency  of  either,  would  not  (so  it  seemed  to  me  from  ex- 
perience in  the  mines)  solve  the  problem. 

It  does  not  appear  to  me  that  Professor  Van  Hise  has  erred  by 
exaggerating  any  particular  view  of  the  subject.  His  elucida- 
tion of  the  water-circulation  as  a  complete  system  is  based  on  a 
broad  conception  of  the  whole  matter.  Of  course,  in  indicating 
the  work  done  by  an  agency  hitherto  largely  overlooked,  he  was 
compelled  to  place  some  emphasis  on  certain  neglected  features 
of  the  descending  portion  of  the  water-circulation,  and  thus  to 
give  it  some  prominence  in  his  masterly  analysis.  This  makes 
the  consideration  of  the  question  of  secondary  enrichments  by 
surface-waters  one  of  the  most  valuable  parts  of  his  treatise. 

Regarding  this  question  of  secondary  enrichment,  it  is  to  be 
pointed  out  that  all  ore-deposits  are  "  secondary,"  the  ore  as 
found  by  the  miner  being  merely  the  last  term  of  a  series  of 
solutions  and  precipitations  through  which  its  substance  has 
passed  in  a  constant  shifting  due  to  the  underground  water- 
circulation.  However,  the  last  stage  of  the  journey  is  the  only 
one  of  immediate  importance  to  the  miner ;  and  the  determi- 
nation of  the  causes  which  brought  it  there  is,  to  him,  far  the 
most  interesting  aspect  of  the  general  inquiry.  That  Mr.  Em- 
mons  should  also  have  investigated  and  illuminated  the 
problem  is  matter  of  much  pleasure  to  a  great  many,  engaged 
in  mining  throughout  the  West,  to  whom  his  geological  con- 
tributions have  seemed  to  possess  a  practical  bearing  and  value 
unfortunately  not  always  found  in  scientific  descriptions  of 
geological  phenomena. 

*  Trans.,  xxiv.,  950. 


48 


DISCUSSION. 

(Presented  at  the  Richmond  Meeting,  February,  1901.) 

S.  F.  EMMONS,  Washington,  D.  C. :  Papers  of  Collins,  Vogt, 
DeLaunay,  etc. — Mr.  Collins  tells  us  about  facts  in  the  veins 
of  Cornwall  that  suggest  secondary  sulphide-enrichment  is 
highly  interesting ;  and  I  am  free  to  confess  that  I  have  not 
studied  the  literature  of  that  region  as  fully  as  I  should  have 
done.  Nevertheless,  even  if  it  had  been  as  familiar  to  me  as 
it  is  to  Mr.  Collins,  I  should  probably  have  hesitated  to  draw 
theoretical  conclusions  without  having  seen  the  mines  myself; 
for  the  personal  equation  and  the  point  of  view  of  the  observer 
play,  perhaps,  a  larger  part  in  the  study  of  ore-deposits  than 
in  that  of  any  other  natural  phenomena.  One  important  pur- 
pose of  my  paper,  and  its  publication  at  the  time  of  the  Wash- 
ington meeting,  was  to  call  forth  remarks  from  other  geologists 
upon  deposits  with  which  they  were  personally  familiar,  or  to 
lead  them  to  re-examine  such  deposits  with  the  idea  of  second- 
ary enrichment  in  mind. 

Mr.  Collins's  remarks  on  Rio  Tinto,  which  he  has  the  advan- 
tage of  personally  knowing,  are  also  interesting.  With  re- 
gard, however,  to  his  suggestion — advanced  as  an  apparent  ar- 
gument against  our  theory — that  the  re-precipitation  of  copper 
from  cupric  sulphate  solution  by  pyrite  can  hardly  take  place 
there,  since  it  would  upset  the  commercial  process,  I  would 
remark  that,  while  he  is  undoubtedly  right  as  to  the  fact,  it  does 
not  militate  against  the  reduction  and  re-precipitation  of  cupric 
sulphate  in  veins ;  since  on  the  surface,  as  at  Rio  Tinto,  there 
is  free  access  of  air,  and  consequently  an  excess  of  ferric  sul- 
phate, whereas  in  depth  the  ferric  sulphate  would  have  been 
mostly  reduced  to  ferrous  sulphate,  and  (there  being  no  excess 
of  acid  to  hold  it  in  solution)  the  small  amount  of  copper  in 
the  presence  of  an  excess  of  iron  sulphide  would  be  precipi- 
tated either  as  sulphide  or  as  native  copper. 

To  Professor  Yogt's  analogous  remarks,  that  in  his  experi- 
ence sulphuric  acid  is  formed  only  in  subordinate  amount  in 
the  attack  of  sulphides  by  ferric  sulphate,  I  would  say  that  Dr. 

(756)    . 


THE    GENESIS    OF    ORE-DEPOSITS.  757 

Stokes's  experiments,  made  in  the  laboratory  of  the  U.  S.  Geo- 
logical Survey  expressly  with  a  view  to  determining  the  effects 
of  the  attack  of  ferric  sulphate  on  various  sulphides,  have 
conclusively  demonstrated  that  sulphuric  acid  is  formed  in  all 
such  attacks  in  very  considerable  amount;  much  more  than 
he  had  thought  possible  a  priori. 

It  is  highly  gratifying  that  Professor  Vogt  has  been  willing 
to  give  us  so  fully  his  views  on  the  relation  between  eruptive 
processes  and  ore-deposition,  a  subject  of  which  he  has  made  a 
most  profound  study.  His  views  and  those  of  Prof.  Van  Hise 
may  be  considered  to  express  the  opposite  poles  of  geologic 
opinion ;  the  extreme  views  of  the  European  and  American 
geologists  respectively  on  this  subject — though,  among  the  lat- 
ter, Prof.  Kemp  leans  more  to  the  European  side.  To  me  it 
seems  that  a  distinction  may  be  drawn  between  the  working 
geologists,  to  which  class  most  of  the  Americans  belong,  and 
the  professors  in  universities,  which  include  most  of  our  Euro- 
pean confreres.  The  former  are  more  apt  to  work  out  theories 
by  practical  testing  in  the  mines  themselves,  while  the  latter 
are  more  dependent  upon  the  literature  of  the  subject,  and 
therefore  upon  the  study  of  phenomena  at  second-hand,  from 
the  description  given  by  others.  Thus,  Prof.  Yogt  instances 
the  copper-mines  of  Butte  and  of  Cornwall  as  attributable  to 
magmatic*  extraction.  In  the  former  case  he  very  likely 
based  his  views  on  my  early  suggestion  (1886)  of  a  genetic 
connection  between  ore-deposition  and  the  rhyolitic  eruption  of 
the  "  Big  Butte  " ;  but  the  more  detailed  studies  which  I  have 
made  sincef  have  shown  that  the  deposits  are  earlier  than  the 
rhyolitic  eruption,  and  that  the  observed  facts  are  such  as  to 
preclude  pneumatolitic  action  as  the  source  of  the  ore  in  its 
present  condition. 

As  regards  Cornwall,  Prof.  Yogt's  process  of  reasoning  is 
that,  inasmuch  as  many  tin-deposits  have  proved  to  be  the  result 
of  magmatic  (pneumatolitic)  processes,  and  as  observations  in 
Cornwall,  as  well  as  in  the  Erzgebirge,  seem  to  show  "  that  there 
can  have  been  no  absolutely  essential  difference  between  the 

*  I  think  the  use  of  the  term  "magmatic  "  in  this  connection  very  unfortunate. 
I  presume  he  refers  to  the  pneumatolitic  method  of  extracting  the  metallic  min- 
erals from  igneous  magmas. 

t   U.  S.  Qeol.  Surv.,  Folio  38,  1897. 


758  THE   GENESIS    OF   ORE-DEPOSITS. 

genesis  of  the  cassiterite  and  that  of  the  silver-lead  veins," 
the  latter  are  to  be  attributed  to  magmatic  extraction  rather 
than  to  the  work  of  underground  water.  From  my  point  of 
view,  the  reverse  reasoning,  namely,  that  underground  water 
must  have  had  some  part  in  both  kinds  of  deposition,  is  at  least 
equally  admissible,  and  more  closely  fits  the  facts  of  nature. 

Both  Prof.  Yogt  and  Prof.  Beck  quote  in  support  of  the 
magmatic  theory  Hussak's  studies  of  the  gold-quartz  vein  of 
Passagem  in  Brazil,  which  the  latter  conceives  to  be  an  ultra- 

o  ' 

acid  granitic  apophyse.  But  both  Mr.  Lindgren*  and  myself, 
from  a  careful  consideration  of  the  facts  presented  by  Hussak, 
consider  that  he  has  proved  it  to  be  a  normal  fissure-vein,  due 
to  the  action  of  underground  waters. 

"With  regard  to  the  probable  pneumatolitic  origin  of  contact- 
deposits,  there  is  an  essential  agreement  between  Professor  Yogt 
and  Mr.  Lindgren,  as  shown  in  the  paper  presented  by  the 
latter  at  the  present  meeting,  f 

On  the  other  hand,  I  have  failed  to  recognize  the  distinction 
upon  which  both  Prof.  Vogt  and  Prof.  DeLaunay  lay  so  much 
stress,  namely,  between  older  and  younger  gold-silver  veins. 

There  can  be  no  doubt  of  the  great  value  of  such  inter- 
changes of  opinion  as  this  discussion  has  called  forth ;  and  it 
now  remains  for  each  of  us,  in  the  cases  of  difference  of  views, 
to  put  such  views  to  the  critical  test  of  further  field-studies  and 
see  how  far  the  respective  theories  are  applicable  to  the  phe- 
nomena of  nature. 

It  seems  to  me  that  the  remarks  ot  Prof.  DeLaunay,  at  the 
beginning  of  his  contribution  to  this  discussion,  may  lead  to 
misconception  with  regard  to  his  views  upon  what  we  consider 
the  essential  part  of  the  "  secondary-enrichment "  idea,  viz. : 
that  secondary  enrichment  has  undoubtedly,  and  indeed,  in 
many  cases  demonstrably  taken  place  below  the  groundwater- 
level.  For  that  reason  I  take  this  opportunity  to  quote  from 
his  last  article  in  the  Revue  Generate  des  Sciences,  entitled  "  The 
Variations  of  Metalliferous  Veins  in  Depth,"  in  which  he  ex- 
presses himself  in  more  definite  terms.  Under  the  caption, 
"  Secondary  Changes  of  Veins  in  Depth,"  after  describing  the 

*  "Metasomatic  Processes  in  Fissure-Veins,"  this  volume,  pp.  498-610. 
f  "The  Character  and  Genesis  of  Certain  Contact-Deposits,"  by  W.  Lindgren, 
Kichmond  Meeting,  February,  1901,  this  volume,  pp.  716-733. 


CHARACTER    AND    GENESIS    OF    CERTAIN    CONTACT-DEPOSITS.       759 

two  zones,  above  and  below  the  groundwater-level,  and  the  reac- 
tions that  may  go  on  there,  he  summarizes  as  follows  : 

"  A  body  situated  in  this  zone  of  permanent  waters  below  this 
hydrostatic  surface  (which  may  have  a  very  complicated  form) 
finds  itself  in  the  condition  of  a  wooden  pile,  which,  remaining 
always  immersed  in  water,  suffers  no  change.  On  the  other 
hand,  above  the  hydrostatic  surface  (the  groundwater-level) 
there  is  a  perpetual  movement  of  the  waters,  a  bringing  in,  of 
oxygen  and  carbonic  acid,  alternations  of  humidity  and  dry- 
ness,  etc. ;  it  is  there  only  that  are  produced  the  secondary  re- 
actions of  which  there  is  question  here,  and  by  which  all  the 
upper  parts  of  metalliferous  deposits  are  thoroughly  modified." 

Paper  of  Lindgren  on  "Contact-Deposits." — Mr.  Lindgren's 
paper  constitutes  a  very  valuable  and  very  practical  contribu- 
tion to  the  literature  of  ore-deposits.  It  has  long  been  my 
opinion  that  the  usage  which  prevails  among  miners,  of  calling 
so  great  a  variety  of  deposits  "  contact-deposits  "  is  bad,  because 
the  term,  as  thus  applied,  is  illogical  and  incapable  of  defini- 
tion ;  and  I  have  advocated  its  restriction  to  such  deposits  as 
occur  along  the  contact  of  eruptive  and  sedimentary  rocks. 
Mr.  Lindgren's  usage  restricts  it  still  further,  but  has  the  great 
advantage  that  it  rests  on  a  distinctly  genetic  basis.  During 
the  past  summer  I  have  had  opportunities  of  observing,  though 
not  of  studying  thoroughly,  several  deposits  which,  in  many 
respects,  fall  within  his  definition,  though  I  should  have  hesi- 
tated in  some  cases  to  call  them  contact-deposits. 

Most  of  these  deposits  were  seen  in  the  Boundary  district 
of  British  Columbia,  in  mines  lying  on  either  side  of  Bound- 
ary creek,  near  the  town  of  Greenwood.  They  constitute  the 
workable  ore-bodies  of  many  of  the  most  important  mines  of 
the  district,  such  as  the  B.  C.,  the  Knob  Hill  and  Ironsides, 
the  Mother  Lode,  and  others.  The  ores  of  these  mines  are  of 
very  low  grade,  carrying  on  the  average  from  2  to  5  per  cent, 
of  copper,  with  a  few  dollars  in  gold  per  ton.  They  occur, 
however,  in  large  bodies,  and  contain  much  lime,  iron  and 
other  bases,  with  little  sulphur,  so  that  they  can  be  mined  and 
smelted  at  an  extremely  low  cost,  By  reason  of  the  liberal 
policy  which  the  Canadian  Pacific  Railroad  has  adopted,  of 
build'ing  spurs  to  all  the  important  mines,  so  as  to  connect 


760      CHARACTER    AND    GENESIS    OF    CERTAIN    CONTACT-DEPOSITS. 

them  with  the  smelting-works,  it  is  estimated  that  the  total 
cost  of  mining  and  smelting  will  be  not  over  $5  or  $6  per 
ton. 

The  region  in  which  the  mines  occur  is  very  well  covered, 
either  by  a  luxuriant  forest  growth  or  by  glacial  drift,  often 
with  both,  so  that  outcrops  are  comparatively  rare  and  the 
geological  structure  is  correspondingly  difficult  to  decipher. 
Hence,  in  my  short  visit,  I  was  only  able  to  determine  certain 
very  broad  general  outlines. 

The  immediate  valley  in  which  the  town  of  Greenwood 
lies  is  carved  out  of  a  mass  of  light  grey,  coarsely  crys- 
talline granitic  diorite,  the  longer  axis  of  which  apparently 
runs  !N".  and  S.  with  the  valley.  As  one  ascends  the  tributary 
ravines  on  either  side,  E.  or  "W.,  one  passes  into  a  zone  of 
much  altered  greenish  rock,  called  by  the  miners  "  diorite," 
beyond  which  are  porphyries,  forming,  in  general,  the  crests  of 
the  bounding  ridges.  At  various  points  within  this  zone  are 
outcrops  of  white  crystalline  limestone ;  and  it  was  soon  found 
that  the  greater  part  of  the  so-called  "  diorite  "  is  simply  al- 
tered limestone,  being  largely  composed  of  various  normal 
contact-minerals,  the  most  prominent  of  which,  in  the  few 
specimens  gathered,  was  actinolite.  Very  likely  some  of  these 
altered  rocks  may  be  of  eruptive  origin;  as  interbedded  tuffs 
and  breccias  were  observed  at  the  Ironsides  mine,  and  dikes 
are  frequently  found  crossing  the  ore-bodies.  Such  of  the 
porphyries  as  were  examined  under  the  microscope  were  found 
to  be  of  the  syenitic  lamprophyre  type.  They  are  distinctly 
later  than  the  limestone,  cutting  it  in  dikes  and  sending 
apophyses  into  it.  The  general  impression  derived  in  going 
through  the  country  was  that  they  are  also  later  than  the 
diorite ;  but  no  contacts  were  found  which  would  afford  abso- 
lute proof  of  their  relative  age  in  this  respect. 

Compared  with  Mr.  Lindgren's  type  of  "  contact-deposits," 
the  ore-occurrences  of  this  region  show  the  following  striking 
resemblances  : 

1.  The  association  with  typical  contact-minerals,  such  as  the 
amphiboles,  garnet,  vesuvianite,  zoisite,  etc.,  and  the  evidence 
that  the  ore-minerals  were  of  nearly  contemporaneous  forma- 
tion. Mr.  Lindgren,  who  has  kindly  examined  for  me,  under 
the  microscope,  thin  sections  of  ore  from  the  Mother  Lode, 


CHARACTER    AND    GENESIS    OF    CERTAIN    CONTACT-DEPOSITS.       761 

states  that  "  they  show  pretty  clearly  that  a  metasomatic 
replacement  has  occurred,  during  which  a  granular  limestone 
has  been  converted  into  amphibolitic  rock,  and  that  simultane- 
ously, or  almost  simultaneously,  magnetite  and  sulphides  have 
been  developed." 

2.  The  association  of  magnetic  oxide  of  iron,  in  considerable 
amount,  and  of  contemporaneous  formation,  with  sulphides  of 
iron  and  copper  (more  particularly  the  latter).     This  peculiar 
association  I  had  never  had  occasion  to  observe  until  last  sum- 
mer. 

3.  The  irregular  manner  of  occurrence  of  the  ore-bodies. 
"Not  only  does  the  material  grade  off  insensibly  in  every  direc- 
tion, inwards  as  well  as  outwards,  from  the  so-called  "  ore " 
into  low-grade  rock,  but  there  are  no  fracture-planes  or  walls 
enclosing   the    ore-shoots,   or   even    defining   their   direction. 
This  constitutes  a  very  serious  element  of  uncertainty  in  the 
mining  of  such  deposits. 

4.  The  ore-bodies  are   cut  by  eruptive  dikes  which  appar- 
ently do  not  disturb  or  exert  any  metamorphic  influence  on  the 
ore,  and  yet  are  not  at  all  mineralized  themselves ;  so  that  one 
is  puzzled  to  say  whether  the  dikes  are  later  than  the  ore,  or 
the  ore  later  than  the  dikes.     In  the  B.  C.  mine,  for  instance, 
three  such  dikes  lying  in  a  nearly  horizontal  position,  and  ag- 
gregating some  90  ft.  in  thickness,  have  been  cut  in  sinking  a 
vertical  shaft  250  ft.  through  the  ore-shoot. 

On  the  other  hand,  the  definition  of  a  contact-deposit  as  in- 
volving a  close  proximity  with  an  eruptive  body  cannot  be 
regarded  at  present  as  strictly  applicable  to  these  ore-bodies. 
The  belts  of  metamorphosed  limestone  appear  to  be  from  one 
to  two  or  more  miles  wide ;  and  it  is  not  proved,  as  yet,  that 
there  are  considerable  eruptive  bodies  in  close  proximity  with 
the  respective  ore-shoots.  The  final  settlement  of  this  ques- 
tion must,  however,  await  a  detailed  geological  survey  of  the 
region. 

Another  probable  instance  of  contact-deposits  is  seen  on  the 
west  slope  of  the  Grampian  hills,  opposite  the  Horn-Silver 
mine,  in  Utah.  Here  a  monzonite  intrusion  has  broken 
through  the  dolomitic  limestone  ;  and,  along  the  contact,  there 
is  a  zone  from  a  quarter-  to  a  half-mile  wide  on  the  surface  (the 
actual  thickness  may  of  course  be  very  much  less,  dependent 


762       CHARACTER    AND    GENESIS    OF    CERTAIN    CONTACT-DEPOSITS. 

on  the  slope  of  the  contact),  of  a  reddish-brown  rock,  made  up 
largely  of  garnet,  in  which,  associated  with  veins  of  remarka- 
bly beautiful  fibrous  white  tremolite,  are  deposits  of  copper-, 
lead-  and  zinc-ores,  the  following  of  which  has  been  found  by 
the  miners  to  be  a  very  difficult  and  discouraging  matter.  I 
was  unable  to  enter  any  of  the  mines,  and  therefore  cannot 
speak  of  the  manner  of  occurrence  of  the  ore  further  than  to 
say  that  it  presents  the  peculiar  association  of  magnetite  and 
contact-minerals  with  sulphides,  mentioned  above. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.        763 

Some  Principles  Controlling  the  Deposition  of  Ores 

BY  C.    R.    VAN   HISE,    MADISON,    WIS. 

[Concluding  Contribution  of  Prof.  Van  Hise  to  the  Discussion  of  his  Paper, 
and  Others  on  the  Same  General  Subject,  presented  at  the  Washington  Meeting, 
February,  1900  (see  Trans.,  xxx.,  27,  177,  323,  424,  578)  ;  also  of  the  contribu- 
tions of  Vogt,  De  Launay,  Beck,  Lindgren,  Kemp,  Kickard,  Bain,  Keyes,  Collins 
and  Adams,  presented  at  the  Kichmond  Meeting,  February,  1901,  and  printed  in 
the  present  volume.] 

IN  June,  1900,  shortly  after  my  paper  was  published  in  the 
Transactions,  I  made  a  briefer  statement*  before  the  Western 
Society  of  Engineers  covering  the  same  ground,  which,  in  cer- 
tain respects,  is  somewhat  of  an  improvement.  For  instance, 
instead  of  using  the  terms  descending  and  ascending  with  refer- 
ence to  the  waters  resulting  in  the  two  concentrations,  my 
modified  statement  is  as  follows : 

"  The  first  concentration  of  many  ore-deposits  is  the  work  of  a  relatively  deep 
water-circulation,  while  the  reconcentration  is  the  result  of  reactions  upon  an 
earlier  concentration  through  the  agency  of  a  relatively  shallow  water-circulation. 
Commonly  the  deep  water  circulation  is  lacking  in  free  oxygen,  and  contains  re- 
ducing agents,  and  the  shallow  water  contains  free  oxygen.  The  deep  water  is 
therefore  a  reducing,  and  the  shallow  water  an  oxidizing  agent."f 

Of  the  papers  upon  ore-deposits  which,  in  vol.  xxx.  of  the 
Transactions,  follow  my  own,  or  which  were  presented  at  the 
Richmond  meeting,  a  considerable  number  are  wholly  con- 
firmatory of  the  conclusions  which  I  have  presented.  Among 
these  are  the  Washington  paper  of  Emmons  upon  the  Secondary 
Enrichment  of  Ore-Deposits;);  and  his  discussion  at  Richmond 
of  other  papers,§  that  of  Weed  upon  the  Enrichment  of  Gold 
and  Silver  Veins, ||  the  discussion  of  Emmons7,  and  at  Rich- 
mond of  Weed's  paper  by  Collinsf  and  Prof.  De  Launay,  f  the 
paper  of  Lindgren  on  Metasomatic  Processes  in  Fissure  Veins,Tf 
that  of  Rickard  upon  the  Formation  of  Bonanzas  in  the  Upper 
Portions  of  Gold  Veins,**  and  the  remarks  of  Bain  upon  the 
Mississippi  Valley  lead-  and  zinc-deposits,  ft  It  is  therefore  un- 

Jour.  of  GeoL,  vol.  viii.,  1900,  pp.  730-770.  t  Ibid.,  p.  765. 

J  This  volume,  p.  433.  \  See  under  "  Discussions  "  in  this  volume. 

||  This  volume,  p.  473.       ff  This  volume,  p.  498.       **  This  volume,  p.  734. 
tf  See  under  "  Discussions  "  in  this  volume. 


764      SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

necessary  to  discuss  these  papers ;  but  in  this  connection  those 
of  Messrs.  Emmons  and  Weed  are  of  interest,  since  their  main 
purpose  is  to  emphasize  arid  illustrate  one  of  the  principles 
stated  by  me,  which  they  have  independently  worked  out  and 
used ;  namely,  the  principle  of  secondary  concentration  by  de- 
scending waters,  not  only  in  the  belt  above  the  level  of  ground- 
water,  but  in  the  sulphide  belt  below  that  level.  This  principle, 
as  well  as  many  of  the  others  stated  in  my  paper,  I  have  been 
presenting  to  my  students  for  a  number  of  years.  Messrs. 
Emmons  and  Weed  working  at  Washington,  and  I  at  Madison, 
were  wholly  unaware  that  similar  work  was  being  done  else- 
where, and  that  identical  conclusions  had  been  reached.  If  in- 
dependent investigation  by  different  men  leading  to  the  same 
results  be  evidence  of  the  truth  of  a  conclusion,  the  principle 
of  secondary  enrichment  by  descending  waters  has  such  con- 
firmation. 

A  second  class  of  papers,  and  especially  the  admirable  papers 
of  Yogt  upon  the  Geology  of  Ore-Deposits,*  of  Lindgren  upon 
the  Character  and  Genesis  of  Certain  Contact  Deposits,f  and  a 
part  of  the  discussion  by  Prof.  Beck,  J  have  apparently  been  in- 
terpreted by  some  as  presenting  views  radically  different  from 
mine.  Two  fundamental  points  which  Lindgren,  Yogt  and 
Beck  emphasize  are  that  the  main  source  of  the  metallic  ores 
is  the  igneous  rocks,  and  that  the  heat  of  the  igneous  rocks 
has  been  instrumental  in  their  production.  With  these  posi- 
tions I  not  only  agree,  but  definitely  advocate  the  same  ideas 
in  my  paper,  as  is  shown  by  the  following  quotations : 

"  The  original  source  of  much  of  the  material  for  the  metalliferous  deposits 
may,  indeed,  be  largely  the  centrosphere  or  the  lower  part  of  the  lithosphere ; 
for  from  these  sources  vast  masses  of  volcanic,  rocks  are  injected  into  the  zone  of 
fracture  or  brought  to  the  surface.  This  is  especially  true  during  great  periods  of 
vulcanism.  Furthermore,  it  is  well  known  that  in  regions  of  volcanic  rocks  many 
ore-deposits  are  found.  Also  it  is  believed  that  all  the  rocks  of  the  lithosphere 
were  originally  igneous,  and  that  from  these  igneous  rocks  the  sedimentary  rocks 
have  been  derived  by  the  epigene  forces,  i,e.,  the  forces  working  through  the 
agencies  of  atmosphere  and  hydrosphere.  It  follows,  therefore,  that  the  metals 
of  ore-deposits,  either  directly  or  indirectly,  are  derived  from  igneous  rocks. 
However,  the  ores  are  directly  derived  from  rocks  in  the  zone  of  fracture  by  cir- 
culating underground  waters.  The  rocks  which  furnish  the  metallic  compounds 
may  be  intruded  igneous  rocks  ;  they  may  be  extruded  igneous  rocks  ;  they  may 
be  the  original  rocks  of  the  earth's  crust;  they  may  be  sedimentary  rocks  de- 

*  This  volume," p.  636.  f  This  volume,  p.  716. 

t  See  under  "Discussions"  in  this  volume. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       765 

rived  by  any  of  the  processes  of  erosion  from  primary  rocks ;  they  may  be  the 

altered  equivalents  of  any  of  these  classes."* 

****** 

"  The  nature  of  the  rocks  which  contribute  the  metallic  salts  has  been  much 
discussed.  With  Sandberger,  I  have  little  doubt  that  the  metallic  constituents  of 
ores  are  in  large  part  derived  from  the  igneous  rocks  which  have  been  intruded  or 
extruded  into  the  lithosphere  ;  and  especially  is  this  true  of  the  basic  rocks.  Le 
Conte  points  out  that  the  undoubted  frequent  occurrence  of  workable  ore-deposits 
in  regions  of  vulcanism  may  be  explained  by  the  heat  furnished  by  the  igneous 
rocks,  this  promoting  the  work  of  underground  solutions.  That  the  heat  fur- 
nished by  the  igneous  rocks  is  a  very  important  factor  in  the  production  of  ore- 
deposits,  I  have  no  doubt.  Since  it  is  very  difficult  to  prove  that  the  metallic 
content  of  an  igneous  rock  is  original,  it  is  impossible  to  make  any  general  state- 
ment as  to  whether  the  metallic  content  or  the  heat  furnished  by  the  igneous 
rocks  is  the  more  important  in  the  production  of  ore-deposits.  It  seems  to  me 
clear  that  both  are  important ;  and  equally  clear,  in  many  cases,  that  both  work 
together.  That  is  to  say,  an  igneous  rock  may  furnish  all  or  a  part  of  the  metal 
which  appears  in  an  ore-deposit,  and  the  heat  of  the  same  igneous  rock  may 
greatly  assist  its  concentration  by  the  underground  waters. 

"  While  the  massive  igneous  rocks  are  the  undoubted  source  of  a  large  portion 
of  metallic  deposits,  it  is  also  equally  certain  that  another  large  part  is  derived 
from  the  sedimentary  rocks  and  the  metamorphosed,  or  partly  metamorphosed, 
igneous  and  sedimentary  rocks.  Lastly,  it  is  also  certain  that  many  ore-deposits 
derive  their  metalliferous  content  in  part  from  igneous  rocks  and  in  part  from 
sedimentary  rocks.  Probably  this  is  the  most  frequent  of  all  cases.  To  give  any 
estimate  of  the  relative  amounts  of  metalliferous  materials  derived  from  the 
original  igneous  rocks  and  from  the  secondary  rocks  is  quite  impossible,  "f 

Prof.  Yogt  holds  that  ore-deposits  may  be  formed  by  mag- 
matic  segregation,  but  that  such  "  differentiation  "-ores  are 
"  confessedly  infrequent."!  With  this  conclusion  I  concur  in 
every  particular,  and  in  my  classification  made  a  place  for  ores 
of  this  kind:  "(A)  Ores  of  Igneous  Origin."§  Although 
agreeing  that  this  class  exists,  I  do  not  concur  in  the  conclu- 
sion that  all  of  the  ores  specifically  mentioned  by  Yogt  as  be- 
longing to  it  are  produced  by  magmatic  segregation  alone, 
without  modification  by  the  underground  water-circulation. 
Prof.  Yogt  holds,  however,  that  the  ore-deposits  formed  by 
so-called  eruptive  after-actions  are  much  more  important 
than  those  •  directly  produced  by  magmatic  segregation.  In 
this  class  of  deposits  he  places  cassiterite-veins,  apatite-veins, 
and  pegmatite-veins.  Only  the  first  of  these  groups  yields  a 
metallic  product;  and  to  the  metallic  ores  my  paper  is  con- 
fined. There  is  nothing  in  it  which  can  be  interpreted  as  dis- 

*  "Some  Principles,"  etc.,  Tram.,  xxx.,  45-46  ;  this  volume,  p.  300. 

f  This  volume,  pp.  346,  347.  t  This  volume,  p.  64i». 

2  This  volume,  pp.  284,  285,  428. 


766       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

agreeing  with  these  conclusions  of  Prof.  Vogt,  since  I  refer  to 
no  tin-deposits  whatever  as  the  product  of  underground  water, 
and  have  maintained,  as  will  be  seen  just  below,  that  the  peg- 
matite veins  are  connected  with  igneous  action. 

But  the  main  contention  of  Prof.  Vogt,  and  one  of  the  prin- 
cipal ones  of  Dr.  Lindgren,  is  that  there  is  a  large  class  of  ore- 
deposits  of  contact-metamorphic  origin.  The  existence  of  this 
class  I  have  also  distinctly  recognized.  I  say : 

"  In  another  place  I  have  explained  that  there  are  gradations  between  different 
classes  of  rocks,  and  this  statement  applies  equally  well  to  ore-deposits.  I  even 
hold  that  there  are  gradations  between  ore-deposits  which  may  be  explained 
wholly  by  igneous  agencies,  and  those  which  may  be  explained  wholly  by  the 
work  of  underground  water,  or  by  processes  of  sedimentation."* 

Also,  in  my  article  in  the  Journal  of  Geology  I  say : 

"  I  have  elsewhere  held  that  there  is  complete  gradation  between  waters  con- 
taining rock  in  solution  and  rock  containing  water  in  solution.  If  there  be  no 
sharp  separation  between  water  solutions  and  magma,  it  is  probable  that  this  is 
also  true  in  reference  to  ore-deposits  of  direct  igneous  origin  and  those  produced 
by  underground  water,  "f 

The  fact  that  I  clearly  recognize  this  class  of  deposits  is  fully 
appreciated  by  Dr.  Lindgren,  who  quotes  one  of  the  statements 
above  given,  and  also  the  following  from  my  paper  upon  North 
American  pre-Cambrian  Geology : 

"It  is  thought  highly  probable  that  under  sufficient  pressure  and  at  a  high 
temperature  there  are  all  gradations  between  heated  waters  containing  mineral 
material  in  solution  and  a  magma  containing  water  in  solution.  If  this  be  so, 
then  there  will  be  all  stages  of  gradation  between  true  igneous  injection  and 
aqueous  cementation,  and  all  the  various  phases  of  pegmatization  may  thus  be 
fully  explained."! 

It  therefore  appears  that,  so  far  as  the  classes  of  ore-deposits 
are  concerned,  there  is  no  difference  of  opinion  between  my- 
self and  Prof.  Vogt  and  Dr.  Lindgren.  We  all  agree  that  the 
class  of  contact-deposits  exists ;  that  the  source  of  the  ores  of 
such  deposits  is  largely  the  igneous  rocks ;  and  that  during  the 
concentration  of  the  ores  a  high  temperature  prevailed.  The 
difference  of  opinion  occurs  in  the  interpretation  of  particular 
cases.  Prof.  Vogt  and  Dr.  Lindgren,  but  more  especially  the 

*  This  volume,  p.  429.  f  Jour,  of  GeoL,  vol.  viii.,  1900,  p.  768. 

t  "  Principles  of  North  American  Pre-Cambrian  Geology,"  by  C.  R.  Van  Hise. 
16th  Ann.  Eept.  U.  S.  GeoL  Surv.,  Part  I.,  p.  6^7  (1895). 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OP    ORES.       767 

former,  hold  that  many  ore-deposits,  including  sulphides,  are 
more  closely  allied  to  the  igneous  rocks  than  to  water-deposits ; 
while  I  hold  that  the  majority  of  ores,  and  especially  those  in- 
cluded under  «  Other  Contact-Deposits  "  by  Yogt,*  as  shown 
by  their  character  and  relations,  are  deposited  by  underground 
waters.  However,  I  have  distinctly  recognized  that  there  may 
be  deposits  in  which  it  is  difficult  to  say  which  of  these  two 
agencies  predominate.  For  instance,  in  the  Journal  of  Geology 
I  say  : 

"  There  may  be  ore-deposits  in  which  water-action  and  magmatic  differentiation 
have  been  so  closely  associated  that  one  cannot  say  whether  the  resultant  ore- 
deposit  is  mainly  a  water-deposit  or  mainly  a  magmatic  deposit,  "f 

But  in  the  vast  majority  of  cases  I  hold  that  there  is  little 
difficulty  in  discriminating  between  veins  and  dikes — the  first 
representing  crystallizations  from  water-solutions ;  the  second, 
crystallization  from  magma.  There  are  few  cases  where  the 
discrimination  with  reference  to  ore-deposits  is  not  easy.  While 
gradations  between  water-deposited  ores  and  igneous  ores  are 
uncommon,  gradations  between  the  different  classes  of  ore-de- 
posits formed  by  underground  water  are  common. 

Concerning  pneumatolytic  action  as  an  auxiliary  in  the  for- 
mation of  ores,  as  held  by  Vogt,  Lindgren,  Beck  and  Kemp,  I 
do  not  deny  the  existence  of  ores  of  this  class,  but  simply  say 
that,  while  ore-deposits  produced  by  this  process  are  theoreti- 
cally possible,  and  very  likely  exist,  I  do  not.  know  of  any  in- 
stance in  which  it  has  been  shown  that  pneuraatolytic  action  has 
actually  been  a  dominating  factor  in  the  production  of  a  work- 
able ore-deposit.  However,  I  think  it  not  unlikely  that  pneu- 
matolytic action  (in  the  sense  of  water-gas  under  very  high 
pressure,  above  the  critical  temperature  of  water)  may  have 
helped  in  the  segregation  of  the  metals  by  transporting  them 
to  the  main  channels  of  water-circulation.  This  condition  of 
the  water  I  distinctly  recognizej  as  producible  not  only  by 
igneous  rocks,  but  also  by  dynamic  action.  But  discrimina- 
tion should  be  made  between  what  may  be  true  and  what  has 
been  shown  to  be  true.  The  presence  of  such  so-called  con- 
tact-minerals as  tourmaline  and  fluorite,  holding  such  elements 

*  This  volume,  pp.  650,  651,  652,  653. 

f  Jour,  of  GeoL,  vol.  viii.,  1900,  p.  768.  }  This  volume,  p.  293. 


768       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

as  boron  and  fluorine,  is  not  proof  that  they  and  the  other  min- 
erals in  the  veins  containing  them  were  not  deposited  by  heated 
circulating  waters. 

From  the  proposition  that  igneous  rocks  are  an  important 
source  of  the  ores,  and  that  the  ores  are  extracted  from  them 
by  circulating  waters,  it  by  no  means  necessarily  follows  that  this 
work  is  chiefly  done  while  the  rock  is  a  fused  liquid  mass. 
After  the  rocks  crystallize  and  become  partly  cooled,  deforma- 
tion, and  the  cooling  itself,  may  produce  many  fractures  in 
them,  thus  furnishing  channels  through  which  the  hot  waters 
course  while  they  are  collecting  the  metals.  In  this  manner  is 
largely  explained  the  difficulty  under  which  Prof.  Kemp  labors 
in  understanding  how  circulating  waters  may  work  upon  hot 
igneous  rocks.*  So  far  as  igneous  rocks  are  deep-seated  intru- 
sives,  they  may  retain  after  crystallization  a  very  large  part  of 
the  water  which  they  previously  held.  This  is  evidenced  by 
the  innumerable  liquid  inclusions  in  many  such  rocks. 

In  this  connection  I  may  say  that,  among  the  papers  pre- 
sented in  this  discussion,  Lindgren's  admirable  paper  upon 
metasomatic  processes  in  fissure-veins  seems  to  me  wholly  to 
confirm  the  view  that  the  deposition  of  most  metallic  deposits 
is  effected  by  underground  water.  The  metasomatic  changes  in 
the  rocks  which  Dr.  Lindgren  describes  occur  not  only  in  the 
veins  themselves,  but  in  the  walls  of  the  veins.  Moreover,  in 
many  cases  the  amount  of  change  decreases  in  passing  from  the 
walls  into  the  veins.  During  the  metasomatic  changes,  metals 
were  added  and  subtracted.  Lindgren  declares  that,  in  the 
great  majority  of  these  cases,  the  chief  agents  through  which 
the  metasomatic  changes  were  accomplished  were  circulating 
waters.  He  says : 

"  The  processes  observed  are  such  as  can  only  be  explained  by  aqueous  agencies. 
Possible  exceptions  are  the  forms  of  alteration  connected  with  cassiterite,  apatite, 
and  tourmaline  veins,  in  which  pneumatolytic  conditions  may  have  partly  ob- 
tained, "f 

He  concludes,  further,!  that  the  waters  were  probably  hot; 
that  those  which  originally  deposited  the  sulphide  constituents 
were  probably  ascending;  but  that  the  ascending  waters  are 
chiefly  of  surface-origin.  Therefore,  in  all  these  matters,  by 

*  This  volume,  pp.  687,  688,  etc.  f  This  volume,  p.  610. 

J  This  volume,  p.  610. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       769 

his  exhaustive  study  of  the  metasomatic  processes  in  the  veins, 
Dr.  Lindgren  fully  confirms  my  most  fundamental  contentions! 
It  is  noteworthy  that  Prof.  Yogt  and  Dr.  Lindgren,  with  ad- 
mirable scientific  restraint,  notwithstanding  the  beliefs  which 
they  hold,  discriminate  clearly  between  the  few  cases  in  which 
they  have  shown  a  probability  that  the  ores  are  the  products  of 
igneous  action  and  the  far  more  numerous  cases  in  which  the 
evidence  of  such  origin  is  very  scanty  or  wanting  altogether. 
Says  Prof.  Vogt  : 

"That  the  ore-deposits  first  mentioned  above,  viz.,  the  titanic  iron-ores  in  gab- 
bro,  the  chromite-oceurrences  in  peridotites,  the  nickel-pyrrhotite  deposits  in 
gabbro,  etc. ,  were  formed  by  magmatic  extraction,  I  think  I  have  scientifically 
proved  beyond  doubt ;  and  I  believe  that  the  magmatic-extraction  theory  advanced 
for  the  cassiterite-  and  apatite-veins  is  in  its  main  proposition  correct.  For  the 
ore-deposits  subsequently  considered,— the  contact-deposits,  the  pyritic  deposits, 
the  gold-veins,  silver-lead  veins,  copper-ore  veins,  etc.,— the  views  here  offered 
become  confessedly  more  and  more  hypothetical.  But  they  have  much  in  their 
favor;  and  even  if,  following  in  particular  the  French  observers,  I  have  here 
ascribed  to  magmatic-extraction  too  great  a  significance,  I  believe,  nevertheless, 
that  the  hypothesis  is  worthy  of  thorough  scientific  discussion."* 

Thus  Prof.  Yogt  recognizes  clearly  that  the  attribution  of  the 
larger  class  of  these  ores  to  igneous  action  is  purely  hypothet- 
ical. He  fully  appreciates  that,  of  the  great  majority  of  ore- 
deposits,  he  has  wholly  failed  to  show  that  igneous  agencies 
have  separated  the  ores  from  the  original  rocks  and  placed  them 
in  their  present  positions.  This  connection  must  be  made  be- 
fore the  hypothesis  advanced  by  Prof.  Yogt  can  hope  for  ac- 
ceptance. Since  the  majority  of  the  ore-deposits  thought  by 
Prof.  Yogt  to  be  possibly  due  to  "  contact  after-action  "  in  some 
other  sense  than  segregation  by  underground  water  differ  in 
no  essential  particulars  as  to  their  character,  the  minerals  they 
contain,  the  relations  of  these  minerals  to  one  another,  the  re- 
lations of  the  ores  and  minerals  to  the  surrounding  rocks,  the 
presence  of  crustification,  and  other  features,  from  ore-deposits 
which  many  authorities,  including  Prof.  Yogt,  recognize  as  de- 
posited by  underground  water,  I  shall  hold  to  the  old  view  that 
they  are  the  results  of  water-deposition  until  evidence  is  pre- 
sented showing  the  contrary.  To  attempt  to  prove  the  propo- 
sition that  these  ores  are  deposited  by  water  would  require  the 

*  This  volume,  p.  658. 


770       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

repetition  throughout  of  the  arguments  for  such  an  origin 
which  have  been  presented  during  the  past  half-century  by 
nearly  all  of  the  famous  men  who  have  discussed  ore-deposits. 
If  these  arguments  are  not  adequate  to  convince  the  reader,  I 
cannot,  in  closing  this  discussion,  present  the  case  more  fully, 
but  must  defer  the  matter  until  the  publication  of  my  treatise 
upon  Metamorphism,  in  which  I  consider  much  more  fully  the 
circulation  and  work  of  underground  water,  and  the  character 
of  the  deposits  produced  by  that  agent. 

If  it  be  recognized  that,  in  the  majority  of  the  cases  cited 
by  Yogt  and  Lindgren,  the  materials  of  the  ores  were  trans- 
ported and  deposited  in  their  present  positions  by  underground 
waters,  it  makes  no  difference  to  me  whether  such  ore-deposits 
be  called  contact-deposits,  hydro-thermal  deposits,  dynamo- 
metamorphic  deposits,  or  regional  metamorphic  deposits,  as 
proposed  by  Lindgren.* 

As  I  have  pointed  out,f  dynamic  action  may  increase  the 
temperature  of  the  underground  waters,  and  make  the  condi- 
tions much  more  favorable  for  the  deposition  of  ores.  If  in  the 
first  part  of  my  paper,  discussing  general  principles,  I  have  not 
made  clear  my  belief  in  the  extreme  efficiency  of  hot  water,  as 
compared  with  that  of  cold  water,  in  the  segregation  of  ores,  I 
have  failed  altogether  to  convey  my  ideas.  I  fully  recognize 
the  remarkable  relative  potency  of  hot  water  in  all  classes  of 
alterations  of  rocks,  including  the  deposition  of  ores.  I  em- 
phasize especially  the  effect  of  high  temperature,  (1)  in  pro- 
ducing a  deeper  circulation,^  (2)  in  producing  a  more  rapid 
circulation,!  and  (3)  in  very  greatly  increasing  the  power  of 
water  to  do  chemical  work  of  all  kinds.  For  instance,  I  say : 

"  But  pure  water  at  a  high  temperature  is  a  potent  solvent.  Barus  has  shown 
that  water  at  temperatures  above  185°  C.  attacks  the  silicates  composing  soft  glass 
with  astonishing  rapidity.  At  180°  C.  various  zeolites  can  be  dissolved  in  pure 
water,  the  material  crystallizing  out  on  cooling.  Lemberg  shows  that  water  at 
210°  C.  slowly  dissolved  anhydrous  powdered  silicates.  It  is  therefore  apparent 
that  water  in  the  lower  part  of  the  zone  of  fracture  is  a  most  potent  chemical 
agent.  "|| 

With  this  conclusion  the  following  quotation  shows  that 
Prof.  Yogt  agrees  : 

*  This  volume,  pp.  730,  731.  f  This  volume,  304. 

J  Ibid.,  298.  §  Ibid.,  303-306.  II  Ibid.,  308. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       771 

"  As  is  well  known,  the  ionization  of  water  increases  rapidly  with  its  tempera- 
ture. This  explains  the  activity  of  water  at  high  temperatures.  Thus,  for  ex- 
ample, Barns  has  shown  that  water  heated  above  185°  C.  attacks  the  silicates 
composing  soft  glass  with  astonishing  rapidity  ;  and  an  experiment  by  Lemberg 
has  proved  that  water  at  210°  C.  slowly  dissolves  anhydrous  powdered  silicates."* 

Further,  I  strongly  make  the  point  that  both  the  speed  of 
solution  and  the  amount  of  material  which  may  be  taken  into 
solution  are  greatly  increased  by  high  temperature ;  f  and  in 
proof  of  the  efficacy  of  hot  water  in  the  production  .of  ore- 
deposits,  I  cite  the  Cordilleran  region  of  the  West!  as  one  in 
which  the  temperature  of  the  water  is  higher  than  normal,  and 
in  which  ore-deposits  are  common. 

In  conclusion  as  to  this  portion  of  the  discussion,  I  would  say 
that,  while  I  think  I  have  given  adequate  weight  to  igneous  rocks 
as  a  source  of  the  ores,  and  to  the  resultant  hot  waters  as  an 
agency  in  their  concentration,  I  have  not  elaborated  that  branch 
of  the  subject.  The  reason  is,  that  these  ideas  are  not  new, 
but  have  been  generally  accepted  for  decades  by  all  who  have 
written  upon  ore-deposits.  A  complete  treatise  upon  ore- 
deposits  should,  of  -course,  give  proportional  representation  to 
all  parts  of  the  subject;  but  a  paper  on  the  subject  necessarily 
covers  the  new  ground  most  fully ;  and  if,  in  addition  to  this,  it 
put$  new  material  in  its  proper  relations  and  proportions  to  old 
material,  that  is  all  that  can  be  fairly  expected. 

I  have  reserved  for  separate  consideration  most  of  the  points 
raised  in  Prof.  Kemp's  paper  upon  "  The  Role  of  the  Igneous 
Rocks  in  the  Formation  of  Veins," §  with  the  arguments  and 
conclusions  of  which  I  am  not  in  such  general  agreement  as 
with  those  of  the  other  papers  named.  I  shall  state  the  points 
both  of  agreement  and  of  difference  between  us ;  and,  I  need 
hardly  say,  with  entire  personal  esteem  and  respect  for  Prof. 
Kemp.  But  my  position  is  rendered  somewhat  embarrassing 
by  the  circumstance  that  this  contribution  closes  the  discussion, 
so  far  as  it  is  to  be  published  by  the  Institute  in  the  special 
volume  now  in  press. 

1.  From  the  frequent  occurrence  of  ore-bodies  in  regions  of 
vulcanism,  it  does  not  follow,  as  held  by  Prof.  Kemp,||  that  the 

*  This  volume,  p.  643.  f  Ibid.,  320,  321.  %  Ibid.,  304,  305. 

g  This  volume,  pp.  681-709.  ||  This  volume,  pp.  686,  708,  709. 

49 


772       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

igneous  rocks  are  the  sole  source,  or,  in  some  cases,  even  an 
important  source  of  the  ores.  As  pointed  out  by  Prof.  Le 
Conte  many  years  ago,  and  as  shown  by  me  in  my  paper 
(Trans.,  xxx.,  91,  92),  "the  undoubted  occurrence  of  workable 
ore-deposits  in  regions  of  vulcanism  may  be  explained  by  the 
heat  furnished  by  the  igneous  rocks,  this  promoting  the  work 
of  the  underground  solutions."  I  have  already  emphasized  the 
enormously  increased  activity  of  solutions  with  rise  of  tempera- 
ture. In  the  neighborhood  of  igneous  rocks  the  underground 
solutions  are  hot,  and  these  hot  solutions  may,  and  in  many 
cases,  I  believe,  undoubtedly  do,  derive  a  large  part  of  their 
metallic  material  from  the  sedimentary  or  metamorphosed 
rocks,  although,  as  indicated  in  my  original  paper,*  I  maintain 
that  probably  the  ultimate  source  of  all  the  ores,  and  very  fre- 
quently the  chief  or  sole  immediate  source,  has  been  the  igneous 
rocks. 

2.  While  Prof.  Kemp  would  derive  the  majority  of  ores  from 
igneous  rocks,  he  declaresf  that  surface-flows   of  such  rocks 
are  unfavorable  to  vein-formation.     But,  to  give  an  instance 
to  the  contrary,  the  Lake  Superior  copper-deposits  were  shown 
by  Pumpelly,  years  ago,  to  occur  in  or  associated  with  surface 
volcanic  rocks.     I  think  the  true  statement  is,  that  in  most  dis- 
tricts very  recent  volcanic  flows  have  not  had  time  enough  for 
the  development  of  contained  or  connected  ore-deposits;   or 
else,  they  have  not  been  eroded  deeply  enough  to  expose  such 
deposits,  if  they  exist.    But  in  the  San  Juan  region  of  Colorado, 
where  denudation  has  taken  place  on  a  vast  scale  in  very  late 
geological  time,  great  ore-deposits    do  occur  in  Tertiary  vol- 
canic rocks ;  and  it  would  be  rash  to  say  that  ore-deposits  are 
not  even  now  forming  in  the  middle  and  lower  parts  of  the 
great  lava-flows  of  the  plateaus  of  the  West.     Indeed,  I  think 
it  highly  probable  that  such  formations  are  going  on,  and  that 
at  some  future  period  the  resulting  ore-deposits  will  be  at  the 
surface. 

3.  In  asserting  the  existence  of  gradations  between  pegma- 
tite and  quartz-veins,  I  am  glad  to   find  Prof.  Kemp  in  full 
accord  with  me.     I  pointed  out  such  gradations  some  years  ago, 
and,  as  already  explained,  advanced  as  the  explanation  that 

*  This  volume,  pp.  300,  301.  t  This  volume,  p.  695. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OP    ORES.       773 

water  and  rock,  at  sufficiently  high  temperatures  and  pressures, 
are  miscible  in  all  proportions. 

4.  From  Prof.  Kemp's  statement*  that  "  practically  all  stu- 
dents of  volcanic  phenomena  are  agreed  that  steam  and  its  dis- 
sociated representatives  in  the  molten  rock  are  the  chief,  if  not 
the  only,  cause  of  eruption,"  I  must  wholly  dissent,  holding  with 
Duttonand  Gilbertf  that,  in  areas  of  regional  vulcanism  (which 
are  those  containing  the  most  extensive  ore-deposits),  gravita- 
tive  stress  is  the  dominant  force  producing  eruption,  although 
it  is  agreed  that  steam  plays  a  subordinate  part,  and  an  im- 
portant part  in  local  vulcanism. 

5.  Perhaps  I   do  not  fully  appreciate  Prof.   Kemp's  argu- 
mentsj   concerning  capillary  attraction  as  connected  with  the 
movements    of   underground   water.      Prof.  Kemp    says   that 
the  imperviousness  of  strata   is   partly  due   to   the  "  feeble- 
ness  or  disappearance  of   capillary    attraction   with   increase 
of   pressure."      On    later    pages   he    says :    "  Whenever,   for 
example,    capillary   transmission    occurs,   the    previously   ac- 
quired head  is  lost,  and  the  emerging  water  proceeds  on  its 
way  only  under  a  newly  accumulating  head."     Further,  he 
says  that  "  capillary  attraction  is  largely  an  ascensive  force." 
I    am    uncertain    whether    or    not   Prof.    Kemp    intends    to 
imply  that  I  have  advocated  the  view  that  capillarity  is  an 
important  force  which  accounts  for  the  circulation  of  ground- 
water  in  the  belt  of  saturation.     As  a  matter  of  fact,  I  have 
not   appealed    to  the   force  of   capillarity  in   any  way  what- 
ever to  explain  the   circulation  in  this  belt.     It  seems  to  me 
that  Prof.  Kemp  has  wholly  failed  to  recognize  the  great  differ- 
ence in  the  nature  and  forces  which  control  the  circulation  of 
water  in  the  belt  of  weathering,  above   the  level  of  ground- 
water,  and  the  belt  of  cementation,  below  that  level. §     Above 
the  level  of  groundwater  the  force  of  capillarity  is  important  in 
the  movement  of  groundwater.     This  matter  I  shall  discuss 
fully  in   my  treatise  on  Metamorphism,  but  cannot  take  up 

*  This  volume,  p.  687. 

t  "  Geology  of  thedigh  Plateaus  of  Utah,"  by  C.  E.  Button,  Rept.  of  U.  S. 
Geogr.  and  Oeol.  Surv.  of  the  Rocky  Mt.  Region,  Washington,  1880,  pp.  113-142. 

"Geology  of  the  Henry  Mts.,"  by  G.  K.  Gilbert ;  Id.,  pp.  66-74. 

"Earth-Movements,"  by  C.  E.  Van  Hise.  Trans.  Wis.  Acad.  Sci.  Arts  and 
Letters,  vol.  xi.,  1898,  pp.  495-502. 

J  This  volume,  pp.  699,  701-2,  705,  708.     \  See  my  remarks,  this  volume,  p.  327. 


774       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

here,  as  it  is  a  complicated  one.  Below  the  level  of  ground- 
water,  the  size  of  the  openings,  as  I  have  fully  explained,*  is 
of  very  great  importance  in  the  movement  of  the  underground 
water,  because  friction  runs  up  very  rapidly  with  subdivision 
of  the  openings;  but  how  capillarity  is  a  "  descensive  "  or  "  as- 
censive  "  force  in  this  belt,  I  am  at  a  loss  to  understand. 

6.  Prof.  Kemp  does  me  an  unintentional  injustice  when  he 
cites  me  as  supporting  "  the  view  that  hot  springs  are  the 
result  of  normal  terrestrial  circulations,  without  accessions  of 
heat  other  than  those  which  would  be  received  through  the 
ordinary  increase  of  temperature  with  depth. "f   I  refer  the  in- 
crease of  temperature  of  the  underground  waters  to  the  normal 
increase  of  temperature  with  depth,  to  vulcanism,  and  to  dynamic 
action.^     Regional  vulcanism  and  orogenic  movements  I  men- 
tion twice  as  producing  high  temperature. 

7.  But  I  held,  and  still  hold,  that  difference  in  temperature 
of  the  ascending  and  descending  columns  is   a  cause  which 
works  in  the  promotion  of  circulation  as  an  adjunct  to  the  main 
cause,  head.     Prof.  Kemp§   argues  against  this  conclusion  in 
the  following  way : 

"  (3)  That  water  under  great  load  or  pressure  does  not  expand  according  to 
the  4  per  cent,  rate  named  (i.e.,  4  per  cent,  for  100°  C.).  On  the  contrary,  it 
may  be  held  by  the  pressure  at  fixed  volume,  despite  the  added  heat.  If,  for  ex- 
ample, we  roughly  assume  a  column  of  water  1  sq.  in.  in  cross-section  and  2  ft. 
high  (it  is  really  about  2  ft.  3^  in.)  as  equal  to  a  pressure  of  a  pound  to  the  square 
inch,  in  10,000  ft.  we  would  have  a  pressure  of  something  near  5000  Ibs.,  or  over  2 
tons  to  the  square  inch  ;  and  in  the  face  of  this,  the  expansion  of  water  from  an 
added  temperature  of  100°  C.  practically  becomes  a  negligible  quantity  as  con- 
tributing to  hydrostatic  head." 

This  argument  seems  to  me  to  be  unsound  for  the  following 
reasons : 

a.  Since  I  emphasize  vuicanism  and  orogenic  movements  as 
chief  causes  of  high  temperature  in   underground  water,  the 
depth,  and  therefore  the  pressure,  may  be  but  a  small  fraction 
of  that  assumed  by  Prof.  Kemp. 

b.  The  only  experiments  which  I  have  found  upon  the  com- 
pressibility of  water  at  high  temperature  are'those  of  Barus,|| 

*  See  my  remarks,  Trans.,  xxx.,  40-45.  f  This  volume,  p.  704. 

t  Trans.,  xxx.,  49.  $  This  volume,  p.  704. 

||  "The  Compressibility  of  Colloids,"  by  C.  Barus ;  Am.  Journ.  of  Sci.,  4th 
ser.,  vol.  vi.,  1898,  pp.  287-289. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       775 

in  which  he  finds  that  the  compression  resulting  from  the  pres- 
sure cited  by  Kemp  is  much  less  than  would  be  necessary  to 
neutralize  the  expansion  due  to  the  heat  mentioned. 

c.  Admitting  for  the  moment  that  the  pressure  does  neutralize 
the  expansion  due  to  heat,  since  the  pressure  is  nearly  the  same 
upon  both  the  ascending  and  descending  columns,  and  inasmuch 
as,  under  the  hypothesis,  there  is  a  difference  in  temperature  be- 
tween the  two  columns,  there  would  be  a  difference  in  density, 
and  therefore  a  cause  for  flowage. 

8.  Upon  another  point  connected  with  the  circulation  of  un- 
derground water,  Prof.  Kemp  says  : 

1 '  (4)  We  must  bear  in  mind  also  that  the  standing  body  of  cold  groundwater  fills 
the  interstices  of  all  rocks  near  the  surface,  except  those  in  very  arid  regions,  and 
exerts  a  retarding  influence  on  uprising  currents."* 

I  am  entirely  at  a  loss  to  understand  how  the  coldness  of  the 
water  prevents  circulation  due  to  difference  in  head  and  differ- 
ence in  temperature  of  the  two  columns,  except  as  to  an  effect 
which  I  have  emphasized, f  namely,  that  due  to  varying 
viscosity. 

After  the  arguments  above  mentioned,  Prof.  Kemp  says : 

' '  I  regard  it  as  extremely  improbable  that  the  water  of  any  natural  spring 
whose  flow  is  due  simply  to  hydrostatic  head,  has  ever  reached  more  than -a  very 
limited  depth  below  the  point  of  emergence."! 

We  have  already  found  that  difference  in  temperature  of  the 
descending  and  ascending  columns  are  excluded  by  Prof. 
Kemp  as  an  effective  cause  of  deep  circulation.  The  force  to 
which  he  appeals  to  explain  the  deep  circulation  is  that  which 
proceeds  from  the  igneous  rocks.  He  says : 

' '  I  will  even  go  so  far  as  to  say  that  it  is  in  the  highest  degree  improbable  that 
any  waters  which  have  reached  depths  even  approximating  10,000  ft.  can  ever 
again  reach  the  surface  and  yield  flowing  springs,  except  through  the  propulsion 
of  stores  of  energy  contributed  by  still  heated  masses  of  igneous  rock."g 

I,  of  course,  maintain  that  the  heat-energy  of  the  igneous 
rocks  passes  into  and  thereby  expands  the  water,  thus  caus- 
ing a  difference  in  density  between  the  ascending  and  de- 
scending columns, ||  and  thereby  promoting  circulation.  But 

*  This  volume,  p.  704.  f  Trans.,  xxx.,  43.  I  This  volume,  p.  705. 

\  This  volume,  p.  705.  II  Trans.,  xxx.,  47-49. 


776          SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

Prof.  Kemp  has  just  thrown  this  use  of  the  energy  of  the 
igneous  rocks  out  of  consideration ;  and  how  this  energy  acts 
in  producing  a  circulation,  unless  it  be  by  heating  and  thereby 
expanding  the  water,  he  does  not  explain. 

9.  Prof.  Kemp  says--  that  "  standing  water  in  abandoned 
shafts  is  strong  evidence  of  the  impenetrability  of  rocks."* 
This  seems  to  me  untenable.  Such  standing  water  has  come  in 
either  from  the  surface,  or  through  the  "  impenetrable  rocks." 
The  latter  hypothesis  Prof.  Kemp  rejects.  But  if  the  former 
be  true,  why  does  not  the  water  rise  with  periodic  additions  ? 
According  to  my  view,  standing  water  in  shafts,  exactly  as  in 
wells,  indicates  the  upper  limit  of  the  belt  of  saturation.  But 
the  standing  water  maintains  its  uniform  level  (in  the  absence 
of  pumping)  by  flowage  through  the  rocks,  compensating  the 
local  additions  or  subtractions.  Certainly  the  water  standing 
in  the  wells  of  the  drift-covered  regions  of  North  America  does 
not  prove  that  there  is  no  active  underground  circulation  in 
the  drift. 

Passing  from  specific  points  concerning  the  circulation  of 
underground  water,  I,  of  course,  largely  dissent  from  Prof. 
Kemp's  general  view  upon  this  subject,  and  can  only  refer  to 
the  argument  already  given  in  my  paper. f  If  the  evidence 
there  presented,  showing  that  the  main  source  of  the  under- 
ground water  depositing  the  ores  is  meteoric,  and  not  de- 
rived from  the  igneous  rocks,  as  held  by  Prof.  Kemp  (but 
without  giving  adequate  evidence),  does  not  prove  the  point,  it 
is 'useless  further  to  discuss  the  matter  here.  In  my  treatise  on 
Metamorphism  I  shall  cover  this  part  of  the  subject  much  more 
exhaustively.  While  I  hold  that  the  main  source  of  the  water 
depositing  ores  is  meteoric,  I  recognize  that  another  source  of 
such  water  is  the  igneous  rocks.  I  say : 

"  Also,  through  the  agency  of  vulcanism,  water  occluded  in  magma  is  trans- 
ferred from  the  zone  of  rock  flowage,  or  even  possibly  from  the  centrosphere,  to 
the  zone  of  rock-fracture. "  J 

Nor  am  I  able  to  accept  Prof.  Kemp's  statements  as  to  the 
small  amount  and  local  deficiency  of  ground  water.  He  says, 
"  In  regions  when  the  rainfall  is  small,"  .  ..."  if  the  rocks 

*  This  volume,  p.  709.  f  Ibid.,  pp.  282-334.  t  Ibid.,  p.  302. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       777 

are  shattered,  standing  groundwater  maybe  entirely  lacking."* 
And  again,  "  The  groundwater  may  entirely  fail  in  arid  re- 
gions, "f  I  know  of  no  region  in  the  United-  States  which 
justifies  these  statements. 

While  I  have  never  advocated  a  universal  uniform  under- 
ground circulation,  as  implied  by  Prof.  Kemp,  I  have  held,  and 
still  hold,  that  the  amount  of  underground  water  and  its  cir- 
culation is  much  more  general  than  he  believes.  This  problem 
may  be  considered,  first,  from  the  point  of  view  of  the  amount 
of  underground  water  now  present ;  and  second,  and  more  im- 
portant, the  amount  of  work  which  has  been  done  by  under- 
ground water. 

Upon  the  first  point,  it  is  contended  by  Prof.  Kemp  that  the 
amount  of  underground  water  in  the  belt  of  saturation  is  usu- 
ally small ;  but  in  opposition  to  this  view  we  have  the  general 
experience  of  mining  men  and  of  those  who  by  wells  seek  under- 
ground water.  While  there  are  notable  exceptions,  it  is  in 
general  a  difficult  and  expensive  process  to  lower  artificially 
the  level  of  groundwater  which  is  generally  found  in  both 
humid  and  arid  regions,  though  at  greater  depth  in  the  latter. 
In  the  lead-  and  zinc-districts  of  Missouri,  this  operation,  called 
by  the  miners  "  beating  the  water,"  is  usually  attempted  only 
by  a  number  of  companies,  acting  jointly,  and  constitutes  the 
most  formidable  part  of  mining-work. 

In  Wisconsin,  it  is  a  grave  hindrance  to  mining  below  water- 
leve].  The  lowering  of  the  groundwater  by,  say,  50  ft.,  is  an 
exceedingly  difficult  task,  involving  enormous  expenses  for 
pumping.  The  subsequent  holding  of  the  water  at  a  given 
level  is  much  easier,  as  Prof.  Kemp  has  noted.  But  my  con- 
clusions from  these  facts  are  that,  in  the  belt  of  saturation,  the 
openings  are  large  and  the  quantity  of  water  is  great,  but  the 
circulation  is,  in  most  cases,  not  too  rapid  to  be  controlled  by 
pumps  of  moderate  capacity — although,  in  some  cases,  to  hold 
the  water  at  a  given  level  involves  the  handling  of  vast  quan- 
tities of  underground  water. 

In  this  connection  Prof.  Kemp  remarks!  that  the  circulation 
at  smaller  depths  than  1500  or  2000  ft.  has  no  bearing  on  the 
question  of  ore-deposition.  While  a  few  ore-deposits  have 

*  This  volume,  p.  706.         f  This  volume,  p.  709.         J  This  volume,  p.  699. 


778       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

been  profitably  worked  to  a  greater  depth  than  this,  it  is  well 
known  that  probably  more  than  90  per  cent,  of  the  metallic 
wealth  of  the  earth  yet  mined  has  come  from  above  the  2000-ft. 
level  ;  and  therefore  there  is  no  warrant  for  the  statement  that 
the  circulation  above  this  level  is  not  of  vital  importance  in 
the  production  of  ore-deposits. 

In  this  matter  of  depth,  Prof.  Kemp  asserts,*  of  the  general 
circulation  of  underground  water,  that  "  something  like  2000 
ft.  appears  to  be  its  limit;"  but  the  only  evidence  which  he 
presents  upon  this  point  is  that  in  some  cases  this  is  the  fact. 
The  local  instances  cited  are  not,  to  my  mind,  proof  of  such  a 
law.  On  the  other  hand,  the  evidence  which  I  have  presented 
to  the  contrary  is  reinforced  by  the  arguments  of  Prof.  Vogt,f 
which,  combining  the  facts  of  observed  depth  of  denudation  of 
veins  with  the  likeness  of  their  deeper  parts  to  those  parts 
nearer  the  surface  plainly  produced  by  underground  waters, 
clearly  lead  to  the  conclusion  that,  in  many  cases,  the  under- 
ground circulation  must  have  been  efficient  to  a  depth  several 
times  greater  than  2000  ft. 

On  the  second  point,  the  work  of  underground  water,  Prof. 
Kemp  declares  that  veins  are  the  exceptional,  not  the  general, 
work  of  this  agency.  He  says  that  while  veins  occur  locally 
in  mining  districts,  there  is  a  "  general  absence  of  veins."  J  If 
Prof.  Kemp  means  mineral  veins,  this  is  of  course  true;  but  if 
he  means  literally  what  he  says  (and  it  is  only  with  this  mean- 
ing that  any  argument  can  be  made  as  to  the  circulation  of  un- 
derground water),  I  wholly  dissent  from  the  conclusion.  In  my 
field-work  throughout  the  United  States  and  considerable  areas 
of  Canada  I  have  yet  to  find  a  district  in  which  a  series  of  rocks 
has  been  in  the  belt  of  saturation  for  a  long  time  geologically  in 
which  there  are  not  extensive,  metasomatic  changes  in  the 
rocks,  and  many  veins.  For  instance,  in  the  Appalachian  re- 
gion, almost  innumerable  veins,  the  work  of  underground 
water,  maybe  seen  from  Maine  to  Alabama;  but  only  very 
rarely  and  locally  are  there  important  ore-deposits.  Therefore 
the  localization  of  mineral  (i.  e.,  ore-bearing)  veins  gives  no  in- 
formation as  to  the  general  circulation  of  underground  water. 

While  I  repeat  that  I  have  never  advocated  a  universal,  uni- 

*  This  volume,  p.  699.  f  This  volume,  p.  669  et  seq. 

This  volume     .  70. 


,     .        . 
This  volume,  p.  707. 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       779 

form,  vigorous  underground  circulation,  as  implied  by  Prof. 
Kemp,  I  have  held  and  still  hold  that,  almost  universally,  in 
those  places  where  ore-deposits  occur,  a  vigorous  circulation  was 
going  on  during  the  time  the  ores  were  deposited ;  and  at  the 
only  places  of  which  I  know  where  ore-deposits  are  now  form- 
ing, such  a  circulation  is  going  on.  The  fact  that  some  areas 
in  which  ore-deposits  are  now  worked  do  not  now  show  a  vigor- 
ous circulation  has  no  bearing  upon  the  question  of  the  depo- 
sition of  these  ores  by  underground  water.  The  very  process 
of  vigorous  circulation  by  underground  water  results  in  the 
cementation  of  the  openings,  as  I  have  fully  explained.*  In  so 
far  as  the  innumerable  openings  are  filled,  and  during  the  pro- 
cess here  and  there  ore-deposits  are  formed,  just  to  that  extent 
the  openings  are  closed.  When  the  openings  have  been  filled 
to  such  an  extent  that  they  become  subcapillary,  circulation 
practically  ceases  for  the  time.  But  subsequent  earth-move- 
ments or  igneous  intrusions  may  again  produce  openings  in  the 
rocks,  and  thus  a  new  circulation  may  be  set  up.  Of  course  it 
is  well  known  that  in  the  deep  copper-deposits  of  the  Lake 
Superior  region,  and  at  various  other  localities,  as  at  Przibram, 
there  is  not  now  a  vigorous  underground  circulation.  I  cannot 
believe  that  Prof.  Kemp  therefore  dissents  from  the  conclusion 
of  Pumpelly,  Irving,  and  others,  that  in  the  Lake  Superior '  re- 
gion the  deposits  of  copper  in  the  openings  of  the  conglomerates 
and  amygdaloids,  extending  to  a  depth  of  5000  ft.  or  more,  are 
the  cementation-result  of  circulating  underground  waters. 
Posepny  realized  full  well  that  when  the  ore-deposits  were 
formed  at  Przibram,  there  was  a  vigorous  circulation  of  under- 
ground waters  at  a  depth  below  1100  meters.  With  regard  to 
the  formation  of  the  deep  deposits  of  Lake  Superior,  Przibram, 
and  many  other  localities  in  all  parts  of  the  world,  cited  by 
Posepny,  in  some  of  which  there  is  now  but  a  feeble  circula- 
tion, I  am  but  a  follower  of  Sandberger  and  Posepny  and 
nearly  all  the  eminent  geologists  who  have  written  upon  ore- 
deposits,  in  the  belief  that  these  ores  were  put  in  place  by  un- 
derground waters.  In  whatever  respects  I  may  differ  from 
Sandberger  or  Posepny,  there  is  absolute  identity  in  our  funda- 
mental contention  that  the  great  majority  of  the  metallic  ores, 

*  This  volume,  pp.  326-334. 


780       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

to  the  greatest  depth  penetrated  by  man,  were  deposited  in  the 
places  where  they  now  exist  by  circulating  underground  waters. 
Probably  Prof.  Kemp  does  not  intend  to  argue,  although  his 
reasoning  could  be  so  interpreted,  that  because  there  is  not  at 
present  a  vigorous  circulation  where  ore-deposits  exist,  such  ores 
were  not  deposited  by  the  circulation  of  underground  water. 

While  it  is  clear  that  the  underground  circulation  is  much 
more  vigorous  and  widespread  than  is  believed  by  Prof.  Kemp, 
and  while  I  first  discuss  the  circulation  which  would  take  p]ace 
in  a  homogeneous  medium,*  I  follow  with  what  I  regard  as 
one  of  the  most  essential  points  of  my  paper,  viz.,  the  elaborate 
evidence  presented  of  the  very  unequal  and  variable  character 
of  the  underground  water-circulation,  due  to  unequal  tempera- 
ture caused  by  normal  increase,  vulcanism  and  dynamic  action  ; 
the  preferential  use  by  water  of  large  channels  ;f  the  variation 
of  the  rocks  in  porosity  and  structure ;  the  complexity  and  ir- 
regular distribution  of  the  openings ;  the  intersections  of  frac- 
tures; the  successions  of  fractures;  the  impervious  strata  at 
various  depths;  the  pitching  troughs  and  arches;  etc.J  Prof. 
Kemp  speaks  §  also  of  the  importance  of  impervious  strata  in 
influencing  the  circulation  of  ground  water.  I  have  strongly 
emphasized ||  the  very  profound  influence  of  impervious  strata 
upon  the  deposition  of  ores,  and  have  explained  that  the  differ- 
ence between  pervious  and  impervious  strata  is  that  pervious 
strata  have  openings  of  capillary  or  supercapillary  size,  while 
the  openings  of  impervious  strata  are  subcapillary. 

The  localization  of  ore-deposits,  of  which  Prof.  Kemp  speaks,^ 
I  have  shown  to  be  due  to  the  fact  that  each  case  of  the  for- 
mation of  a  deposit  "  requires  the  fortunate  combination  of 
many  favorable  factors  working  harmoniously  together,  the 
absence  of  any  one  of  which  may  prevent  the  concentration  of 
the  ore-deposit,"**  Only  here  and  there  have  existed  the  re- 
markable combination  of  circumstances  necessary  to  form  an 
ore-deposit,  and  thus  once  in  a  million  times,  or  once  in  ten 
million  times,  a  vein  formed  carries  a  sufficient  amount  of  the 
valuable  metals  to  be  an  ore. ft 

*  This  volume,  pp.  306-315.  f  Ibid.,  315-317.  J  Ibid.,  393-427. 

\  This  volume,  p.  699.  ||  Ibid.,  396-416. 

f  This  volume,  p.  708.  **  This  volume,  p.  421. 

tf  See  my  article,  Jour,  of  Geol.,  vol.  viii.,  1900,  p.  753. 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       *781 

Therefore,  notwithstanding  the  contrary  belief  of  Prof. 
Kemp,  I  again  assert  that  the  deposition  of  the  great  majority 
of  ore-deposits — namely,  those  produced  by  underground  water 
— is  a  special  case  of  the  general  work  of  underground  water, 
which  can  only  be  adequately  explained  by  a  profound  knowl- 
edge of  the  facts  and  principles  controlling  the  circulation  and 
work  of  underground  water,  and  a  detailed  knowledge  of  the 
special  modifications  necessary  to  explain  the  localization  and 
relations  of  the  ores. 

In  closing  this  discussion  I  must  express  deep  gratification 
for  the  kindly  and  appreciative  manner  in  which  my  attempt 
to  solve  some  of  the  problems  of  ore-deposition  has  been  re- 
ceived by  the  men  who  have  discussed  it.  Indeed,  the  papers 
of  Lindgren,  Vogt,  Beck  and  Rickard  speak  of  the  paper  in 
a  more  complimentary  way  than  I  could  have  hoped.  When 
I  published  it,  I  anticipated  that  it  would  be  regarded  as  too 
theoretical  by  geologists  who  are  at  work  in  the  field  upon  the 
fascinating  problem  of  ore-deposition,  and  especially  by  the 
practical  men  who  are  in  charge  of  the  development  of  large 
mining  properties.  In  this  respect,  however,  I  have  been 
wholly  mistaken ;  for  the  most  hearty  appreciation  which  has 
come  to  me  has  been  from  these  two  classes  of  men. 

In  conclusion,  I  can  only  say  that  I  find  in  the  various  papers 
following  my  own  so  much  which  confirms  my  conclusions 
(and  no  reason  which  appears  to  me  to  be  sound,  advanced 
against  any  of  them)  that,  after  a  careful  consideration  of  all 
that  has  been  said,  I  find  it  unnecessary  to  modify  my  paper 
(beyond  the  changes  in  the  Journal  of  Geology  to  which  I  have 
referred)  either  as  to  statements  of  facts  and  conclusions,  or  as 
to  their  proportional  importance. 


APPENDIX. 

SECRETARY'S  NOTE. — The  amount,  variety  and  value  of  the 
contributions  made  to  the  science  of  ore-deposits  by  the  Amer- 
ican Institute  of  Mining  Engineers,  since  its  organization  in 
1871,  may  be  inferred  from  the  list,  given  below,  of  papers  in 
its  Transactions  bearing  upon  that  subject.  This  list  does  not 
include  the  numerous  papers  on  coal,  or  other  non-metallic  de- 
posits, such  as  those  of  clay,  apatite,  bauxite,  etc.  On  the 
other  hand,  it  comprises,  besides  many  treatises  directly  treat- 
ing of  the  formation  of  ore-deposits,  and  many  generalizations 
of  great  suggestiveness  as  to  parts  of  that  field,  a  large  number 
of  studies  of  single  mines  or  districts,  in  which  geological  and 
mineralogical  facts  of  importance  are  incidentally  reported, 
though  greater  space  is  often  given  to  methods  of  mining,  etc. 
As  a  whole,  I  venture  to  say,  this  list  presents  a  mass  of  care- 
ful observations  and  intelligent  deductions  which  no  student 
of  this  science  can  afford  to  disregard. 

Papers  in  the  Transactions  of  the  American  Institute  of  Mining 

Engineers,  Bearing  Directly  or  Indirectly  upon  the 

Science  of  Ore-Deposits. 

TITLE.  VOL.     PAGE 

The  Geographical    Distribution   of    Mining   Districts   in    the 

United  States.     By  R.  W.  Raymond, I.      33 

The  Origin  of  Metalliferous  Deposits.     By  T.  Sterry  Hunt,       .  I.     413 

The  Ore  Knob  Copper-Mine  and  some  Related  Deposits.     By 

T.  Sterry  Hunt,      . II.     123 

The  Formation  of  Fissures  and  the  Origin  of  their  Mineral 

Contents.     By  A.  J.  Brown, II.     215 

The  Magnetic  Iron-Ores  of  New  Jersey  ;  their  Geographical 

Distribution  and  Geological  Occurrence.     By  J.  C.  Smock,  II.     314 

The  Ores  of  Iron  ;  their  Geographical  Distribution  and  Rela- 
tion to  the  Great  Centers  of  the  World's  Iron  Industries. 
By  Henry  Newton, III.  380 

On  the  Occurrence  of  the  Brown  Hematite  Deposits  of  the  Great 

Valley.     By  Frederick  Prime,  Jr., III.     410 

The  Cornwall  Iron-Mine  and  some  Related  Deposits  in  Pennsyl- 
vania. By  T.  Sterry  Hunt, IV.  319 

The  Southeastern  Missouri  Lead-District.  By  G.  C.  Broad- 
head,  V.  100 

(782) 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       783 

TITLE.  VOL.     PAGE 

A  Study  of  the  Specular  and  Magnetic  Iron-Ores  of  the  New 

Eed   Sandstone   in   York  County,  Pa.     By   Persifor  Fra- 
zer, Jr., V.     132 

The  Nickel-Ores  of    Orford,  Quebec,  Canada.     By  W.  E.  C. 

Eustis, VI.     209 

The   Mesozoic   Formation   in  Virginia.     By  Oswald  J.  Hein- 

rich, VI.     227 

The   Eureka   Lode  of   Eureka,    Eastern   Nevada.     By  W.    S. 

Keyes, VI.     344 

What  is  a  Pipe-Vein  ?     By  R.  W.  Raymond,       ....  VI.     393 

Missing  Ores  of  Iron.     By  Persifor  Frazer,  Jr. ,          .        .        .  VI.     531 

The  Ore  Deposits   of  Eureka  District,    Eastern  Nevada.     By 

William  P.  Blake, VI.     554 

The  Antimony-Deposits  of  Arkansas.  By  Charles  E.  Wait,  .  VIII.  42 
Silver  Islet.  By  Thomas  Macfarlane,  .  .  .  .  .  VIII.  226 
The  Gold-Gravels  of  North  Carolina.  By  W.  C.  Kerr,  .  .  VIII.  462 
The  Silver  Sandstone  District  of  Utah.  By  Charles  M.  Rolker,  IX.  21 
Some  Copper-Deposits  of  Carroll  County,  Maryland.  By  Per- 
sifor Frazer, IX.  33 

The  Whopper  Lode,  Gunnison  County,  Colorado.     By  Persifor 

Frazer, .  IX.     249 

Auriferous  Slate-Deposits  of  the  Southern  Mining  Region.     By 

P.  H.  Mell,  Jr.,     .        .        .     '  .    '" IX.     399 

The    Gold-Bearing    Mispickel- Veins    of    Marmora,    Ontario, 

Canada.     By  R.  P.  Rothwell, IX.     409 

The  Formation  of  Gold  Nuggets  and  Placer-Deposits.     By  T. 

Egleston, . '     V   ,     *  IX.     633 

On  the  Occurrence  of  Lustrous  Coal  with  Native  Silver  in  a 

Vein  in  Porphyry  in  Ouray  County,  Colorado.     By  G.  A. 

Koenig  and  Moritz  Stockder,         .        .  .        .        .  IX.     650 

Note  on  Black-Band   Iron-Ore   in  West  Virginia.     By  S.  P. 

Sharpless, X.       80 

The  Geology  and  Veins  of  Tombstone,  Arizona.     By  William 

P.  Blake, X.     334 

The  Gold- Fields  of  the  Southern  Portion  of  the  Island  of  San 

Domingo.     By  R.  P.  Rothwell, X.     345 

The  Mines  and  Mills  of  Gilpin  County,  Colorado.     By  A.  N. 

Rogers, XL       29 

On   the  Peculiar  Features  of  the   Bassick  Mine.     By  L.   R. 

Grabill, XL     110 

Notes  on  the  Geology  and  Mineralogy  of  San  Juan  County,  Col- 
orado.    By  Theodore  B.  Comstock, XL     165 

The  Iron-Ores    of    the   Middle    James    River.      By   Persifor 

Frazer, XL     201 

Coal  and  Iron  in  Alabama.     By  T.  Sterry  Hunt,         ...  XL     236 

The  Iron-Ores  of  the  Valley  of  Virginia.     By  A.  S.  McCreath,  XII.       17 

The  Copper- Deposits  of  the  South  Mountain.     By  C.  Hanford 

Henderson, '      •  «        •        •  XII.       85 

Geologico-Geographical  Distribution  of   the  Iron-Ores  of  the 

Eastern  United  States.     By  John  C.  Smock,         .        . 
Some  Canadian  Iron-Ores.     By  Frederick  P.  Dewey,         .        .  XII.     192 


784       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 

TITLE.  VOL.     PAGE 

The  Pyrites-Deposits  of  Louisa  County,  Virginia.     By  W.  H. 

Adams, XII.     527 

Note  on  Tantalite  and  other  Minerals,  Accompanying  the  Tin- 
Ore  in  the  Black  Hills.     By  Charles  A.  Schaeffer,       .        .  XIII.     231 
The  Vallecillo  Mines,  Mexico.  *  By  Richard  E.  Chism,      .        .  XIII.     351 
Geology  and  Mineral  Resources  of  the  Rio  Grande  Region  in 

Texas  and  Coahuila.     By  E.  J.  Schmitz,      ....  XIII.     388 

The  Electrical  Activity  of  Ore-Bodies.     By  Carl  Barus,     .        .  XIII.     417 

The  Iron-Mines  of  Putnam   County,    N.    Y.     By   Arthur  F. 

Wendt, XIII.     478 

The  Iron-Ores  of   Pictou   County,    Nova   Scotia.     By  E.  Gil- 
pin,  Jr., XIV.       54 

The  Geology  and  Mineral  Resources  of  Sequatchee  Valley,  Ten- 
nessee.    By  W.  M.  Bowron, XIV.     172 

The  Sulphide  Deposit  of  South  Iron  Hill,  Leadville,  Colorado. 

By  Francis  T.  Freeland, XIV.     181 

The   " Centennial"   and   "Lotta"  Gold  Properties,  Coahuila, 

Mexico.     By  Persifor  Frazer, XIV.     196 

Note  on  an  Exhibition  of  Banded  Structure  in  a  Gold-Vein. 

By  Charles  M.  Rolker,  .       '  .• XIV.     265 

Notes  on  Certain  Iron-Ore-Deposits  in  Colorado.     By  Charles 

M.  Rolker, XIV.     266 

Notes  on  the  Leadville  Ore-Deposits.     By  Charles  M.  Rolker. 

(See  correction,  p.  948 ), XIV.     273 

Note  on  the  Apatite  Region  of    Canada.     By  Dr.   T.   Sterry 

Hunt, XIV.     495 

The  Nova  Scotia  Gold-Mines.     By  E.  Gilpin,  Jr.,      .        .        .  XIV.     674 

Geology  of  the  Low-Moor,  Virginia,  Iron-Ores.     By  Benjamin 

Smith  Lyman, XIV.     801 

Iron-Ore  Deposits  of  Southern  Utah.     By  William  P.  Blake,    .  XIV.     809 

The  Cornwall  Iron-Ore  Mines,  Lebanon  County,  Pennsylvania. 

By  E.  V.  D'Invilliers,  .         .      .  .,       .        .         .        .        .  XIV.     873 

The  Copper-Ores  of  the  Southwest.     By  Arthur  F.  Wendt,        .  XV.       25 

Notes  on  the  Geology  of  the  Tilly  Foster  Ore-Body,  Putnam 

County,  N.  Y.     By  Ferdinand  S.  Ruttmann,        .        .         .  XV.       79 
The  Genesis  of  Certain  Ore-Deposits.     By  S.  F.  Emmons,         .  XV.     125 
The  Diamond  Mines  of  South  Africa.     By  Gardiner  F.  Wil- 
liams,    .        .        .        ..       .• XV.     392 

Sierra  Mojada,  Mexico.     By  Richard  E.  Chism,         ...  XV.     542 

Indicative  Plants.     By  R.  W.  Raymond, XV.     645 

Mining  Developments  on  the  Northwestern  Pacific  Coast  and 

their  Wider  Bearing.     By  Amos  Bowman,  ....  XV.     707 

The  Silver-Mines  of  Calico,  California.     By  Waldemar  Lind- 

gren, XV.     717 

Gold  and  Silver  Mining  in  Utah.     By  O.  J.  Hollister,       .        .  XVI.         3 

The  Old  Telegraph  Mine,  Utah.     By  G.  Lavagnino, .        .        .  XVI.       25 

Notes  on  the  Geology  of  Butte,  Mont.     By  S.  F.  Emmons,        .  XVI.       49 

The  Association  of  Minerals  in  the  Gagnon  Vein,  Butte  City, 

Montana.     By  Richard  Pearce, XVI.       62 

The  Rainbow   Lode,   Butte  City,   Montana.     By    William  P. 

Blake, v  .        .         .  XVI.       65 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       785 


TITLE. 

The  Chapin  Iron-Mine,  Lake  Superior.     By  Per  Larsson,  . 

Mode  of  Deposition  of  the  Iron-Ores  of  the  Menominee  Kange, 
Michigan.  By  John  Fulton, 

The  Bedded  Ore-Deposits  of  Ked  Mountain  Mining  District, 
Ouray  County,  Colorado.  By  G.  E.  Kedzie, 

Notes  on  the  Topography  and  Geology  of  the  Cerro  de  Pasco, 
Peru.  By  A.  D.  Hodges,  Jr., 

Notes  on  the  Topography  and  Geology  of  Western  North  Caro- 
lina.— The  Hiawassee  Valley.  By  Henry  E.  Col  ton,  .v  , 

Hot  Springs  Formation  in  Ked  Mountain  District,  Colorado  :  A 
Reply  to  the  Criticism  of  Mr.  Emmons.  By  Theodore  B. 
Comstock, ,  .  .  .  '  i 

Notes  on  the  Kosario  Mine  at  San  Juancito,  Honduras,  C.  A. 
By  Thomas  H.  Leggett,  v  .  .  .  ^  . 

The  Copper-Deposits  of  Copper  Basin,  Arizona,  and  their 
Origin.  By  William  P.  Blake,  .  .  *  .  .  ,.  . 

Ore-Deposits  of  the  Black  Hills  of  Dakota.  By  Franklin  B. 
Carpenter,  ..  .  .  .  .  .  .  .„ 

The  Distribution  of  Phosphorus  in  the  Ludington  Mine,  Iron 
Mountain,  Michigan  :  A  Study  in  Isochemic  Lines.  By 
David  H.  Browne,  .  .  .  ;.».,.  < 

The  Ore  Deposits  of  Red  Mountain,  Ouray  County,  Colorado. 
By  T.  E.  Schwarz,  ....  .  .  .  ... 

The  Geology  and  Ore-Deposits  of  Iron  Hill,  Leadville,  Colo- 
rado. By  A.  A.  Blow,.  f  •  „  .-  .  .  \  •*.  .  i  „ 

The  Geological  Relations  of  the  Principal  Nova  Scotia  Min- 
erals. By  E.  Gilpin,  Jr.,  .  '  .  .  .  .  » 

Notes  on  the  Geology  of  the  DeKaap  Gold-Fields  in  the  Trans- 
vaal. By  W.  H.  Furlonge,  .  .  .  .  .  « 

The  Association  of  Gold  with  Other  Metals  in  the  West.  By 
Richard  Pearce,  .  .  .  ...  .  .  -  . 

Gold-Quartz.     By  W.  M.  Courtis, 

The  Iron-Ores  of  the  United  States.     By  T.  Sterry  Hunt, .      •  v 

Geological  Notes  on  the  Manganese  Ore-Deposit  of  Crimora, 
Virginia,  By  Charles  E.  Hall, 

The  Mount  Morgan  Mine,  Queensland.     By  T.  A.  Rickard, 

Notes  on  the  Iron-Ores  of  Danville,  Pennsylvania,  with  a  De- 
scription of  the  Long-Wall  Method  of  Mining  Used  in 
Working  Them.  By  H.  H.  Stock,  .  .  . 

The  Bendigo  Gold-Field.     By  T.  A.  Rickard,    . 

Zinc-Blende  Mines  and  Mining  near  Webb  City,  Mo.  By  Carl 
Hemich, »  .  .  .  •'• 

La  Gardette :  The  History  of  a  French  Gold-Mine.     By  T.  A.  • 
Rickard,         .         .        ~i        .         * 

Association  of  Apatite  with  Beds  of  Magnetite.  By  William 
P.  Blake, 

A  New  Tin  Mineral  in  the  Black  Hills.     By  Titus  Ulke,   . 

The  Late  Discovery  of  Large  Quantities  of  Magnetic  and  Non- 
Magnetic  Pyrites  in  the  Croton  Magnetic  Iron-Mines.  By 
W.  H.  Hoffman, 

The  Mesabi  Iron-Range.     By  Horace  V.  Winchell,   . 


VOL.       PAGE 

XVI.  119 

XVI.  525 

XVI.  570 

XVI.  729 

XVI.  839 

XVII.  261 

XVII.  432 

XVII.  479 

XVII.  570 

XVII.  616 

XVIII.  139 

XVIII.  145 

XVIII.  198 

XVIII.  334 

XVIII.  447 

XVIII.  639 

XIX.  3 

XX.  46 

XX.  133 

XX.  369 

XX.  463 

XXL  3 

XXI.  79 

XXI.  159 

XXL  240 


XXI.     513 
XXI.     644 


786       SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES. 


TITLE.  VOL.     PAGE 

The  Bendigo  Gold-Field  (Second   Paper)  :  Ore-Deposits  Other 

than  Saddles.     By  T.  A.  Rickard, XXI.     686 

The  Cause  of  Faulting.     By  John  A.  Church,    ....  XXI.     782 

Notes  on  the  Geology  of  the  Half-Moon  Mine,  Pioche,  Nevada. 

By  Ernest  Wiltsee, XXI.     867 

The  Biwabik  Mine.     By  H.  V.  Winchell  and  J.  T.  Jones,         .  XXI.     951 

Geological  Distribution  of  the   Useful   Metals  in  the  United 

States.     By  S.  F.  Emmons.     (See  Discussion,  p.  732),         .          XXII.       53 

The  Lead-  and  Zinc-Deposits  of  the  Mississippi  Valley.     By 

Walter  P.  Jenney.     (See  Discussion,  p.  621),       .        .        .  XXII.     171 

On  a  Kemarkable  Deposit  of  Wolfram-Ore  in  the  United  States. 

By  Adolf  Gurlt, XXII.     236 

The  Origin  of  the  Gold-Bearing  Quartz  of  the  Bendigo  Keefs, 

Australia.     By  T.  A.  Kickard.     (See  Discussion,  p.  738),  .          XXII.     289 

The  Bertha  Zinc-Mines  at  Bertha,  Va.     By  William  H.  Case. 

(See  Discussion,  p.  696), XXII.     511 

The  Mineral  Deposits  of  Southwest  Wisconsin.     By  William  P. 

Blake, .  XXII.     558 

The  Genesis  of  Ore-Deposits.  By  F.  Posepny.  (See  Discus- 
sion, p.  587), XXIII.  197 

The  Silver-Mines  of  Lake  Valley,  New  Mexico.    By  Ellis  Clark,         XXIV.     138 

The  Allotropism  of  Gold.     By  Henry  Louis,      ....         XXIV.     182 

The  Zinc  Ore-Deposits  of  Southwestern  New  Mexico.  By  Wil- 
liam P.  Blake. XXIV.  187 

Iron-Ores  of  East  Texas.     By  W.  Kennedy.     (See  Postscript, 

p.  862), XXIV.     258 

The  Geological  Structure  of  the  Ringwood  Iron  Mines,  New 

Jersey.     By  Frank  L.  Nason, XXIV.     505 

Notes  on  the  Structure  of  the  Franklinite-  and  Zinc-Ore  Beds 

of  Sussex  County,  New  Jersey.     By  William  P.  Blake,       .         XXIV.     521 

The  Ore-Deposits  of  Butte  City.     By  K.  G.  Brown,   .        .        .         XXIV.     543 

The  Nickel-Mine  at  Lancaster  Gap,  Pennsylvania,  and  the 
Pyrrhotite-Deposits  at  Anthony's  Nose,  on  the  Hudson. 
ByJ.  F.Kemp.  (See  Discussion,  p.  883),  .  .  .  XXIV.  620 

Lead-   and  Zinc-Deposits  of  Missouri.     By  Arthur  Winslow. 

(See  Discussion,  p.  931), XXIV.     634 

The  Mines  of  the  Chalanches,  France.     By  T.  A.  Kickard,       .         XXIV.     689 

Cinnabar  in  Texas.     By  William  P.  Blake,         ....  XXV.       68 

The  Tin-Deposits  of  Durango,  Mexico.     By  Walter  Renton  In- 

galls.     (See  Discussion,  p.  997), XXV.     146 

The  Ducktown  Ore- Deposits,  and  the  Treatment  of  the  Duck- 
town  Copper-Ores.  By  Carl  Henrich, XXV.  173 

Hysteromorphous  Auriferous  Deposits  of  the  Tertiary  and  Cre- 
taceous Periods  in  New  Zealand.  By  Henry  A.  Gordon,  .  XXV.  292 

The  Form  of  Fissure- Walls,  as  Affected  by  Sub-Fissuring  and 

by  the  Flow  of  Kocks.     By  William  Glenn,         .        .        .          XXV.     499 

The  Gold-Regions  of  Georgia  and  Alabama.     By  William  M. 

Brewer, XXV.     569 

The  Geological  Structure  of  the  Western  Part  of  the  Ver- 
million  Range,  Minnesota.  By  Henry  Lloyd  Smyth  and  J. 
Ralph  Finlay, XXV.  595 


SOME    PRINCIPLES    CONTROLLING    DEPOSITION    OF    ORES.       787 


TITLE. 

The  Present  Condition  of  Gold-Mining  in  the  Southern  Appa- 
lachian States.  By  H.  B.  C.  Nitze  and  H.  A.  J.  Wilkens. 
(See  Discussion,  p.  1016), 

The  Ore-Deposits  of  the  Australian  Broken  Hill  Consols  Mine, 
Broken  Hill,  New  South  Wales.  By  George  Smith,  . 

Copper-Ores  in  the  Permian  of  Texas.  By  W.  J.  Schmitz. 
(See  Discussion,  p.  1051), 

Vein- Walls.     By  T.  A.  Kickard.     (See  Discussion,  p.  1053),    . 

Gold  in  Granite  and  Plutonic  Kocks.     By  William  P.  Blake,    . 

Sketch  of  a  Portion  of  the  Gunnison  Gold-Belt,  including  the 
Vulcan  and  Mammoth  Chimney-Mines.  By  Arthur  Lakes, 

The  Smuggler-Union  Mines,  Telluride,  Colorado.  By  J.  A. 
Porter, 

Gold  in  the  Guyanas.     By  Henry  G.  Granger,    .        .        ;••'•,..' 

The  Ore-Shoots  of  Cripple  Creek.     By  Edward  Skewes,     . 

Some  Mines  of  Kosita  and  Silver  Cliff,  Colorado.  By  S.  F. 
Emmons, 

The  Occurrence  and  Treatment  of  Certain  Gold-Ores  of  Park 
County,  Colorado.  By  B.  Sadtler,  .  .  .  ;  . 

The  Occurrence  of  Gold-Ores  in  the  Eainy  Kiver  District,  On- 
tario, Canada.  By  William  Hamilton  Merritt,  . 

The  Enterprise  Mine,  Kico,  Colorado.     By  T.  A.  Kickard, 

The  Manganese- Deposits  of  the  Department  of  Panama,  Colom- 
bia. By  Eduardo  J.  Chibas,  <.  . 

The  Geology  of  the  Magnetites  near  Port  Henry,  N.  Y.,  and 
Especially  those  of  Mineville.  By  J.  F.  Kemp,  . 

The  Chromite-Deposits  on  Port  au  Port  Bay,  Newfoundland. 
By  George  W.  Maynard,  .  ....  .  .  »* 

The  Potsdam  Gold-Ores  of  the  Black  Hills  of  South  Dakota. 
By  Frank  Clemes  Smith,  .  .  .  .  .,•..>.  .' 

Some  Dike-Features  of  the  Gogebic  Iron-Range.  By  C.  M. 
Koss.  (Discussion,  p.  978), 

The  Genesis  of  Certain  Auriferous  Lodes.  By  John  R.  Don. 
(Discussion,  p.  993),  .  ...  .  » 

The  Origin  and  Mode  of  Occurrence  of  the  Lake  Superior  Cop- 
per-Deposits. By  M.  E.  Wadsworth, 

The  Kotchkar  Gold-Mines,  Ural  Mountains,  Russia.  By  H.  B. 
C.  NitzeandC.  W.  Purington.  (Discussion,  p.  844), 

Mining  Districts  of  Colombia.  By  Henry  G.  Granger  and  Ed- 
ward B.  Treville.  (Discussion,  p.  803  ;  see  also  p.  591),  . 

Kalgoorlie,  Western  Australia,  and  its  Surroundings.  By 
George  J.  Bancroft.  (Discussion,  p.  808),  .  .  ;  .. 

Notes  on  the  Vein-Formation  and  Mining  of  Gilpin  County, 
Colo.  By  Forbes  Rickard,  .  .  .  .... 

The  Manganese-Ore  Industry  of  the  Caucasus.  By  Frank 
Drake.  (Postscript,  p.  841 ), 

Emery,  Chrome-Ore  and  Other  Minerals  in  the  Villayet  of 
Aidin,  Asia  Minor.  By  W.  F.  A.  Thomae, 

Note  on  Limonite  Pseudomorphs  from  Dutch  Guiana.  By  R. 
W.  Raymond, .  .  , 

The  Auriferous  Deposits  of  Siberia.     By  Rene  de  Batz,     . 

50 


VOL.  PAGE 

XXV.  661 

XXVI.  69 

XXVI.  97 

XXVI.  193 

XXVI.  290 

XXVI.  440 


XXVI.  449 

XXVI.  516 

XXVI.  553 

XXVI.  773 

XXVI.  848 

XXVI.  853 

XXVI.  906 

XXVII.  63 

XXVII.  146 

XXVII.  283 

XXVII.  404 

XXVII.  556 

XXVII.  564 

XXVII.  669 

XXVIII.  24 

XXVIII.  33 

XXVIII.  88 

XXVIII.  108 

XXVIII.  191 

XXVIII.  208 

XXVIII.  235 

XXVIII.  452 


788      SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES. 


TITLE.  VOL.    PAGE 

The  Alluvial  Deposits  of  Western  Australia.  By  T.  A. 

Kickard, XXVIII.  490 

Notes  on  the  Mines  of  the  Frontino  and  Bolivia  Company, 
Colombia,  S.  A.  By  Spencer  Cragoe.  (Discussion,  p. 
908;  see  also  pp.  33,  803),  XXVIII.  591 

The  Superficial  Alteration  of  Western  Australian  Ore-Deposits. 

By  Herbert  C.  Hoover, XXVIII.  758 

The  Platinum-Deposits  of  the  Tura  Kiver-System,  Ural  Moun- 
tains, Kussia.  By  C.  W.  Purington, XXIX.  3 

The  Occurrence,  Origin  and  Chemical  Composition  of  Chromite, 
with  Especial  Keference  to  the  North  Carolina  Deposits. 
By  J.  H.  Pratt,  .....  .  .  .  .  .  XXIX.  17 

The  Gold-Bearing  Veins  of  Bag  Bay,  near  Lake  of  the  Woods. 

By  Peter  McKellar, XXIX.  104 

Notes  on  the  Geology  of  Sonora,  Mexico.     By  E.  T.  Dumble,  .         XXIX.     122 

The  Kich  Patch  Iron  Tract,  Virginia.     By  H.  M.  Chance,         .         XXIX.     210 

Modern  Gold-Mining  in  the  Darien.  Notes  on  the  Reopening  of 

the  Espiritu  Santo  Mine  at  Cana.  By  Ernest  E.  Woakes,  XXIX.  249 

The  Liberty  Bell  Gold-Mine,  Telluride,  Colorado.  By  Arthur 

Winslow, XXIX.  285 

Iron-Ores  of  the  Potsdam  Formation  in  the  Valley  of  Virginia. 

By  Charles  Catlett, "...  XXIX.  308 

The  Copper-Deposits  of  Vancouver  Island.  By  William  M. 

Brewer, XXIX.  483 

The  Mines  and  Mill  of  the  Atacama  Mineral  Company,  Ltd. , 

Taltal,  Chili.  By  Sidney  H.  Loram, XXIX.  488 

The  Copper  Queen  Mine,  Arizona.  By  James  Douglas.  (Dis- 
cussion, p.  1056), XXIX.  511 

The  Peculiar  Ore-Deposit  of  the  East  Murchison  United  Gold- 
Mine,  Western  Australia.  By  D.  P.  Mitchell,  .  .  .  XXIX.  556 

The  Manganese-Deposits  of  Bahia  and  Minas,  Brazil.  By  John 

C.  Branner, XXIX.  756 

Some  Principles  Controlling  the  Deposition  of  Ores.  By  C.  E. 

VanHise, XXX.  27 

The  Secondary  Enrichment  of  Ore-Deposits.  By  S.  F.  Em- 

mons,  .  .  .  . .:-•"  XXX.  177 

A  Peculiar  Clastic  Dike  near  Ouray,  Colorado,  and  its  Asso- 
ciated Deposit  of  Silver  Ore.  By  F.  L.  Eansome,  .  .  XXX.  227 

Some  Notes  on  the  Nome  Gold  Eegion  of  Alaska.  By  F.  C. 

Schrader  and  Alfred  H.  Brooks, XXX.  236 

Notes  on  the  Gold-Mines  of  Zarnma,  Ecuador.  By  J.  Ealph 

Finlay, XXX.  248 

Gold-Ores  of  the  Black  Hills,  South  Dakota.  By  H.  M. 

Chance, XXX.  278 

Origin  and  Classification  of  Ore-Deposits.  By  Charles  E. 

Keyes, XXX.  323 

The  Clealum  Iron-Ores,  Washington.  By  George  Otis  Smith 

and  Bailey  Willis, XXX.  356 

The  Cripple  Creek  Volcano.     By  T.  A.  Eickard,        .        .        .  XXX.     367 

Geological  Eelations  of  the  Iron-Ores  in  the  Cartersville  Dis- 
trict, Georgia.  By  C.  Willard  Hayes,  .  ,  .  .  .  XXX.  403 


SOME    PRINCIPLES    CONTROLLING   DEPOSITION    OF    ORES.       789 

TITLE.  VOL.  PAGE 
The  Enrichment  of  Gold-  and  Silver- Veins.  By  Walter  Har- 
vey Weed, XXX.  424 

Types  of  Copper-Deposits  in  the  Southern  United-States.  By 

Walter  Harvey  Weed, .  XXX.  449 

The  Oil -Bearing  Shales  of  the  Coast  of  Brazil.  By  Prof.  John 

C.  Branner, XXX.  537 

Metasomatic  Processes  in  Fissure-Veins.  By  Waldemar  Lind- 

gren, XXX.  578 

Notes  on  the  Occurrence  of  Platinum  in  North  America.  By 

David  T.  Day, XXX.  702 

The  Telluride-Ores  of  Cripple  Creek  and  Kalgoorlie.  By  T.  A. 

Rickard, XXX.  708 

An  Occurrence  of  Limburgite  in  the  Cripple  Creek  District. 

By  E.  A.  Stevens, XXX.  759 

The  Iron-Mines  of-  Hartville,  Wyoming.  By  H.  M.  Chance,  .  XXX.  987 
The  Indicator  Vein,  Ballarat,  Australia,  By  T.  A.  Eickard,  .  XXX.  1004 

The  Geology  and  Vein-Phenomena  of  Arizona.  By  Prof. 

Theodore  B.  Comstock,          .        .        .  XXX.  1038 


INDEX. 


NOTE.— The  names  of  actual  contributors  to  this  volume  are  set  in  small  capitals, 
preceding  the  references  to  their  contributions.  References  to  citations,  whether  of 
actual  contributors  or  others,  are  preceded  by  the  names  of  the  authors  cited  in  lower- 
case type.  For  mere  allusions,  not  giving  further  details,  the  page-references  are 
printed  in  brackets. 


ADAKS,  F.  D. :  remarks  on  Lindgren,  634. 

Aguilera,  J.  and  Ordonez,  E.,  on  mineral  veins  of  Pachuca,  Mexico,  570. 

Alford,  C.  A.,  on  geology  of  the  Transvaal,  162. 

Alte  Hoffnung  Erbstollen  silver-mine,  Miteveida,  Saxony,  character  of  ground-water 
at,  29. 

Alterations:  country-rock,  660;  metasomatic,  classified,  660;  of  rocks  forming 
greisen,  mica-rock,  cassiterite-rock,  etc.,  660  et  seq.,  668. 

Altered  rocks  from  fold-quartz  veins,  analyses  of,  587. 

Aluminum,  proportions  of,  in  the  earth's  crust,  639. 

Alum-stone,  formation  of,  661,  669. 

Ammerberg,  Sweden,  character  of  zinc-blende  deposits  at,  141  et  ssq. 

Amphibole  in  Bunker  Hill  and  Sullivan  lead-silver  mine,  Idaho,  530;  in  copper-veins 
of  Rossland,  British  Columbia,  530. 

Analyses:  altered  rocks  from  gold-quartz  veins,  587;  brick,  altered,  609;  Caliche, 
712;  Clausthal  (Germany)  rocks,  603;  Comstock  clays,  568;  country-rock  near 
Himmelfahrt  mine,  Freiberg,  Saxony,  529;  filling  of  fissure-veins,  37;  fresh  and 
altered  rocks  from  gold-quartz  veins,  589;  gas  liberated  from  warm  mineral 
water,  33 ;  gneiss  near  Himmelfahrt  mine,  Freiberg,  Saxony,  581,  582 ;  labra- 
dorite,  etc.,  662;  metasomatic  rocks  from  gold-quartz  veins,  586;  mineral 
waters,  42;  opaline  silica,  575;  propylitic  andesite,  566 ;  tin-deposits  of  Alten- 
berg  and  Zinnwald,  Saxony,  542;  waters  encountered  in  mines,  42;  well-waters, 
Tucson,  Ariz.,  714  ;  silicified  diorite,  593. 

Andreasberg,  Hartz  mountains,  silver-ore  veins  of,  81. 

Anthou,  E.  F.,  investigations  in  sulphide  reactions,  467. 

Apatite- veins  of  Canada,  635;  in  Norway  and  Sweden,  646. 

Argon,  proportions  of,  in  the  earth's  crust,  639. 

Arizona:  copper-deposits,  110,  131;  Bisbee,  447;  Clifton-Morenci,  447;  Globe,  447: 
copper-mines :  United  Verde,  447;  Hillside  mine,  mineral  veins  of,  213. 

Arrhenius,  Svante,  on  the  physics  of  vulcanism,  638 ;  on  chemical  and  physical  action 
of  water  upon  magma,  643,  644. 

Arsenic,  proportions  of,  in  the  earth's  crust,  639 ;  in  mineral  waters,  47. 

Ascending  waters :  carbonic  acid  the  most  important  geological  factor,  44 ;  encoun- 
tered in  mines,  28;  heat  of,  31  et  seq.  ;  hydrogen  sulphide  in,  44. 

Association  of  copper  and  iron  compounds,  364;  of  lead,  zinc  and  iron  compounds, 
357 ;  of  silver  and  gold  with  base  metals,  368. 

Australasia,  gold-deposits  of,  161,  221  et  seq. 

Australia;  copper  mines:  New  South  Wales;  Broken  Hill  Consols,  460,  461. 

Australian  Broken  Hill  Consols  silver-mine,  New  South  Wales,  490. 

BAIN,  H.  FOSTER  :  remarks  on  Van  Hise,  622 ;  on  Emmons  and  Weed,  627. 
Banat ;  mines  of,  718. 

(  791  ) 


792  INDEX. 

"  Banded  structure"  and  " crustification,"  204,  240,  260. 

Bauxites,  formation  of,  661. 

Barium,  proportions  of,  in  the  earth's  crust,  639. 

Barus,  C.,  on  the  action  of  hot  water  on  soft  glass  [643],  308. 

Barysphere:  does  it  exist  within  reach  of  circulating  waters?  271;  the  source  at 

unknown  depths  of  ore-deposits,  11,  73,  79,  200,  242,  264,  271. 
Beaumont,  Elie  de,  theory  of  "pentagonal  symmetry,"  8. 
BECK,  PKOF.  E.,  on  depth  of  ore-deposits,  671 ;  on  the  tin-ore  deposits  from  Banca 

and  Billiton,  543 ;  on  the  tin-ores  of  Etta  Knob,  Black  Hills,  S.  Dak.,  643  (foot- 
note) ;  Remarks  on  Van  Hise,  613 ;  on   Emnious  and  Weed,  615 ;  on  Lindgren, 

616. 

BECKER,  G.  F. :  remarks  in  discussion  of  the  genesis  of  ore-deposits,  204. 
Becker,  G.  F. :  analysis  of  filling  of  fissure-veins,  37 ;   on  the  Apollo  mine,  Unga 

Island,  Alaska,  572;  on  the  country-rock  of  the  Tread  well  mine,  Alaska,  593; 

on  the  geology  of  the  Comstock  lode,  566  ;  on  the  quicksilver-deposits  of  the 

Pacific  Coast,  595 ;  on  underground  temperature,  31. 
Belcher  silver-mine,  Storey  county,  Nev.,  location  of  bonanza,  93. 
Bell,  E.,  on  ore-deposits  of  Sudbury,  Canada,  146. 
Beryllium,  proportions  of,  in  the  earth's  crust,  639. 

Bescheert  Gliick  silver-mine,  Freiberg,  Saxony,  character  of  deposit,  78. 
Big  Seven  silver-lead  mine,  Neihart,  Mont.,  484.  • 
Biotite  replacing  hornblende  and  feldspars,  in  tourmaline  veins,  Meadow  Lake,  Cal., 

530 ;  in  gold-copper  veins  of  Eossland,  British  Columbia,  530. 
Biotite  replacing  quartz  in  Bunker  Hill  and  Sullivan  mine,  Idaho,  530;  secondary, 

in  Ocean  Wave  mine,  Cripple  Creek,  Colo.,  530. 
Bisbee  copper-deposits,  Cochise  county,  Ariz.  [446]. 
Bischof,  G. :  arsenic  in  mineral  waters  found  by,  47 ;  on  kaolinization  [661] ;  oil 

metallic  deposits  from  sea-water,  121. 

Black  Hills  of  Dakota:  observations  in,  in  connection  with  contact-deposits,  731. 
Black  Jack  copper-silver  mines,  Florida  Mountain,  Idaho,  573. 
BLAKE,  W.  P. :  remarks  in  discussion  of  the  genesis  of  ore-deposits,  188. 
Blake's  account  of  ore-deposits  in  Copper  Basin,  Ariz.,  132. 
Blue  Wing  copper-mine,  Virgilina  district,  Va.  and  N.  C.,  454. 
Blue  Wing  iron-mine,  Person  county,  N.  C.  [483]. 
Blum  on  pseudomorphs,  501. 

Bobierre,  A.,  amount  of  salt  in  rain-water  found  by,  43. 
Bohemia:  ancient  gold-workings  in   Trautenau  region,  163;  copper-sandstones  of, 

126 ;  kupferschiefer  of,  124 ;  ore-deposits  at  Przibram,  56,  61,  76,  83,  239  et  seq.  ; 

temperature  of  thermal  springs,  40;  tin-placers  at  Flatten,  159. 
Bohneisenerz  deposits,  136. 

Bonanzas  at  Andreasberg,  Germany  [679] ;  at  Kongsberg,  Norway  [679] ;  at  Schem- 
•  nitz,  Hungary  [679] ;  formation  of,  in  the  upper  portions  of  gold-veins,  734  et 

seq.;  in  Transylvanian  gold-veins  [679]. 
Boron,  proportions  of,  in  the  earth's  crust,  639. 
Botesiu  gold-field,  Dacian  district,  Transylvania,  89. 
Brick,  altered,  analysis  of,  609. 

Brogger,  W.  C.,  on  genesis  of  pegmatite-veins,  732 ;  on  pegmatite- veins  in  Norway,  647. 
Broken  Hill  Consols  silver-mine,  New  South  Wales,  Australia,  460,  461. 
Bromine,  proportions  of,  in  the  earth's  crust,  639. 
Brown,  E.  G.,  on  the  Butte,  Mont.,  copper-deposits,  384. 
Buena  Vista  gold-mine,  Cripple  Creek  district,  Colo.,  290. 
Bunker  Hill  and  Sullivan  silver-lead  mine,  Coeur  d'Alene  district,  Idaho,  601. 

Calamine-deposits  at  Raibl,  Carinthia,  134. 
Calcium,  proportions  of,  in  the  earth's  crust,  639. 


INDEX.  793 

Caledonia  gold-mine,  Thames  district,  New  Zealand,  richness  of  ore,  222. 

Caliche  of  Southern  Arizona  :  An  Example  of  Deposition  by  the  Vadose  Circulation  (BLAKE) 
710. 

California,  character  of  copper-ores  in  peninsula  of  Lower,  132;  silver-mine,  Storey 
county,  Nev.,  location  of  bonanza,  92. 

Canada,  apatite-deposits  of,  635 ;  ore-deposits  of  Sudbury,  145,  210 ;  platinum-metals 
at  Sudbury,  640. 

Canada  Hill  vein,  Grass  Valley,  Cal.,  342. 

Carbon,  proportions  of,  in  the  earth's  crust,  639. 

Carbonatization  of  rocks  (with  dolomitization,  etc,),  661  et  seq.,  668. 

Carbonic  acid  an  important  geological  factor  in  ascending  waters,  44. 

Carinthia:  analogy  of  Bleiberg  ore-deposits  with  those  of  Eureka  district,  Nev.,  112; 
calamine-deposits  of  Raibl,  134  ;  ore-deposits  at  Raibl,  61, 69,  102. 

Carlsbad  Sprudel :  analysis  and  temperature  of  water,  40,  42 ;  character  of  deposit,  53. 

Carniola,  Bohneisenerz  at  Wocheiu,  137. 

Cassiterite:  synthetic  production  of,  by  sublimation  [637];  and  iron-ore,  occurrence 
of  in  limestone  near  Campiglia,  Italy  [651] ;  cassiterite-veius,  614 ;  in  Banca  and 
Billitou  [645] ;  in  Cornwall,  England  [645] ;  in  Tasmania  [645]. 

Cause  of  flowage  of  underground  water,  302. 

Cavities  in  rocks,  character  of  filling,  15. 

CAZIN,  F.  M.  F. :  remarks  in  discussion  of  the  genesis  of  ore-deposits,  206,  269;  on 
copper-ores  of  New  Mexico,  131. 

Cephalonia,  water-power  of  the  sea-mills  of,  304. 

Cerium,  proportions  of,  in  the  earth's  crust,  639. 

Chamberliu,  T.  C.,  on  ore-deposits  of  Southwestern  Wisconsin  [301] ;  opinion  on  cause 
of  contact-metamorphism,  727. 

Chemical  constitution  of  mineral/ waters,  40. 

Chlorine,  proportions  of,  in  the  earth's  crust,  639. 

Chlorite  in  gold-quartz  of  Crown  Point  mine,  Grass  Valley,  Cal.,  530. 

CHURCH,  JOHN  A. :  remarks  in  discussion  of  the  genesis  of  ore-deposits,  195. 

Church's  account  of  the  Justice  silver-mine.  239  ;  views  on  source  of  underground 
waters,  31. 

Churprinz  silver-mine,  Freiberg,  Saxony,  ascending  mineral  waters  at,  29. 

Cinnabar-deposits  of  Sulphur  Bank,  Cal.,  32  et  seq.,  66. 

Circulating  waters  of  surface-origin,  435. 

Clarke,  F.  W.  and  Hillebrand,  W.  F.,  on  the  occurrence  of  elementary  substances  in 
the  earth's  crnst  [639]. 

Classification  of  fissure- veins  according  to  metasomatic  processes,  540  et  seq. ;  of  ore- 
deposits,  427;  proposed  modification  of,  211  et  seq.,  226;  systems  employed  hith- 
erto, 3. 

Clausthal  (Germany)  rocks,  analyses  of,  603;  Hartz  mountains,  ore-deposits,  79. 

Clays  of  Comstock  lode,  analysis  of,  568. 

Clifford  amalgamated  copper-mine,  Cornwall,  62. 

Clifton-Morenci  copper-deposits,  Graham  county,  Ariz.,  447. 

Cobalt,  proportions  of,  in  the  earth's  crust,  639. 

Cohen,  E.,  on  Witwatersrand  gold-deposits,  South  Africa,  162. 

COLLINS,  ARTHUR  L. :  remarks  on  Emmons  and  Weed,  620;  discussion  by  Emmons, 
756  et  seq. 

Colorado  :  gold-  and  silver-mines,  290,  342,  396. 

Colorado  :  L-ad-zinc  mines  :  Aspen  district :  Mollie  Gibson,  492  ;  Smuggler,  492;  ore- 
deposits  of  Leadville,  106;  Red  Mountain  district,  Ouray  county,  character  of 
ore-deposits,  109:  silver-lead-mines  [351] :  sil wr-mines  :  Custer  county ;  Geyser, 
461;  Mollie  Gibson,  450;  Pandora,  451;  Smuggler-Union,  451;  Smuggler,  450; 
Yankee  Girl,  451. 

Comstock  Lode,  Storey  county,  Nev.  :  geological  conditions  of,  90;  heat  of  ascending 
waters  at,  31;  ore-deposition  of,  195,  239. 


794  INDEX. 

Concentration  by  reaction  upon  sulphides  compared  with  metallurgical  concentra- 
tion, 376. 

Concentration  of  ores:  special  factors  affecting,  393;  character  of  the  topography, 
416 ;  character  of  the  topography — effect  of  the  vertical  element,  416  ;  character 
of  the  topography — effect  of  the  horizontal  element,  417;  physical  revolutions, 
419;  variations  in  porosity  and  structure,  393;  variations  in  porosity,  etc., — com- 
plexity of  openings,  394;  variations  in  porosity,  etc., — impervious  strata  at  vari- 
ous depths,  396;  variations  in  porosity,  etc., — pitching  troughs  and  arches,  405 
variations  in  porosity,  etc., — pre-existing  channels  and  replacements,  413. 

Condition  of  water  in  the  zone  of  fracture,  291. 

Conical  mounds  built  by  ascending  mineral  waters,  39. 

Consolidated  Virginia  silver-mine,  Storey  county,  Nev.,  location  of  bonanza,  92. 

Contact-Deposits:  Constituent  Minerals,  717 ;  Form,  717 ;  Genetic  classification :  " con- 
tact metamorphic  "  deposits,  730 ;  Dynamo-metamorphic  and  regional-metamor- 
phic  deposits,  731;  hydrothermal  deposits,  730;  Geographic  Distribution  :  Arizona, 
723;  British  Columbia,  723;  California,  720;  Idaho,  721,  722  et  seq. ;  Mexico,  724, 
725 ;  Northwest  Territory,  723  et  seq. ;  Other  Countries,  725 :  Literature :  718  et  seq. ; 
Origin  of  the  Deposits,  725,  726;  Position,  717. 

Contact-metamorphism :  691,  726,  727 ;  Cause  of  Contact-Metamorphism,  727,  728, 729; 
intense,  of  rocks,  661  et  seq.,  669;  ore-deposits  formed  by,  648. 

Copper-deposits:  Arizona:  Cochise  county;  Bisbee,  447;  Gila  county;  Globe,  447; 
Graham  county :  Clifton-Morenci,  447. 

Copper-mines:  Arizona:  Cochise  county;  Copper  Queen  [446]  ;  Yavapai  county; 
United  Verde,  447;  Colorado:  Boulder  county;  Orphan  Boy,  738;  New  Mexico: 
Grant  county  ;  Santa  Eita,  449  ;  Grant  county ;  Hanover,  450  ;  North  Carolina  : 
Eowan  county ;  Union  Copper  Company's,  454  ;  North  Carolina  anil  Virginia :  Vir- 
giliua  district;  Blue  Wing,  454. 

Copper-ore  deposits  in  Butte,  Mont.  [657] ;  in  Cornwall,  England  [657]. 

Copper-ores:  Arizona,  110,  131;  Bohemia,  124,  126;  Lake  Superior  district,  144; 
Lower  California,  132;  Mannsfeld,  124;  Mexico :  Chihuahua,  458;  New  Mexico, 
110,  131,  210;  Prettau,  Tyrol,  143;  St.  Avoid,  127;  Sweden,  140;  SOUTH 
AMERICA:  Peru:  Cerro  de  Pasco  mining  district,  458:  Vermont,  207;  West- 
phalia, 125. 

Copper  Queen  copper-mine,  Bisbee,  Cochise  county,  Ariz.  [446]. 

Copper-silver  mines:  Idaho:  Florida  Mountain  ;  Black  Jack,  573  ;  Trade  Dollar,  573. 

Copper-sandstone  of  Bohemia,  126. 

Cordilleran  region  of  the  Western  U.  S.,  304. 

Cornwall  (England)  copper  veins  of,  620;  tin-deposits  of,  139. 

Coronado  copper-mines,  449. 

Cotta,  B.  von  :  classification  of  ore-deposits  by,  4 ;  on  ore-deposition,  124  et  seq. ;  mines 
of  the  Banat,  in  Austria,  718. 

Cotta,  B.  von  and  Swess,  Edward,  on  the  iron-ore  deposits  in  the  Banat.  Hungary 
[648]  (footnote). 

Country-rock  near  Himmelfahrt  mine,  Freiberg,  Saxony,  analysis,  by  Dr.  H.  Schulze, 
529. 

Critical  temperatures  of  water,  etc.,  659. 

Crosby,  W.  F.  and  W.  O.,  on  the  sea-mills  of  Cephalonia,  304. 

Cross,  Whitman,  and  Penrose,  E.  A.  F.,  on  mineral  deposits  of  the  Cripple  Creek  dis- 
trict, Colo.,  574. 

"  Gratification,"  12,  198,  204.  240,  260,  277. 

Crystalline  schists,  ore-deposits  in,  137. 

Cumberland,  England,  iron-ore  deposits,  136. 

Dacian  gold-fields,  Transylvania,  86,  97. 

Daintree,  experiment  on  crystallization  of  gold,  743. 


INDEX.  795 

Dakota,  gold-deposits  of  Black  Hills,  160. 

Dalmer,  K.,  on  "  bed-impregnations  "  at  Schwarzenberg,  650. 

Daubree,  Prof.  A. :  on  alterations  produced  by  mineral  springs,  48  et  seq.;  on  causes 

of  strise  in  lode-walls,  213;  on  the  kaolin-deposits  of  Cornwall,  France  and  Ger- 
many, 661;  on  subterranean  water-circulation,  18  et  seq. 
DE  LAUNAY,  PROF.  L.  C. :  remarks  on  Emmons  and  Weed,  616,   . 
De  Launay  on   chemical  theory  of  ore-deposits,   8,  63 ;  on  metalliferous  deposits, 

[476],  389,  455,  672  ;  views  on  "  secondary  enrichment,"  758;  on  the  relation  of 

secondary  reactions  to  the  ground  water-level,  759. 
Deposition  by  vadose  circulation,   Caliche  of  Southern  Arizona  an  example  of,  710 

et  seq. 
Deposition  of  ores,  some  principles  controlling  the,  282;  of  oxides  below  water-level, 

438  ;  of  sulphides,  438. 
Detrital  deposits,  152. 

Devereux,  W.  B.,  on  occurrence  of  gold  in  Black  Hills,  Dak.,  160. 
Devon  Consols  copper-mine,  Cornwall,  621. 
Disci ssion,  spaces  of,  13,  74. 
Dissolution,  spaces  of,  13, 95. 

Distribution  of  elementary  substances  in  the  earth's  crust,  639. 
Doelter,  Dr.  C.,  synthetic  experiments  in  sulphide  reactions,  469. 
Dolcoath  gold-mine,  near  Elkhorn,  Mont.  [496]. 
Douglas,  James,  on  the  Butte,  Mont.,  copper-deposits,  383 ;  on  the  Copper  Queen  mine, 

Bisbee,  Ariz.  [446]. 

Ducktown,  Tenn.,  copper-deposits,  383,  715. 
Dux  coal-mine  (lignite),  Bohemia,  irruption  of  thermal  waters  at,  30. 

East  Wheal  Lovell  tin-mine,  Cornwall,  Eng.,  character  of  ore-body,  139. 

Einigkeit  silver-mine,  Joachimsthal,  Saxony,  ascending  mineral  springs  at,  30. 

Elba:  iron -ore  deposits  [648]. 

Emmons,  S.  H.,  on  decomposition  of  metals,  149. 

EMMONS,  S.  F. :  The  Secondary  Enrichment  of  Ore-Deposits,  433 ;  remarks  in  discussion 
of  Collins,  Vogt,  De  Launay,  etc.,  756  et  seq.;  of  Lindgren  on  "Contact-Depos- 
its," 759  ;  of  Posepny,  199. 

Emmons,  S.  F.,  on  the  Butte,  Mont.,  copper-deposits,  384  ;  on  descending  waters,  107; 
on  the  fissure-vein  of  Queen  of  the  West  lead-silver  mine,  Ten  Mile  district, 
Colo.,  597 ;  on  the  Leadville,  Colo.,  silver-deposits,  388 ;  on  the  mines  of  Custer 
co"unty,  Colo.,  351. 

Emmons,  S.  F.,  and  Whitman  Cross,  on  propylitic  deposits  of  Silver  Cliff  and  Rosita 
Hills,  Colo.,  572. 

Emmous,  S.  F.,  W.  H.  Weed  and  Tower,  on  copper-veins  of  Butte,  Mont.,  596. 

England  :  iron-ores  of  Cumberland,  136;  lead-mining  in  north  of,  104. 

Enrichment  of  Gold-  and  Silver- Veins  (WEED),  473. 

Enrichment  of  gold-veins  near  the  surface:  by  concentration,  736;  by  descending 
waters,  737;  by  precipitants,  742 ;  by  solution,  739;  by  solution  and  precipita- 
tion, 744. 

Enterprise  gold-  and  silver-mine,  Rico,  Dolores  county,  Colo.,  290,  342,  396. 

Epigenetic  deposits,  differences  of  depth  in  the  original  positions  of,  and  secondary 
alteration  of  deposits,  669,  671. 

Erbsenstein,  deposits  of,  at  Carlsbad,  53. 

Eruptions,  sequence  of,  689. 

Eruptive  after-actions,  ore-deposits  formed  by,  643;  cassiterite-veins  and  apatite- 
veins,  645,  646;  pegmatite-veins,  647. 

Eruptive  processes,  relation  of,  to  the  formation  of  ore-deposits,  641. 

Eruptive  rocks:  deposits  in,  137  ;  influence  on  ore-deposition,  191 ;  relation  of  thermal 
springs  to,  221. 


796  INDEX. 

Erzgebirge,  mineral  springs  in  mines  of,  30 ;  ore-deposits,  82;  veins  of  the,  614,615. 
Etta  Knob,  643  (footnote);  tin-ore  deposits,  Black  Hills,  S.  Dak.,  643  (footnote). 
Eureka  district,  Nev.,  geological  conditions  of,  112. 
Eva  May  silver-lead  mine,  Boulder  county,  Mont.,  495 ;  analysis  of  ore,  495. 

Factors  influencing,  depth  at  which  rock-flowage  occurs,  287. 

Faribault,  E.  R.,  on  the  gold  measures  of  Nova  Scotia,  412. 

Filons  stanniferes,  665. 

Filons  sulfures  dites  plombiferes,  665. 

Fissures :  filling,  analysis  of,  37 ;  of  dislocation,  14 ;  ore-deposits  in,  74 ;  theories  of 

origin  of,  212. 

Fissure-veins,  metasomatic  processes  in,  498  et  seq. 
Florence  silver-lead  mine,  Neihart,  Mont.,  484. 
Flowage:    factors   influencing   depth   of  occurrence,   287;    of  underground   water, 

cause  of,  302 ;    of  water  in  capillary  openings,  Poiseuille's  law,  297 ;    zone  of, 

286. 

Flow  of  rocks,  experiments  in,  by  F.  D.  Adams,  McGill  University  [287]. 
Fluorine,  proportions  of,  in  the  earth's  crust,  639. 
Fluorite  in  Independence  mine,  Cripple  Creek,  Colo.,  524. 
Forchhammer  on  kaolinization  [661]. 

Formation  of  Bonanzas  in  the  Upper  Portions  of  Gold- Veins  (RICKARD),  734. 
Foster,  C.  Le  Neve,  on  tin-deposits  of  Cornwall,  139. 
Foullon,  A.  B.  von,  on  ore-deposits  of  Sudbury,  Canada,  145,  146. 
Fowry  Consols  copper-mine,  Cornwall,  620. 
Fracture :  condition  of  water  in  zone  of,  291 ;  division  of  zone  of,  into  a  belt  of 

weathering  and  a  belt  of  cementation,  327;  ore-deposits  derived  from  zone  of, 

300 ;  zone  of,  286;  zone  of,  material  for  ore-deposits  derived  from  rocks  in,  302. 
Fracture  and  flowage,  zone  of  combined,  288. 

France  :  Fontainebleau  sandstone,  119;  iron-ore  deposits  of  Dielette  [648]. 
Freiberg,  Saxony,  ore-deposits,  78,  615,  616. 
Freiberg,  Bavarian  Upper  Palatinate,  lead-deposits,  129. 
Fresh  and  altered  rocks  from  gold-quartz  veins,  analysis  of,  589. 
Frohner  silver-lead  mine,  near  Helena,  Mont.,  496  ;  analysis  of  ore,  496. 
Fuchs,  E.,  on  copper-ores  of  lower  California,  132. 
Furman,  H.  van  F.,  on  mines  near  Mapimi,  Durango,  Mex.  [445]. 

Gage,  J.  E.,  on  occurrence  of  lead-  and  zinc-ores  in  Missouri,  115. 

Galena:  replacing  calcite  in  Elkhorn  mine,  Mont.,  537;  tree-stems  changed  to,  at 

Vesuvius  lead-mines,  Bavaria,  129. 

Garnet  in  gold-quartz  veins  of  Broken  Hill,  New  South  Wales,  531. 
Gas,  analysis  of,  liberated  from  warm  mineral  water,  35. 
Geodes,  opal  and  chalcedony,  mineral  deposits  in,  24. 
Germany  :  copper  ores,  124  et  seq. ;  lead-deposits  of  Mecheruich,  near  Commern,  127; 

iron-ore  deposits  of  Alsace,  136 ;  tin-placers  at  Annaberg,  Saxony,  159. 
Geyser  silver-mine,  Silver  Cliff,  Custer  County,  Colo.,  461. 
Gilbert,  G.  K.,  on  the  Cordilleran  region  of  the  Western  U.  S.,  304. 
Globe  copper-deposits,  Gila  county,  Ariz.,  447. 

Gneiss  near  Himmelfahrt  mine,  Freiberg,  Saxony,  analysis  of,  581,  582. 
Gold:  ancient  placer-mining  in  Bohemia,  163;  occurrence  of,   in  Gympie  district, 

Queensland,  744;  in  manganese  spar,  67;  at  Rico,  Colo.,  744. 
Gold  Hill  silver-mine,  Storey  county,  Nev.,  high  temperature  of  water  in,  31. 
Gold  in  pyrite  of  Orphan  Boy  copper-mine,  Boulder  county,  Colo.,  738. 
Gold-mines:  Arizona:  Final  county;  Mammoth,  salt  in  water  of,  741;    California: 

Calaveras  county:    Rathgeb,   725,  749,   750;    Colorado:   Cripple    Creek;    Moon 

Anchor,  747,  748;  Cripple  Creek  district;  Buena  Vista,  290;  Lee,  290;  Smuggler, 


INDEX.  797 

290;  Victor,  290;  FOREIGN  COUNTRIES:  Australia:  Bright  district;  Myrtle, 
746,  747;  Bright  district;  Shouldn't  Wonder,  746;  Western  Australia :  Kalgoorlie; 
Great  Boulder  Main  Reef,  742:  Kalgoorlie;  Great  Boulder  Proprietary,  salt  in 
water  of,  740;  Kunanalling;  Sugar  Loaf,  742;  New  Zealand:  Thames  district: 
Moanataeri,  752;  Montana:  Elkhorn ;  Dolcoath  [496];  Elkhorn;  Mayflower 
[496].  (NOTE.  The  numerous  passing  references  to  gold-mines,  occurring  in 
Prof.  Posepuy's  paper,  have  not  been  separately  indexed.) 

Gold-ores:  deposits  of  Black  Hills,  S.  Dak.,  160;  Beresov,  Ural  Mountains,  76;  Hun- 
gary, 85 ;  of  Australasia,  161,  221  et  seq.  ;  in  the  Ural  mountains,  76,  153 ;  New 
Zealand :  Hauraki  or  Thames  gold-field,  221 ;  Otago  gold-field,  224 ;  South  Africa: 
Witwatersrand,  162 ;  Sweden;  Falun,  141;  Transylvania,  Dacian  gold-field,  86; 
Verespatak,  Transylvania,  66,  87. 

Gold-  and  silver-mines  :  Colorado :  Dolores  county ;  Enterprise.  2!)0.  342,  396.  Nevada: 
see  Comstock  Lode. 

Gold  and  silver  in  eruptive  magmas,  641. 

Gold  and  silver  veins,  enrichment  of,  473  et  seq, 

Gold  quartz  veins,  614. 

Gold-veins:  enrichment  of,  near  the  surface  by  concentration,  736 ;  by  descending 
waters,  737,  738;  by  solution,  739;  by  solution  and  precipitation,  744;  formation 
of  bonanzas  in  the  upper  portions  of,  et  seq.,  734. 

Gottes  Geschick  silver-mine,  Swarzenberg,  Saxony,  ascending  waters  at,  29. 

Great  Boulder  Main  Reef  gold-mine,  Kalgoorlie,  W.  Australia,  742  ;  salt  in  water  of, 
740. 

Great  Extended  Hustlers  gold-mine,  Victoria,  Australia,  character  of  quartz  at,  215. 

Greece,  ore-deposits  of  Laurium,  135,  246. 

Grimm,  J. :  classification  of  ore-deposits  by,  4  ;  examination  of  Transylvania  ore-de- 
posits by,  96. 

Groddeck,  A.  v. :  mines  of  Banat,  718 ;  on  ore-deposition,  122  et  seq. ;  on  the  vein-sys- 
tem of  Clausthal,  Germany,  602;  system  of  classification  of  ore-deposits,  4. 

Groundwater,  695 ;  artesian  basins,  701 ;  common  conception  of,  695  ;  experience  in 
deep  mines  and  wells,  696  ;  hot-springs,  702 ;  irregular  distribution  of,  near  the 
surface,  705  ;  level,  436;  movements  of,  19. 

Guiterman,  F.,  on  the  gold-deposits  of  Battle  Mountain,  Colo,,  740. 

Gypsum  :  origin  of  some  beds,  715. 

Hale  and  Norcross  silver-mine,  Comstock  Lode,  Nev.,  flooding  of,  by  water,  31. 

Hanover  copper-mines,  Grant  county,  N.  M.,  450. 

Hartz  mountains,  ore-deposits,  79. 

Hauraki  or  Thames  gold-field,  New  Zealand,  221. 

Helena  and  Frisco  silver-lead  mine,  Coeur  d'Alene  district,  Idaho,  600. 

Helmhacker,  R.,  on  ore-deposits  of  Altai  region,  Siberia,  155. 

Highland  Boy  copper-mine,  450. 

Hills,  R.  C.,  on  the  ore-deposits  of  Summit  district,  Rio  Grande  county,  Colo.,  584. 

Hillside  gold-  and  silver-mine,  Ariz.,  mineral  veins  of,  213. 

Hintze,  C.,  on  kaolin  [664]. 

Holroyd's  (A.  G.),  collection  of  specimens  from  gold-district  of  West  Australia,  677 

et  seq. 

Hot  mineral  waters  encountered  in  mines,  31. 
Hungary :  geode  of  iron  opal  from  Dreiwasser,  24 ;  iron-ore  deposits :  in  the  Banat 

[648] ;  iron-ore  deposits :  Vasko  [648] :  ore-deposits  of,  85  et  seq. :  silver-deposits  of 

Rezbanya,  99. 
Hunt,  T.  Sterry,  on  the  copper-deposits  at  Ore-Knob,  N.  C.,  and  in  Carroll  county, 

Va.,  454 ;  on  pseudomorphs,  502. 
Hussak,  E.,  on  auriferous  pyritic  quartz-bed-vein  at  Passagem,  Brazil  [657] ;  on  the 

auriferous  quartz-vein  of  Passagem,  Minas  Geraes,  Brazil,  546. 


798  INDEX. 

Hutton,  F.  W.,  011  the  auriferous  veins  of  Hauraki  gold-fields,  Thames  district,  New 

Zealand,  571. 
Hydrogen,  proportions  of,  in  the  earth's  crust,  639;    sulphide,  important  part  of,  in 

ascending  waters,  44. 
Hysterogenites.  16,  17. 
Hysteromorphous  ore-deposits,  147. 

Idiogenous  mineral  deposits,  10. 

Igneous  rocks:  competence  of,  to  supply  vein-material,  682;  role  of,  in  the  formation 
of  veins,  680. 

Illustrations  of  secondary  enrichment  and  diminution  of  richness  with  depth,  383. 

Independence  gold-mine,  Cripple  Creek,  Colo.,  salt  in  water  of,  741. 

Iodine,  proportions  of,  in  the  earth's  crust,  639. 

Iron,  proportions  of,  in  the  earth's  crust,  639. 

Iron-mines:  North  Carolina:  Person  county;  Blue  Wing  [483]. 

Iron  opal,  geode  of,  from  Dreiwasser,  Hungary,  24. 

Iron-ore :  deposits  at  Vasko,  Hungary  [648] ;  of  Dielette,  France  [648] ;  of  Kristi- 
ania  region,  Norway  [648],  649 ;  in  the  Banat,  Hungary  [648] ;  in  the  island  of 
Elba  [648] ;  increase  of,  in  depth  in  manganese-deposits,  675. 

Iron-ores  :  analogy  of  Bohemian  and  Michigan,  237 ;  deposition  of,  in  Mesabi  range, 
Minn. ,229;  England,  Cumberland,  136;  Germany,  Alsace,  136;  Lake  Superior 
deposits,  228;  Norway,  138;  Spain,  Eio  Tinto  (limonite),  148;  Sweden,  Taberg 
(magnetite),  138;  Switzerland,  Carniola,  136;  Tyrol,  143. 

Irving,  Prof.  E.  D.,  on  the  copper-bearing  rocks  of  Lake  Superior,  607. 

Jacquet,  Mr.,  on  secondary  sulphides  at  Broken  Hill  lode,  N.  So.  Wales,  Austra- 
lia, 459. 

Jenney,  W.  P.,  on  the  lead-  and  zinc-deposits  of  the  Mississippi,  452. 
Joachimsthal  mines,  Bohemia,  mineral  waters  of,  30. 
Joplin  lead-  and  zinc-district,  Mo.,  623. 
Justice  silver-mine.  Storey  county,  Nev.,  character  of  ore-deposit,  92,  198,  239. 

Kackar  district,  southern  Ural,  Russia,  ore-deposits  of,  157. 

Kahlenberg,  L.,  and  Lincoln,  A.  T.,  on  solutions  of  silicates,  319. 

Kaolin-deposit  at  Ekersund-Soggendal,  Norway,  662. 

Kaolinite  in  vein  near  Boulder,  Mont.,  534 ;  in  propylitic  veins  at  Cripple  Creek, 
Colo.,  534;  in  veins  at  Delamar,  Idaho,  534;  in  veins  of  Summit  district,  Colo., 
534 ;  and  sericite  in  veins  of  the  pyritic  galena-formation  of  Freiberg,  Saxony, 
534. 

Kaolin ization  of  rocks,  660  et  seq,,  668. 

Katrontza  gold-mine,  Verespatak,  Transylvania,  character  of  ore  at,  66,  67. 

KEMP,  J.  F. :   The  Role  of  the  Igneous  Rocks  in  the  Formation  of  Veins,  680. 

Kendall,  J.  D.,  on  iron-ores  of  Cumberland,  Eng.,  136. 

Kerr,  W.  C.,  on  North  Carolina  gold-deposits,  153. 

Keweeuaw  Point,  Lake  Superior  region,  copper-bearing  rocks  of,  344. 

KEYES,  CHARLES  E. :  remarks  on  Van  Hise,  628;  on  Liudgren,  630. 

Kjerulf,  Th. :  on  the  iron-ore  deposits  of  the  Kristiania  region,  Norway  [648]  (foot- 
note; ;  on  iron-ore  deposits  in  Norway,  138. 

Kongsberg  silver-mines,  Norway,  468. 

Kupferschiefer  of  Mannsfeld,  Thuringia  and  Bohemia,  123,  124. 

Labradorite,  etc.,  analyses  of,  662. 

Lacroix,  A.,  on  axinitizatiou  of  contact-metamorphic  zones  in  the  Pyrenees  [650]. 

Lake  Superior  region:  copper-deposits,  144;  iron-ores  of,  227. 

Lanthanum,  proportions  of,  in  the  earth's  crust,  639. 


INDEX.  799 

Lapparent,  A.  de,  on  metamorphism,  118. 

Lateral-secretion  theory  of  ore-deposition,  57  etseq.,  190,  200,  236,  242,  254,257,  271. 

Laurium,  Greece,  ore-deposits,  135,  246. 

Leaching :  of  wall-rock,  277 ;  in  the  zone  of  weathering,  476  et  seq, 

Lead-ores:  Freihung,  Bavarian  Upper  Palatinate,  129;  Missouri  and  Wisconsin,  115; 
Mechernich,  near  Commern,  Germany,  127;  North  of  England,  105. 

Leadville,  Colo.,  ore-deposits,  106. 

Lead-silver  mines:  Colorado :  Ten  Mile  district ;  Queen  of  the  West,  597. 

Lead-zinc  mines:  Colorado  :  Aspen  district;  Mollie  Gibson,  492;   Smuggler,  492. 

LE  CONTE,  PROF.  JOSEPH  :  on  genesis  of  ore-deposits,  270 ;  on  mineral  vein-forma- 
tion, 33. 

Lee  gold-mine,  Cripple  Creek  district,  Colo.,  290. 

Lemberg's  experiment  in  the  solution  of  anhydrous  powdered  silicates  by  boiling 
water  [643]. 

Limestone,  silicified,  Diadem  lode,  Plumas  county,  Cal.,  521. 

LINDGREN,  WALDEMAR  :  Metasomatic  Processes  in  Fissure-  Veins,  498 ;  The  Character  and 
Genesis  of  Certain  Contact- Deposits,  716. 

Lindgren,  W.,  on  contact-deposits,  759;  on  fissure-veins  of  the  Trade  Dollar  and  Black 
Jack  mines,  Idaho,  573;  on  gold-belt  of  the  Sierra  Nevada,  290;  on  gold-quartz 
veins  of  California,  585;  on  granitic  and  dioritic  rocks  of  Meadow  Lake,  Nevada 
county,  Cal,,  562 ;  on  the  Sierra  Nevada,  342 ;  on  silver-lead  veins  of  Wood  River, 
Idaho,  599  ;  on  quartz-veins  of  De  Lamar,  Idaho,  583. 

Lithium,  proportions  of,  in  the  earth's  crust,  639. 

Lithosphere  ;  zone  of  flowage,  286  ;  zone  of  fracture,  286. 

Liversidge,  experiments  on  precipitation  of  gold  from  solution  by  metallic  sulphides, 
[482]. 

Lock,  A.  G.,  on  gold-deposits,  152. 

Lotti,  B.,  on  the  Elba  iron-ore  deposits  [648]  (footnote). 

Lottner,  classification  of  ore-deposits  by,  7. 

McKellar,  Peter,  on  quartz-veins  in  granite  at  Lake  of  the  Woods,  Western  Ontario, 
593. 

Magmatic  segregation,  etc. :  auriferous  pyrites  of  Rossland,  B.  C.,  642  ;  chromite  in 
peridotites  and  their  secondary  serpentines  [642] ;  copper-ores  (high-grade)  in 
serpentinized  peridotites  [642];  metallic  nickel-iron  in  eruptive  rocks  [642]; 
platinum-metals  in  highly  eruptive  rocks  [642] ;  nickeliferous  pyrrhotites  in 
gabbro  [642] ;  ore-deposits  formed  by,  642  ;  deposits  formed  by:  titanic  iron-ores 
in  basic  and  intermediate  eruptives  [642]. 

Magnesite  in  country-rock  near  Idaho  vein,  Grass  Valley,  Cal.,  526. 

Magnesium,  proportions  of,  in  the  earth's  crust,  639. 

Magnetite-deposit  at  Kirunawara-Luossawara,  Sweden,  676. 

Major  part  of  ore-depositing  water  is  meteoric,  302. 

Mammoth  gold-mine,  Pinal  county,  Ariz.,  salt  in  water  of,  741. 

Manganese,  proportions  of,  in  the  earth's  crust,  639. 

Manner  of  filling  open  spaces  in  general,  63. 

Mannsfeld  kupferschiefer,  123. 

Marine  detritus,  157. 

M£tyas  Kiraly  gold-mine,  Verespatak,  Transylvania,  character  of  native  gold  at, 
68,  70. 

Mayflower  gold-mine,  near  Elkhorn,  Mont.  [496]. 

Mesabi  range,  Minn.,  iron-ores  of,  229. 

Metals:  found  in  mineral  waters,  45  et  seq. ;  heavy,  original  source  of  the,  637;  pres- 
ence of  in  igneous  rocks,  682;  presence  of  in  sedimentary  and  metamorphic 
rocks,  684. 

Metamorphous  ore-deposits,  118  et  seq. 


800  INDEX. 

Metasomasis,  first  use  of  term,  6,  195. 

Metasoruatic  ore-deposits  iu  soluble  rocks,  133,  250. 

Metasomatic  Processes  in  Fissure-  Veins  (LlNDGREN),  498. 

Michel -Levy  on  the  French  iron -ore  deposits  [648]. 

Mine  La  Motte,  Madison  county,  Mo.,  lead-deposits  at,  117. 

Mineral  coatings  on  copper  at  the  Springs  of  Bourbon  1'Archambault,  France,  470. 

Mineral  deposits:  hysteromorphous,  147;  idiogenous  and  xenogenous,  10  et  seq. ;  in 

limestone  caves,  24;  in  geodes,  24;  metamorphous,  118. 
Mineral  springs:  at  the  surface,  37;  structural  features  of  deposits  by,  52.  . 
Mineral  waters :  alterations  produced  by,  48  ;  analyses  of,  37,  42  et  seq.  ;  arsenic  in,  47; 

chemical  constitution  of,  40;  minute  metallic  admixtures  in,  45;  temperature 

of,  40. 

Mining,  depth  of  [657]. 
Mining  districts,  distribution  of,  706. 
Missouri :  lead-regions  of,  115;  ore-deposits  of,  188. 

Moanataeri  gold-mine,  Thames  district,  New  Zealand,  752  ;  richness  of  ore,  222. 
Mollie  Gibson  lead-zinc  mine,  Aspen  district,  Colo.,  492. 
Mollie  Gibson  silver-mine,  Pitkin  county,  Colo.,  450. 
Montana:  gold-mines:  Elkhorn;  Dolcoath  [496];  Mayflower  [496]. 
Montana :  silver-lead  mines :  Eva  May,  495,  analysis  of  ore,  495;   Helena ;  Frohner, 

496,  analysis  of  ore,  496  ;  Neihart ;  Florence,  484  ;  Big  Seven,  484. 
Montana:  silver-mines:  Butte  district;  Euby  [482]. 
Moon  Anchor  gold-mine,  Cripple  Creek,  Colo.,  747. 
Miiller,  H.,  011  mineral  springs,  28. 
Myrtle  gold-mine,  Bright  district,  Australia,  747. 

Naumann  on  pseudomorphs,  501. 

Nevada:   character  of  ore-deposits,  110  et  seq.;   Comstock  Lode,  30,  89,   195,  239; 

Steamboat  Springs,  thermal  waters  of,  36  et  seq. 

Newberry,  Prof.  J.  S. :  on  classification  of  ore-deposits,  7 ;  origin  of  ores,  131. 
New  Mexico:  copper-deposits,  110,  131,  210;  copper-mines;  Hanover,  450;  Santa  Eita, 

449. 

New  Zealand  :  gold-fields  of,  221  et  seq. ;  gold  in  coal-measures  of,  161. 
Nickel,  proportions  of,  in  the  earth's  crust,  639. 
Nickel -pyrrhotite  deposit  at  Erteli,  Norway  [676]. 
Nitrogen,  proportions  of,  in  the  earth's  crust,  639. 

N5ggerath,  J.,  on  alterations  produced  by  mineral  waters,  49,  101,  201,  245. 
North  Carolina :  copper-mines ;  Union  Copper  Company's,  454 ;  iron-mines  :  Person 

county;  Blue  Wing  [483]. 

North  Iron  Hill,  Lake  county,  Colo.,  ore-deposits  of,  202  et  seq. 
North  Ophir  silver-mine,  Comstock  Lode,  Nev.,  high  temperature  of  water  in,  31. 
Norway:  iron-ore  deposits,  140 ;  Kristiania  region  [648],  649    kaolin-deposits:  Eker- 

sund-Soggendal,  662. 
Nuggets,  origin  of,  678  (footnote). 

Offenbanya  gold-mines,  Dacian  district,  Transylvania,  86,  87. 

Opaline  silica,  analysis  of,  575. 

Openings  :  in  rocks,  293;  size  and  number  of,  295. 

Ore-bonanzas,  distribution  of,  745. 

Ore-chutes,  421. 

Ores;  some  principles  controlling  the  deposition  of,  282. 

Ore-deposits:  at  Broken  Hill,  Australia  [679] ;  at  Chanarcillo,  Chile  [679];  chemical 
views  of  French  school,  8,  63;  classification  of,  427;  classification  hitherto  em- 
ployed, 3;  Comstock  Lode,  Storey  county,  Nev.,  195;  derived  from  zone  of  frac- 
ture, 300;  detrital,  154;  examples  of  classes  of,  72;  formed  by  chemical  and  me- 


INDEX.  801 

chanical  influences  of  surface  region,  148 ;  hysteromorphous,  147 ;  hysteromor- 
phous,  of  older  geological  formation,  160;  in  crystalline  schists  and  eruptive 
rocks,  79,  85,  137;  in  soluble  rocks,  95  ;  material  for,  derived  from  rocks  in  zone 
of  fracture,  302;  Mednorudjansk,  Ural  Mts.,  Kussia  [679];  metamorphous,  118; 
metasomatic,  in  soluble  rocks,  133;  origin  of,  in  deep  regions,  55;  Oruro,  Bolivia 
[679] ;  Pachuca,  Mexico  [679] ;  Pasco,  Peru  [679] ;  Potosi,  Bolivia  [679] ;  problems 
in  geology  of,  636  et  seq. ;  proposed  classification  of,  7,  211,  226 ;  secondary  enrich- 
ment of,  433  et  seq.;  the  result  of  work  of  underground  water,  285;  verchoviky, 
or  surface,  152;  Zacatecas,  Mexico  [679]. 

Ore-deposition;  in  fresh  water,  123;  influence  of  eruptive  rocks,  191;  John  Wood- 
ward's opinions,  two  hundred  years  ago,  192  ;  lateral  secretion  theory,  57  et  seq., 
190,  200,  236,  242,  254,  257,  271;  in  open  spaces,  64,  195,  239;  from  sea- water,  121. 

Ore-shoots,  localization  of,  746. 

Orphan  Boy  copper-mine,  Boulder  county,  Colo.,  738. 

Orthoclase  (valencianite) :  in  gold-silver  veins,  La  Valenciana,  Mexico,  532;  in  Valen- 
ciana  silver-mine,  Guanajuato,  Mexico,  532;  in  gold-silver  veins,  Silver  City, 
Idaho,  532. 

Otago  gold-field,  New  Zealand,  geological  formation  of,  224. 

Oxygen,  proportions  of,  in  the  earth's  crust,  639. 

Pandora  silver-mine,  San  Juan  county,  Colo..  451. 

Penrose,  A.  F.  B.,  on  enrichments  between  altered  and  unaltered  vein-matter,  476 ; 
on  the  geology  of  the  Cripple  Creek  district,  290;  on  the  geology  of  Cripple 
Creek,  Colo.,  343;  on  the  superficial  alteration  of  ore-deposits,  389  [433]. 

Pegmatites,  692. 

Pegmatite-veins  in  Norway,  647. 

Phillips,  J.  A. :  on  appearance  of  gold  at  Besseges,  France,  163 ;  classification  of  ore- 
deposits  by,  7. 

Phosphorus,  proportions  of,  in  the  earth's  crust,  639. 

Physico-chemical  principles  controlling  the  work  of  underground  waters,  317. 

Placer-deposits,  158. 

Platinum,  placer-deposits  of,  158. 

Platinum-metals,  original  proportions  of,  in  rocks,  640;  at  Sudbury,  Canada,  640;  at 
Klefva,  Sweden,  640. 

Pneumatolytic  minerals  in  veins,  694. 

Poiseuille's  law  of  the  flowage  of  water  in  capillary  openings,  297. 

Pontgibaud,  silver-lead  district,  France,  formation  of  lodes,  222. 

P5sEPNY\  PROF.  FRANZ;   The  Genesis  of  Ore-Deposits,  1 ;  remarks  in  discussion,  232. 

Posepuy  on  pipe-ore  of  Raibl,  Bohemia,  487 ;  on  stalactite  deposits  of  sulphide,  486. 

Potassium,  proportions  of,  in  the  earth's  crust,  639. 

Precipitation  in  the  zone  of  weathering,  479. 

Preferential  use  by  water  of  large  channels,  315. 

Prettau  in  Tyrol,  copper-mines  of,  143. 

Problems  in  the  Geology  of  Ore- Deposits  (VOGT),  636. 

Propylitic  andesite,  analysis  of,  566. 

Propylitization  of  rocks  (with  chloritization,  etc.),  660  efaeq.,  668. 

Przibram,  Bohemia :  ore-deposits,  56,  61,  76,  83,  239  et  seq. ;  Mining  Academy,  study  of 
geology  at,  9. 

Pseudomorphs,  phenomena  in  formation  of,  15. 

Psilomelane  in  ore-deposits  at  Romeneche,  France,  674. 

Pumpelly,  R. :  classification  of  ore-deposits  by,  7  ;  on  Lake  Superior  copper-deposits, 
144  •  on  the  metasomatic  development  of  copper-bearing  rocks  of  Lake  Superior, 
606;  on  metasomatism  in  ore-deposits,  509. 

Purington,  C.  W.,  on  the  gold-quartz  veins  of  Telluride,  Colo.,  592;  on  the  mining 
industries  of  the  Telluride  quadrangle,  Colo.,  417. 


802  INDEX. 

Py rite-deposits:  in  Germany  [651] ;  in  Hungary  [651];  in  Italy  [651].  FOREIGN 
COUNTRIES:  Italy:  Monte  Catini/457;  Norway,  651,  652;  Vigsnas  [457]  [676]; 
Fahlun  [676];  Rqros  [676];  Sulitelma  [676];  Spain:  Hnelva  provinces,  456; 
Rio  Tin  to,  456  ;  Eio  Tinto,  Huelva  district,  676  ;  Tharsis,  456;  Spain  and  Portugal 
[651] :  Sweden  :  Fahlun  [457]. 

Quartz-alunite  rocks,  formation  of,  661. 
Quartz-diaspore  rocks,  formation  of,  661. 
Queensland,  gold  in  coal-measures  of,  161. 
Quicksilver  at  Sulphur  Bank,  Cal.,  32  et  seq. 

Raibl,  Carinthia,  ore-deposits,  61,  69,  102,  134. 

Rain-water,  salt  in,  43. 

Rathgeb  gold-mine,  Calaveras  county,  Cal.,  750. 

RAYMOND,  R.  W. :  remarks  on  the  genesis  of  ore-deposits,  226,  252. 

Raymond's  classification  of  ore-deposits,  7,  226. 

Red  Mountain  district,  Colo.,  character  of  ore-deposits,  109. 

Reichensteiu  silver-mine,  Valle  Sacca,  Hungary,  description  of  ore-deposit,  101. 

Reyer,  Dr.  E.,  on  tin  placer-deposits,  159. 

Rezbaiiya,  Hungary,  geology  of  ore-deposits  at,  98. 

Rhodonite:  in  Veins  at  Broken  Hill,  Australia,  531;  at  Butte,  Mont.,  531;  at  Kap- 

nik,  Hungary,  531 ;  at  Real  del  Monte,  Mexico,  531. 
RICKARD,  T.  A. :  The  Formation  of  Bonanzas  in  the  Upper  Portions  of  Gold  Veins,  734  ; 

remarks  on  Posepny,  190,  211. 

Rickard,  T.  A.,  on  the  Enterprise  mine  of  Rico,  Colo.,  290,  342. 
Rio  Tinto,  Spain,  copper-mines,  621 ;  limonite  deposits,  148. 
Rock-cavities,  mineral  deposits  in,  15. 

Rock -salt  deposits  :  at  Maros  Ujvar,  Transylvania,  20;  of  the  Persian  Gulf,  21. 
Rodna,  Transylvania,  ore-deposits,  95. 

Role  of  the  Igneous  Bocks  in  the  Formation  of  Veins  (KEMP),  680. 
Rosario silver-mine.  Sun  Juancito,  Honduras,  Central  America,  493. 
Rosenbusch  on  the  genesis  of  pegmatite-veins,  732. 
Rubidium,  proportions  of,  in  the  earth's  crust,  639. 
Ruby  silver-mine,  Butte  district,  Mont.  [482]. 
Russia:  gold  placer-deposits  of  Ural  Mountains,  156;  ore-deposits  of  Kackar  district, 

in  the  Ural  [153],  157. 
Rutile  in  apatite-veins,  646. 

Salt,  in  rain-water,  43. 

Salt-mining  in  Austrian  Tyrol,  267. 

Sandberger,  Prof. :  on  fissure- veins  of  Schappach,  Schwarzwald,  594 ;  lateral -secretion 
theory  of,  57  et  seq.,  190,  200,  236, 242,  254,  257,  271 ;  occurrence  of  native  silver 
in  altered  granite  [506] ;  Przibram  rock,  analysis  of  samples  by,  62 ;  on  silver- 
veins  of  Wittich -Schwarzwald,  594. 

Sandstones:  copper,  of  Bohemia,  126;  at  Fontainebleau,  France,  119. 

Savage  silver-mine,  Comstock  Lode,  Nev.,  flood  of  water  in,  31. 

Santa  Rita  copper-mine,  Grant  county,  N.  M.,  449. 

Sawyer,  A.  R.,  on  Witwatersrand  gold-field,  South  Africa,  162. 

Saxony  :  tin-deposits  of  Altenberg  and  Zinnwald,  analysis  of,  542. 

Scandinavia,  ore- deposits  of,  140. 

Scapolitization  of  rocks,  660  et  seq.,  668. 

Schists:  copper,  124  et  seq.  ;  ore-deposits  in  crystalline,  137. 

Schiirmann,  E.,  investigations  in  sulphide  reactions,  468. 

Sea-mills  of  Cephalouia,  water-pow.r  of,  304. 

Sea-water:  metallic  sulphides  from,  188  ;  traces  of  metals  in,  121. 


INDEX.  808 

Second  concentration  favored  by  large  openings  of  the  belt  of  weathering,  378. 
Secondary  Enrichment  of  Ore-Deposits  (EMMONS),  433. 

Secondary  enrichment,  absence  of,  in  silver-lead  bodies  of  Cceur  d'Alene  district, 
Idaho,  488;  changes  of  water-level,  497 ;  chemical  processes  involved  in,  465  et 
seq, ;  effect  of  physiographic  and  climatic  changes,  496;  instances  of:  Australia: 
New  South  Wales;  Broken  Hill  lode,  459;  conditions  at  Butte,  Mont.,  440; 
Eastern  U.  S.,  452;  Mexico:  Chihuahua,  458;  Peru:  Cerro  de  Pasco  mining  dis- 
tricts, 458;  Spain  :  Huelva  provinces,  456;  Eio  Tinto,  456  ;  Tharsis,  456:  Western 
copper-deposits,  445;  Western  silver-deposits,  450;  zone  of  enrichment,  475  et 
seq.,  480;  solution  and  precipitation  of  gold,  481  et  seq,  ;  occurrence  of  bonanzas 
and  pay-streaks,  488  et  seq.;  of  veins  at  Neihart,  Mont.,  493  et  seq.;  zone  of 
weathering,  475  et  seq. ;  leaching  in,  476  et  seq.  ;  precipitation  in,  479. 
Sericitizatioii  of  rocks,  660  et  seq.,  668. 

Seven-Thirty  silver-mine,  Clear  Creek  county,  Colo.,  ore-veins  of,  216,  217. 
Shouldn't  Wonder  gold-mine,  Bright  district,  Australia,  746. 
Siberia,  Altai  region,  ore-deposits  of,  155. 
Siderite  in  lead-silver  veins  of  Co3ur  d'Alene,  Idaho,  527 ;  of  Wood  River,  Idaho, 

527. 

Silicates,  solutions  of,  319. 
Silicification  of  rocks,  661  et  seq.,  668. 
Silicified  diorite,  analysis  of,  593. 
Silicon,  proportions  of,  in  the  earth's  crust,  639. 

Silver-lead-miues :  Colorado:  Custer  county:  Geyser  (Security-),  351;  Montana: 
Boulder  county;  Eva  May,  495,  analysis  of  ore,  495;  Helena;  Frohuer,  496, 
Neihart;  Big  Seven,  484;  Florence,  484. 

Silver-mines;    Colorado:  Custer  County;  Geyser,  461 ;  Ouray  county;   Yankee  Girl, 
748;  Pitkin  county;  Mollie  Gibson,  450;  Smuggler,  450;  San  Juan  county  ;  Pan- 
dora, 451;  Smuggler-Union,  451 ;  Yankee  Girl,  451 ;  FOREIGN  COUNTRIES:  Aus- 
tralia :  New  South  Wales  ;  Broken  Hill  Consols,  460,  461;   Central  America  :  Hon- 
duras; Rosario,  493;  New  South   Wales:  Australian    Broken   Hill  Consols,  490; 
Norway:  Kongsberg,  468 ;  Montana:  Butte  district ;  Ruby  [482]. 
Silver  Plume  district,  Clear  Creek  county,  Colo.,  622. 
Silver  Reef  mining  district,  Utah,  130. 

Silver-  and  silver-lead  ores  :  in  Colorado,  202,  216  ;  Hartz  mountains,  80;  atLaurium, 
Greece,  135;  Nevada,  112,  198,  251;  Pontgibaud,  France,  222;  at  Raibl,  Carin- 
thia,  102;  at  Rezbauya,  Hungary,  98. 

Sjogren,  A. ;   on  iron-ore  deposits  in  Sweden,  138  ;   mines  of  Banat,  718. 
Slichter,  C.  S. :    on  the  motion  of  underground  waters,  309:  on  openings  in  rocks, 

294.' 

Slickensides:  formation  of,  213  et  seq. ;  at  Raibl  silver- lead  mines,  103 ;  in  Scandina- 
vian mines,  140. 
Smith,  George,  on  secondary  sulphides  at  Broken  Hill  Consols  mine,  N.  So.  Wales, 

Australia,  460,  461. 

Smuggler  gold-mine,  Cripple  Creek  district,  Colo., 290. 
Smuggler  lead -zinc  mine,  Aspen  district,  Colo.,  492. 
Smuggler  silver-mines,  Pitkin  county,  Colo.,  450. 
Smuggler-Union  silver-mine,  San  Juan  county,  Colo.,  451.  622. 
Soda-niter :  origin  of,  715. 

Sodium,  proportions  of,  in  the  earth's  crust,  639. 
Solutions  of  silicates,  319. 

Some  Principles  Controlling  the  Deposition  of  Ores  (VAN  HlSE),  282 ;  discussion  through- 
out later  pages  of  this  volume. 
Source  of  underground  water,  302. 
South  Africa,  gold-deposits  of,  162. 

South  Dakota  :  tin -ore  deposits :  Black  Hills,  643  (footnote). 
Snaces  of  discission,  14  ;  ore-deposits  in,  74. 

51 


804  INDEX. 

Spaces  of  dissolution,  14. 

Spain,  iron-ore  deposits  of,  148.     f 

Spurr,  J.  E. :  on  the  Aspen  mining  district,  Colo.,  342,  598;  on  the  geology  of  the 
Mercur  mining  district,  Utah,  407;  on  ore-bodies  of  the  Aspen  district,  Colo., 
492 ;  Pegmatite- veins  in  Yukon  section,  733. 

St.  Avoid,  copper-ores  in  sandstone  of,  127. 

Steamboat  Springs,  Washoe  county,  Nev.,  thermal  waters  of,  36  et  seq. 

Stelzner,  Prof.  A.  W. :  on  deposits  of  tin-ore,  159 ;  microscopic  methods  of  research 
[616];  on  pyritic  deposits,  652 ;  on  silver-tin  veins  in  Bolivia  [645]  (footnote); 
term  of  "  metasomasis "  proposed  by,  5;  on  tourmalinic  gold-copper  veins  in 
Chile,  546. 

Stokes,  H.  N.,  on  chemical  reactions,  471. 

Stream  detritus,  154. 

Striae  and  slickensides  as  proofs  of  movement,  213  et  seq. 

Strontium,  proportions  of,  in  the  earth's  crust,  639. 

Structural  features  of  the  deposits  of  mineral  springs,  52 

Struggl  silver-lead  mine,  Eaibl,  Carinthia,  ore-bodies  of,  104. 

Subterranean  water-circulation,  18,  219,  253. 

Subterranean  waters,  heat  of  ascending,  31. 

Sugar  Loaf  gold-mine,  Kunanalling,  W.  Australia,  742. 

Sulphide  enrichment  in  veins  of  Freiberg,  Saxony,  615. 

Sulphide  ores,  effect  of  ferric  salts  upon,  676  (footnote). 

Sulphur  Bank  quicksilver-mine,  Lake  county,  Cal.,  thermal  waters  at,  32  et  seq,,  256. 

Sulphur,  proportions  of,  in  the  earth's  crust,  639. 

Surface-flows  of  igneous  rock  unfavorable  to  vein-formation,  694. 

Sweden:  Amuieberg,  zinc-blende  mine  at,  141;  copper-  and  gold -ores,  140;  pla- 
tinum-metals at  Klefva,  640 ;  Taberg,  iron-ore  deposits  of,  138. 

Switzerland,  Carniola,  iron-ore  deposits  of,  136. 

Taberg,  Sweden,  iron-ore  deposits,  138. 

Talhawang  gold-district,  New  South  Wales,  161. 

Tasmania,  gold  in  coal-measures  of,  161. 

Tellurium :  in  quartz-veins  at  Cripple  Creek,  Colo.  [654] ;  at  Hauraki,  New  Zealand 

[654] ;  at  Nagyag,  Hungary  [654]. 
Temperatures,  critical,  of  water,  etc.,  659, 
Temperature :  of  magmas,  659  ;  of  mineral  waters,  40. 
Thames  gold-field,  New  Zealand,  221. 
Thermal  waters  encountered  in  mines,  29,  30. 
Thermo-dynamic  relations  between  hot  water  and  soft  glass,  308. 
Thuringia,  Tcupferschiefer  of,  124. 
Tin,  proportions  of,  in  the  earth's  crust,  639. 
Tin-deposits :  of  Altenberg  and  Zinnwald,  Saxony,  analysis  of,  542 ;  of  Etta  Knob, 

S.  Dak.,  643  (footnote) :  of  Cornwall,  England,  139;  placer-deposits,  158. 
Tin-,  copper-  and  galena- veins  in  Cornwall,  Eng.  [657]. 
Titanomagnetite-olivinite  deposit  at  Taberg,  Sweden,  138. 
Titanic  acid  in  apatite-veins,  646. 
Titanium,  proportions  of,  in  the  earth's  crust,  639. 
Tornebohm,  A.  E.,  on  contact-deposits  at  Pifckiiranta,  Finland  [650]. 
Trade  Dollar  copper-silver  mine,  Florida  Mountain,  Idaho,  573. 
Transylvania:  Daciaii  gold-district,  86;  mining  rock-salt  at  Maros  Ujvar,  20;  Veres- 

patak  gold  deposits,  66  et  seq.,  87  ;  Vulkoj  gold  deposits,  88. 
Transvaal,  South  Africa,  Witwatersrand  gold-fields,  162. 
Tresavean  copper-mine,  Cornwall,  621. 
Tyrol:    copper-mines  of  Prettau,  143;    iron-ore  deposits,   143;   salt-mining  at  the 

Salzkammergut,  267. 


INDEX.  805 

Underground  waters  :  see  innumerable  passages  throughout  this  volume. 

United  Verde  copper-mines,  Yavapai  county,  Ariz.,  447. 

Union  Copper  Co.'s  copper-mine,  Gold  Hill,  Rowan  county,  N.  C.,  454. 

Ural  mountains,  gold-districts  of,  76. 

Utah  :  character  of  ore-deposits,  110;  Silver  Reef  mining  district,  130. 

Vadose  underground  circulation,  18;  filling  of  open  spaces  formed  by,  23;  probable 

source  of  some  deep  ore-deposits,  197,  198. 
Vadose  vs.  deep  circulation,  276. 

Valle  lead-mines,  Jefferson  county,  Mo.,  character  of  deposits,  71, 115. 
Vanadium,  proportions  of,  in  the  earth's  crust,  639. 
VAN  HISE  (C.  R.) :  Some  Principles  Controlling  the  Deposition  of  Ores,  282;  remarks  in 

discussion,  731. 

Vapors  or  dissociated  gases  in  igneous  rocks,  686, 
Vein-formations,  sequence  of,  690. 
Vein-minerals :  association  of,  658 ;  deposition  of,  659. 
Veins,  role  of  the  igneous  rocks  in  the  formation  of,  680  et  seq. 
Verchoviky,  or  surface  ore-deposits,  152. 

Verespatak,  Transylvania,  structure  of  gold-deposits  at,  66,  87. 
Vermont,  copper-deposits  of,  207. 

Vesuvius  lea^-mine,  Bavaria,  Germany,  tree-stems  changed  to  galena  at,  129. 
Victor  gold-mine,  Cripple  Creek  district,  Colo.,  290. 
Vogelgesaug  on  dissemination  of  native  silver  in  gneiss  [506]. 
VOGT,  PROF.  J.  H.  L. :  Problems  in  the  Geology  of  Ore-Deposits,  636. 
Vogt's  account  of  cassiterite-veins  in  Telemarken,  Norway,  563  ;  of  concentration  of 

gold  and  silver  beneath  "  iron  hat"  in  Rio  Tinto  region,  Spain,  487. 
Von  Fircks,  W.,  on  the  tin-deposits  of  Mt.  Bischoff,  Tasmania,  543. 
Von  Inkey,  Bela,  on  the  ore-deposits  of  Nagyag,  Hungary,  568. 
Vulkoj  gold-mines,  Transylvania,  character  of  ore-deposits  of,  86. 

Waldstein,  classification  of  ore-deposits  by,  4. 

Waters:  analysis  of,  from  mineral  springs,  37,  42  ;  ascending,  encountered  in  mines, 

28;  subterranean  circulation  of,  18,  219,  253  et  seq. 

WEED,  WALTER  HARVEY  :  The  Enrichment  of  Gold-  and  Silver-  Veins,  473. 
Weed's  account  of  the  copper-deposits  of  the  Southern  Appalachian  region,  453;  of 

the  Elkhorn  mine,  Mont.,  597 ;  of  the  mines  of  Neihart,  Mont.,  452. 
Weidman,  S.,  on  igneous  rocks  of  Fox  River  Valley,  Wis.  [289]. 
Well-waters  of  Tucson,  Ariz.,  analysis  of,  714. 
Werner,  A.,  theory  of  ore-deposits  of,  3. 

Westphalia:  copper-ores  of,  125;  pisolitic  formation  at  Warstein,  67. 
Whitney,  Prof.  J.  D. :  classification  of  mineral  deposits  by,  6  ;  on  lead-  and  zinc-ores 

of  Wisconsin,  118. 

WINCHELL,  HORACE  V. :  in  discussion  of  the  genesis  of  ore-deposits,  192,  227. 
Winklehner,  H.,  on  rock-salt  deposits  of  the  Persian  Gulf,  21. 
WINSLOW,  ARTHUR:  in  discussion  of  the  genesis  of  ore-deposits,  188. 
Wisconsin,  lead-  and  zinc-regions  of,  115, 117,  189  et  seq. 
Witwatersrand  gold-field,  Transvaal,  South  Africa,  162. 
Woodward,  John,  "  Essay  Towards  a  Natural  History  of  the  Earth,"  192. 

Xeuogenites  in  general,  12. 
Xenogenous  mineral  deposits,  10. 

Yankee  Girl  silver-mine,  Ouray  county,  Colo.,  748. 

Yankee  Girl  silver-mine.  San  Juan  county,  Colo.,  451. 

Yellow  Jacket  silver-mine,  Storey  county,  Nev.,  location  of  ore,  93. 


806  INDEX. 

Yellowstone  National  Park;  analysis  of  water,  42;  chimney-like  conduits  built  by 

geysers,  39. 

Yttrium,  proportions  of,  in  eartb's  crust,  639. 
Yukon  section  ;  Pegmatite  veins  in,  733. 

Zeolitization  of  rocks,  661  et  seq.,  669. 

Zinc-blende,  proportion  of,  increasing  with  depth  of  deposit,  673. 

Zinc-ores:  Ammeberg,  Sweden,  141 ;  Wisconsin,  117,  189  et  seq. 

Zirconium,  proportions  of,  in  the  earth's  crust,  639. 

Zones  of  weathering,  of  enrichment,  and  of  primary  sulphides,  475  et  seq. 

Zone  of  combined  fracture  and  flowage,  288. 

Zoppe,  G.,  on  salt  in  rain-water,  43. 


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